Weigh feeder system

Abstract

Disclosed herein is an automatically controlled weigh feeding apparatus including a container prefilled with a substance, a device for discharging the substance from the container at a controllable rate, apparatus for weighing the container and its contents and for producing an electrical signal proportional to that weight, a first amplifier for amplifying the electrical signal, a first analog-digital converter coupled to said first amplifier and a digital computer coupled to said first analog-digital converter for computing the weight of substance remaining in the container. A second amplifier is coupled to said first amplifier and a ramp off-set circuit which is controlled by the digital computer inputs a second signal to the second amplifier means having a controlled stepping output applied as a second input signal to the second amplifier to maintain the output of the second amplifier within a given selected range of amplitude during one time cycle of operation. A second analog-digital converter interposed between the second amplifier and the digital computer. The digital computer is adapted to compute a corrective signal based on the signal received for controlling the discharge of the substance from the container.

Description

This invention relates to weigh feeding systems and it is particularly applicable to apparatus for feeding fluid-like material. Systems constructed according to the present invention are particularly adapted, among other possible uses, for accurately weigh feeding a wide variety of substances including dry materials regardless of whether the material is free-flowing, sluggish, or pressure sensitive; and ranging from amorphous powders to flakes, pellets, chunks and even fibers, as well as liquids.

Various control weigh feeding systems have been known in the past, as for example, the system disclosed in U.S. Patent Application Ser. No. 345,587, filed Mar. 28, 1973. In accordance with this application, there is provided a weigh feeding apparatus wherein the discharge rate of a fluid substance from a container is maintained at a predetermined constant value. The container and its contents are weighed, and an electrical signal is produced which signal has an amplitude proportional to the weight of the container and its contents. This electrical signal, which varies as the contents of the container are discharged, is differentiated and applied to a comparator circuit together with a reference signal, wherefore the output of the comparator circuit may be used to control said discharge rate of the substance as it is fed from the container. The comparator output is applied to a signal generator for producing a motor drive signal for a DC motor having its output shaft connected to drive a device for discharging the substance from the container. The signal generator may comprise a pulsing circuit for controlling a pair of SCR's which are disposed in a rectifying bridge circuit connected between an AC voltage source and the input of the DC motor. Accordingly, the speed of the motor is controlled by the pulsing circuit, which, in turn, is controlled by the algebraic sum of the output signal of a tachometer generator which is coupled directly to the motor shaft, and output signal from the comparator. It can be stated that the above-described apparatus provides an accurate weigh feeding system, whereby the feeding rate may be maintained at a constant value, and wherein the predetermined feeding rate may be adjusted by adjusting the value of the reference signal source.

Additionally, the output of the weighing device may be applied to a pair of differential amplifier circuits, along with a pair of reference voltage inputs, for determining when the contents of the container varies above and below desired maximum and minimum fill levels for the container. That is, circuitry is provided for automatically refilling the container when the weight of the substance therein reaches the desired minimum weight, and for terminating the filling process for the container when the fluid substance therein reaches the desired maximum weight. Such circuitry includes means for maintaining the discharge rate of the container at a constant rate equal to the instantaneous rate thereof immediately preceding energization of the filling device for the container. Particularly, the pair of differential amplifier circuits are coupled to a pair of relay driver circuits for controlling a relay circuit to energize the filling device when the substance in the container reaches the minimum weight, and for maintaining that filling device in an energized state until the container is refilled to its maximum desired level. The relay circuit is also coupled to the comparator circuit, for controlling the latter to produce a constant output during the refilling process for the container, thereby maintaining the discharge rate of the container at the value of the particular discharge rate thereof immediately preceding energization of the filling device.

As pointed out in said patent application, Ser. No. 345,587, in certain installations there exists a possibility of physical forces impinging upon the weigh feeder from an external source, such as wind or air currents, physical contact with the weigh feeder by operating personnel, or the like, for example. These forces cause the weigh feeder to move at a rate that is other than that resulting from the linear discharge of the contents of the container. Because such additional movement, i.e. acceleration, is an error and has no direct relationship to the actual discharge of material from the container, the control system could continue to perform its corrective function utilizing the erroneous output signal for comparison with the fixed set point reference signal derivative. The aforementioned patent application discloses one means for preventing such excessive and abnormal movements of the weigh feeder scale from grossly affecting or disturbing the normal operation of the system to thereby prevent large excursions of the output feed rate.

The present invention is directed to new improved means for accomplishing the foregoing objectives, as well as additional objectives, as will become apparent as the description proceeds.

Another feature of the present invention resides in the provision of a new and improved weigh feeder system, which is capable of controlling more operating parameters, which operates faster, which provides a faster responsive action, and which is more accurate as compared to the prior art systems. In addition, the feeder system of the present invention has a memory and is capable of taking into account past errors in the material flow rate and taking corrective action with respect thereto.

Also, the system is capable of disregarding single extraneous material flow rate readings, which may be caused by such factors as noise, vibrations, or the like, for example.

In one form of the invention, we provide a new and improved weigh feeding apparatus characterized by a container for a prefilled substance having means for discharging the substance therefrom at a controllable rate. A scale system is provided for weighing the container prefilled with the substance and an electrical circuit serves to produce a first electrical signal proportional in amplitude to the weight, and a high gain amplifier amplifies the electrical signal. An analog-digital converter (ADC) is coupled to the amplifier and a digital computer is adapted to receive pulse signals from the ADC for computing and outputting a signal corresponding to the signal received. Digital-analog converter ramp offset means which is controlled by the computer outputs a controlled stepping signal, that is applied as a second input to the amplifier means to algebraically combine therewith. Each step corresponds to one time cycle of operation, thereby maintaining the output of the amplifier in a given preselected range of amplitude during one time cycle of operation. The digital computer as another operation thereof computes a corrective signal based on the signal received, and means coupled between the computer and the means for discharging the substance from the container, serve to control the rate of discharge responsive to the corrective signal.

According to one aspect of the invention, the weigh feeder apparatus further comprises means for inputting into the digital computer a preselected feed rate, and the computer is adapted to store in memory a series of signals received from the ADC for each of the time cycles of operation and compute a corrective signal by comparing the signals received with the preselected feed rate. According to another aspect of the invention, the weight feeding apparatus further comprises an under-weight limit input means to the computer and an overweight limit input means thereto. The computer, as one operation thereof, causes an underweight or an overweight light to energize when an underweight or an overweight condition exists for longer than some preset period of time. Further, according to another aspect of the invention, the digital computer computes the corrective signal, while disregarding a preselected number of the signals received from the ADC, which exceed a set limit during one time cycle of operation, when computing the corrective signal.

The invention provides, according to another form thereof, a new and improved weigh feeding apparatus which is characterized by a container for a prefilled substance and means for discharging the substance from the container at a controllable rate of weight loss. A scale is provided for weighing the container prefilled with the substance and an electrical circuit is coupled to the weighing means for producing a first electrical signal proportional in amplitude to the weight determined by the weighing means. A first amplifier amplifies the electrical signal and a first analog-digital converter (ADC) is coupled to the first amplifier and outputs binary words to a digital computer coupled thereto. The digital computer, as one operation thereof, computes a first output signal corresponding to the weight of the substance in the container. A second amplifier amplifies a signal received from the first amplifier and a second ADC is coupled to the second amplifier and outputs a binary word signal to the digital computer. Digital-analog converter ramp offset means are provided which receive a signal from the digital computer and outputs a controlled stepping output which is algebraically combined with the input to the second amplifier, each step corresponding to one time cycle of operation, thereby to maintain the output of the second amplifier in a given preselected range of amplitude during one time cycle of operation. An input switch is provided to apply a preselected feed rate value to the computer. The computer, as another operation thereof, stores in memory a series of said signals received from the second ADC for each of the time cycles of operation and computes a corrective signal by comparing the signals received with the preselected feed rate value. Coupling means interconnect the computer and the means for discharging the substance from the container, whereby the corrective signal serves to control the rate of discharge of the substance from the container. A shaft encoder is coupled to the computer to allow vibration signals generated from the rotating machinery mounted on the scale to be corrected for in the computation of the feed rates.

In still another form of the invention there is provided a weigh feeding apparatus which includs a container for a prefilled substance, means for discharging the substance from the container at a controllable rate, means for weighing the container prefilled with the substance, and means coupled to the weighing means for producing electrical signals proportional to the weight determined by the weighing means. In addition, the apparatus further includes an analog-digital converter for receiving the electrical signals, digital computer means coupled to the analog-digital converter for computing a corrective signal based on the signals received, and means coupled between the computer means and the means for discharging the substance from the container for controlling the rate of discharge responsive to the corrective signal. Further, this weigh feeding apparatus comprises, means for inputting into the computer means a preselected feed rate, said computer means being adapted to store a series of the signals received from the analog-digital converter for a time cycle of operation and computing said corrective signal by comparing the signals received with the preselected feed rate, and said computer being further adapted to maintain the corrective signal constant during the time when a preselected number of the signals received from the analog-digital converter exceeds preselected upper or lower limits, during one time cycle of operation.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described more fully hereinafter. Those skilled in the art will appreciate that the conception on which this disclosure is based may readily be utilized as the basis of the designing of other structures for carrying out the various purposes of the invention. It is important, therefore, that this disclosure be regarded as including such equivalent constructions and methods as do not depart from the spirit and scope of the invention.

One embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings forming a part of the specification, wherein:

FIG. 1 is a block diagram of the weigh feeder system constructed in accordance with the concepts of the present invention;

FIG. 2 is a graphic representation of the output voltage with respect to time of one of the amplifier circuits of the present invention;

FIG. 3 is a graphic representation of the output of a controlled ramp offset circuit of the present invention;

FIG. 4 is a graphic representation of the output of a second amplifier circuit;

FIG. 5 is a graphical representation of the actual measured feed curve as compared to the desired feed curve;

FIG. 6 is a graphic representation of the positional relationship of the shaft encoder with respect to the material being fed;

FIG. 7 is a graphic representation of the output of the second analog-digital converter with respect to time, before correction for induced system noises;

FIG. 8 is a graphic representation of the output of the second analog-digital converter with respect to time, after correction for induced system noises;

FIG. 9 is a flow chart of the wait subroutine;

FIG. 10 is a flow chart of the one second interrupt display subroutine;

FIG. 11 is a flow chart of the derive subroutine;

FIGS. 12A, 12B and 12C is a flow chart of the main routine of the computer;

FIG. 13 is a flow chart of the calculate subroutine; and

FIG. 14 is a flow chart of the learn mode subroutine.

The weigh feeder system of this invention, as shown diagramatically in FIG. 1, includes a feeder assembly indicated generally at 10, which comprises a container 12 with a discharge device connected thereto for feeding the substance 14 out of the container and through a discharge conduit 16. As illustrated, a DC motor 18, connected to a gear-reduction device 20 is provided for driving the discharge device. The feeder assembly may comprise an auger mechanism as disclosed in detail in U.S. Pat. No. 3,186,602 issued June 1, 1965. The entire feeding assembly, including the container, the discharge device, the motor, and the gear-reduction device is mounted on a scale 22, which may comprise a structure as described in detail in U.S. Pat. No. 3,494,507, issued Feb. 10, 1970.

In accordance with the invention there is provided a detecting device, as for example, a linear variable differential transformer (LVDT) 24, coupled to the scale for providing an electrical signal having an amplitude which is proportional to the weight of the container and its contents. That is, as the contents of the container 12 are discharged, a relative movement occurs between the windings and the core of the LVDT, thereby causing a varying output voltage proportional to the varying weight of the container and its contents. Thus, as the substance is discharged from the container, the LVDT provides an electrical signal which varies in response to such discharge, which may, for example, be a DC voltage with a range of the order of from .DELTA.3 volts to .DELTA.6 volts when the material in the container drops from its upper level to its lower level. The signal from the LVDT is applied to a summing junction 26 by a conductor 28, through a resistor 30. Also, applied to the summing junction 26 is an offset potentiometer means 32, by a conductor 33 through a resistor 34, to render the signal from the LVDT symmetrical with respect to zero as measured at 38. The output from the summing junction 26 is applied to an amplifier 35, having a gain potentiometer 36, to produce an output signal at 38, which ranges, for example, from -10 volts when the container 12 is full to a +10 volts when the container is empty, as shown by the curve in FIG. 2. The output signal from the amplifier 35 is applied to a conventional analog-digital converter (ADC) 40, by way of a conductor 42, wherein the offset amplified LVDT signal is measured and digitalized and outputted as digital words, corresponding to the total scale weight, i.e. the quantity of material contained in the container 12. Any suitable type of ADC may be employed such as a 12 bit, Model No. 124-10 XW 3, as manufactured by Analog Devices, Inc.

In addition, the output signal from the amplifier 35 is applied through a resistor 43 to a second amplifier 44, having a feed back resistor 46, thereby to provide a gain of the order of about a 700 multiple. Applicants have found that a gain of this order is necessary in order to make the desired calculations later in the system, but with such a gain, the voltage would normally be too high, as a practical matter, for computational use, and therefore, a controlled ramp offset signal is also applied to a summing junction 47 by a conductor 48 through a resistor 49. This offset signal is provided by a ramp offset digital-analog converter (DAC) 50, which receives controlled digital words or binary bits and converts them to a step-shaped signal, having a frequency corresponding to one time cycle of operation of the process system, as shown by the curve in FIG. 3. This ramp offset functions in cooperation with the amplifier 44 so that a controlled quantity is subtracted from the input to the amplifier, whereby during one time cycle of operation the output from the amplifier 44 gradually decreases from about +5 volts to about -5 volts. The ramp offset 50 is a fast acting electronic servo (typically 50 microseconds), and is controlled so that between time cycles of operation its output is adjusted one step as shown in FIG. 3. Thus, at the beginning of the next succeeding time cycle, the output from the amplifier 44 is again about +5 volts as shown in FIG. 4. Any suitable type of ramp offset DAC may be employed, such as a 14 bit Model ZD354M1, having a resolution of 1 part in 10,000, as manufactured by Zeltex, Inc., for example. The amplifiers 35 and 44 may be of any suitable type such as Model OPO5EJ, as manufactured by Precision Monolithics, Inc., for example.

The output from the amplifier 44 is applied to a conventional 12 bit analog-digital converter (ADC) 52 by a conductor 54, wherein the output signal from the amplifier is measured and digitalized. The output from the ADC is in the form of digital words corresponding to the scale weight, but greatly amplified.

A binary number system is employed as the code for information handling because of certain advantages hereinafter brought out. Thus, as seen in FIG. 1, the weigh feeder system is provided with a digital computer 56, which includes processing, memory and control systems. Any suitable digital computer may be employed such as a micro processor Model IMP16C/300 and memory Model IMP16P/004P, as manufactured by National Semiconductor Corp., for example.

Still referring to FIG. 1, a plurality of inputs are applied to the processor to control the same. A conventional off-on switch 58 serves to control the main power supply to the processor. A switch 60 is provided whereby the refill sequence may be automatically actuated (switch in "auto") when product level reaches low level, or at any product level (switch in "manual") or, the refill sequence may be bypassed (when switch is in "bypass"). The refill sequence is a procedure wherein the motor speed will not lockout for refill thereby actuating the refill controller until the computer first senses that the scale is undisturbed by foreign influences and secondly, senses that the feed rate agrees with the set point. Input switch 62 serves to convert the system between gravimetric control and volumetric control, as desired. This will be explained more fully hereinafter. A reset total push button switch 64 serves to reset the processor for an entirely new batch of data. Also, there is provided a scale weight switch 66, that inputs into the processor the scale weight, S, which is determined by the size or model of the feeder assembly 10 being employed in the particular installation. This factor is set once and is not adjusted unless a new model or size of feeder assembly is installed.

A motor speed input switch 67 is provided, which is set by the operators at a preselected percent in the range between 0% and 100%, to input into the processor the desired operating speed of the motor when operating volumetrically.

Input switch 68 is actuated by the operator to input the desired feed rate R (LBS./HR) into the processor. This is a 16 bit digital word, stored in memory, that represents the desired slope of the feed line or curve 70, FIG. 5. Input switch 72 is also actuated by the operator to input the underweight set point into the processor memory. It represents the selected minimum limit of the feed rate range, as is indicated by the dotted line 74 in FIG. 5. This limit is expressed as a percentage of from 0 to 9.99% below the desired feed rate R. Input switch 76 inputs the overweight set point into memory. It represents the selected maximum limit of the feed range, as is indicated by the dotted line 78 in FIG. 5. This limit also is expressed as a percentage of from 0 to 9.99% above the desired feed rate R.

Still referring to FIG. 1, digital switch 80 is an operator activated switch to input into the memory, the desired minimum or low level of the material in the container 12. The range of this switch is from 0 to 99.9%. Thus, for example, if the operator desires the system to shift into its refill mode when the container 12 is down to 5% of its capacity, he sets the low level switch 80 at 05.0%. Digital input switch 82 is an out of low level switch with a range of from 0 to 99.9% so that the operator can input into memory the desired level for the system to shift out of its refill mode to its normal operative mode. Thus, for example, the operator could set this switch for 90.0%, whereby when the container 12 reaches 90% of its capacity, the system would shift out of its refill mode to its normal operative mode.

In addition, the processor also receives a signal from a shaft encoder 83. This allows a correlation to be made between system noises induced by the movement of the machinery mounted on the scale or movement of the product in the storage hopper. This correlation may then be used as a correction factor, subtracting out noise components due to moving machinery on the scale such as for example, the motor, gear box, augers, as well as movement of the material in the container. The processor 56 is provided with a learn mode input switch 85, which is shiftable between normal operation and learn mode operation. When a new material is going to be processed by the system or when the system is first installed, the system is set in operation, but instead of discharging the substance 14 out of the system, it is collected in a small container, not shown, and retained on the scale 22 so that there is no net loss of weight from the scale. The switch 85 is shifted to its learn mode position. The motor 18 is run throughout its speed range and the shaft encoder 83 picks up the noise corresponding to the rotational position of the drive shaft and sends out digital signals to the processor, which are stored in memory. After this information has been stored in memory, the small container is removed from the scale and the switch 85 is shifted to its normal operation. FIG. 6 illustrates the positional relationship of the shaft encoder 83 with respect to the material being fed. FIG. 7 illustrates the output of the ADC 52 with respect to time, before it is corrected for the induced system noises. Processor 56, as another operation thereof, subtracts the stored data from the data received from the ADC 52 to present a relatively straight line of this information for processing. FIG. 8 illustrates the corrected output from the ADC 52 for one time cycle of operation. Any suitable type of shaft encoder may be employed such as a Series 2500, Optical Encoder, as manufactured by Renco Corporation.

The microprocessor 56 has, as an output, a display device 84 which indicates the total feed commanded. This device indicates the total feed asked for by the operators over a relatively long period of time. Thus, the processor, as one operation thereof, receives the selected feed rate R from the input switch 68 and integrates it with respect to the elapsed time and continuously displays the total feed commanded, in pounds. As another output there is provided a display device 86 which indicates the actual total feed discharge from the feeder assembly 10. Thus, the processor, as one operation thereof, receives a signal from the ADC 40 corresponding to the total scale weight, which indicates the guantity of material remaining in the container. This signal represents the amount of weight of material in the feeder 12. Any change in this signal, except during refill, represents the amount of material fed. These changes are totalled by the processor to give the actual total feed, in pounds. During refill the amount of material fed is computed by the processor from the reading of the feed rate meter and the time it takes to refill. When refill is completed the signal from the ADC 40 is again used to compute the total amount of material fed. The operators can compare the actual total feed, as displayed at 86, with the total feed commanded, as displayed at 84, to determine how the system is functioning and, if necessary, take corrective action.

A feed rate display device, such as a four digit meter, 88, for example, shows the actual feed rate in pounds per hour of the feeder assembly. Thus, the processor, as another operation thereof, receives the amplified scale weight signal from the ADC 52 and corrects this signal as pointed out hereinbefore, and then differentiates the signal with respect to time to produce a signal indicative of the present rate of feed. This can be visually compared to the desired feed rate as set by the input switch 68 to determine possible malfunctions in the system.

A scale weight display device, such as a three digit meter 90, for example, is provided to indicate the actual percentage of product remaining in the container 12 on the scale 22. Thus, the processor, as still another operation thereof, receives a signal from the ADC 40 corresponding to the weight on the scale 22 and computes the actual percentage of material remaining in the container 12. Next, there is provided, as another output of the processor 56, a three digit motor speed meter 92 which indicates the actual speed of the motor 18. That is, the processor receives a signal from a tachometer 93, indicating the speed of the motor 18, by a conductor 95 through a conventional analog-digital converter 97, and outputs a motor speed on meter 92. While this speed is usually relatively constant, it may vary to some extent over a long period of time. It is advantageous for the operator to know, as any sudden variations may indicate a blockage of material in the system.

In addition, there are provided operational and warning indicators, such as lights, buzzers, or the like, for example, for purposes of keeping the operators informed. An underweight light 94 indicates when the actual feed rate, as indicated by the meter 88, falls below the underweight set point 72, and an overweight light 96 indicates when the actual feed rate exceeds the overweight set point 76. That is, when the actual feed rate falls below the line 74, FIG. 5, which is set by the underweight set point switch 72, the underweight light 94 is actuated, and when the actual feed rate is above the line 78, FIG. 5, which is set by the overweight set point switch 76, the overweight light 96 is actuated. Preferably, there is a preselected time delay period of from about 0 to about 3 minutes delay after the feed rate meter 88 indicates an overweight or an underweight condition before the warning lights are actuated. Light 98 shows when the system is in its refill mode, i.e. when the container 12 is being refilled. The light 100 indicates that the system is in its ACRILOK mode. This mode of operation will be explained more fully hereinafter. Run light 102 indicates that the system is in operation and standby light 104 indicates that the system power has been applied, but all machinery is stopped. The light 106 indicates that the bin 12 is in its low level condition.

A control output 108 from the processor 56 is applied to a digital-analog converter (DAC) 110. Any suitable type of DAC may be employed, such as a 10 bit Model AD7520L, as manufactured by Analog Devices, Inc., for example. In the DAC, the digital pulses are converted to an analog signal, which is applied to the tachometer 93 and an SCR motor control 112. Any suitable type of motor control may be employed such as Acrison, Inc.'s Model ACR100BTG, for example. This controller produces an output which is applied to the motor 18 to control the speed thereof, and thereby control the discharge rate of the material from the feeder assembly 10.

In operation, the operator must determine whether he wishes to operate in the volumetric mode or the gravimetric mode. If the volumetric mode is selected, then the operator sets the motor speed switch 67 to the desired motor speed. In this mode of operation, the output of the processor is a digital word conveyed by conductor 108 to the DAC 110. The DAC causes a voltage from 0 to 6 volts to appear on conductor 111 and the SCR motor control adjusts the speed of the DC motor 18 unitl the output of the tachometer 93 exactly equals the voltage on the conductor 111. While this mode of operation is desirable at certain times, it does not provide as high a degree of accuracy as the gravimetric mode and, consequently, the gravimetric mode is predominantly employed.

In operation, when the operator sets the switch 62 to the gravimetric mode of operation, the operator then sets the feed rate switch 68 to the desired feed rate R (LBS./HR), which, as discussed hereinbefore, determines the slope of the feed curve or line 70, FIG. 5. The processor then computes the conversion time which may be, for example, T = S/R (2.5) in seconds, where S is the scale weight as set by switch 66. Next, the ramp offset 50 is energized which, as pointed out hereinbefore, limits the range of the output 54 of the amplifier 44 to between +5 volts and -5 volts. Initially, it sets said output at about +5 volts. Next, the processor starts the conversion time. The conversion time T, may, for example, be about 250 milliseconds. A plurality of samples are taken based on the input from the ADC 52, which may for example, be about 100. The conversion time, T, or time to complete one cycle of operation is selected to be within the range of from about one-fourth seconds minimum to a maximum of from about 100 to 200 seconds. During this cycle, the output from the amplifier 44 moves from about +5 volts to about -5 volts. Each sample is stored in memory. The samples, generally illustrated in FIG. 5 by dots, form the actual feed curve 114. One of the most important operations of the processor is to compute a regression analysis on these samples with respect to time T, and thence compute the RMS error on T.

FIG. 5 illustrates an upper 3 RMS error line at 121 and a lower 3 RMS error line at 123. If less than 20, for example, sample data points exceed 3RMS error in either direction, as indicated at 115 in FIG. 5, regression on T is recomputed with the data points exceeding 3 RMS, as indicated at 117, excluded. Thence, the computed slope of the actual feed curve is compared with the slope of the desired or set point feed line, and a corresponding correction command is outputted at 108 to adjust the motor control 112, thereby to adjust the actual rate of discharge of the material from the feeder assembly 10. This time cycle of operation is continuously repeated to continuously adjust the motor control 112.

If more than 20, for examle, sample data points exceed 3 RMS error in either direction, as indicated at 119 in FIG. 5, the system is changed into its ACRILOK mode. That is, the ACRILOK light 100 is energized and the output command 108 to the DAC 110 and motor control 112 is not updated, but continues in its present state. That is, the processor continues to receive sample signals from the ADC 52 and compute the regression analysis thereof, but no correction command is outputted at 108. The feed rate meter 88 is also locked at the last control data point. The feed system remains in a locked condition unitl in a subsequent time cycle of operation less than 20 data points exceed 3 RMS error, and then the system is returned to its normal operating mode and the correction command is again outputted at 108.

As still another operation of the processor, the total feed commanded, as indicated at 84, is compared to the actual total feed, as indicated at 86, periodically, such as every 5 or 10 minutes, for example. If there is a deviation exceeding predetermined limits, the processor modifies the aforementioned command output at 108 to gradually correct the actual feed to the total feed. This is programmed to take from about 5 minutes to about 10 minutes, thereby to avoid sharp fluctuations in the feed rate command, but nevertheless, obtain as close as possible the total feed selected over a long period of time.

A further operation of the processor, is to determine when the scale weight, as indicated by the meter 90, drops to a predetermined low level, as set by the low level switch 80, and then search for an "on rate" condition. That is, the output signal outputted at 88 is monitored until the difference between it and the feed rate switch 68 is less than a predetermined error limit. Thence, the system is changed into its refill mode wherein the output command 108 and feed rate meter 88 are not updated, but are retained in its present state, similar to its operation as described hereinbefore in connection with the ACRILOK mode. At the same time, a command is outputted to a refill circuit 120, which sends a signal to a refill controller 122 that controls the flow of material from a refill source 124 to the container 12. The controller 122 could be an AC motor when handling dry particulate material or could be a valve when handling liquids.

The system remains in the refill mode until the processor detects that the container 12 is refilled, as indicated by the scale weight meter 90, and as selected by the out of low level switch 82. At this time, the processor outputs a signal to the refill circuit 120 which, in turn, directs the refill controller 122 to discontinue refilling the container 12. The processor then returns the system to its normal operational mode.

FIGS. 9 to 14 are various flow charts of the computer 56. Thus, FIG. 9 is a flow chart showing the wait subroutine, and FIG. 10 is a flow chart of the second interrupt subroutine, which is a display type subroutine. FIG. 11 is a flow chart of the derive subroutine wherein the normal conversion time is calculated. FIGS. 12A, 12B and 12C combine to form a flow chart of the main routine of the computer 56. FIGS. 13 and 14 are flow charts of the calculate and learn mode subroutines, respectively.

______________________________________GRAV/VOL. = GRAV.ON/OFF = OFFAUTO/MAN./BY-PASS = AUTOSCALE WEIGHT = 1000. lbsFEED RATE SET POINT = 200 LBS./HRINTO LOW LEVEL = 20%OUT OF LOW LEVEL = 80%MOTOR SPEED = 50%ASSUME MAX. FEED RATE = 2000 LBS./HROF MACHINEREAL TIME CLOCK RATE = 1 KHZ (Clock causes interrupt)______________________________________

Flags set by hardware:

Grav. Flag Run Flag Learn Flag By-Pass Flag Man. Flag Reset total Flag Number of Samples per slope calculation = 256 The time between samples is chosen so that you have covered about 60% of the range of the ramp offset 50 for each slope calculation. The ramp offset is reset for each new slope calculation. Thus, the lower the set point the longer it takes to calculate the slope.

The following is a program with descriptive comments for carrying out the basic operations of the computer 56:

__________________________________________________________________________*B*L T/2*T T/2END 177554 OUT = 177554 177552 DATA = 177552 177554 OFFSET = 177554 177550 SET = 177550 177550 LKS = 177550 040200 ONEF = 040200 040400 TWOF = 040400 040700 SIXF = 040700 000004 WAITR = 4 000011 READ = 11 DEFINITIONS OF 000012 WRITE = 12 CONSTANTS, ADDRESSES 000000 R0=%0 AND REGISTERS. 000001 R1 = %1 000002 R2 = %2 000003 R3 = %3 000004 R4 = %4 000005 R5 = %5 000006 R6 = %6 000006 SP = %6 000007 PC = %7 057452 $ADR= 57452 060206 $CMR= 60206 063500 $DVR= 63500 061664 $GCO= 61664 064146 $IR= 64146 LINKS TO FLOATING POINT 064232 $MLR= 64232 MATH PACKAGE (FPMP-WRITTEN 064412 $MLR= 64412 BY D.E.C.) 064772 $NGR= 64772 065146 $POLSH= 65146 060264 $RCl= 60264 065024 $Rl= 65024 057446 $SBR= 57446 000174 .=174000174 050722 .WORD INT SET UP 1KHZ. CLOCK INTERRUPT000176 00340 .WORD 000340 VECTOR 050000 .=50000050000 010767 START: MOV PC, STKST 003642050004 016706 MOV STKST, SP ; STACK POINTER IS 003636 NOW POINTING050010 005746 TST (SP)- TO STKST050012 013700 MOV at #177552, R0 177552050016 052767 BIS #2, SET ;INITIALIZE 000002 OFFSET 127524 VOLTAGE TO050024 012767 MOV #177777,OFFSET ZERO (IN COMPLEMENT FORM 177777 127522 ;INITIALIZE050032 005067 CLR SET CONTROL 127512 VOLTAGE TO RQ at GE 001 ZERO(IN050036 012767 MOV #177777,OFFSET COMPLEMENT FORM) 177777 127510 INITIALIZE050044 000004 IOT TELETYPE050046 000000 .WORD 0 THROUGH050050 002 .BYTE 2,0 IOX (IOX IS WRITTEN BY D.E.C.)050051 000050052 00004 IOT SETS UP050054 050060 .WORD ASK CONTROL P050056 003 .BYTE 3,0 RETURN ADDRESS050057 000050060 012701 ASK: MOV #TABLE1, R1; GET ADDRESS OF TABLE OF - QUESTIONS 050400050064 012767 MOV #9., LOOP; SET UP LOOP FOR NINE QUESTIONS 000011 003552050072 012700 MOV #MTABLE R0; GET ADDRESS OF TABLE CONTAINING POINTERS TO THE 9 QUESTIONS 050356050076 012067 MORE: MOV (R0)+,WBUFFER 000002050102 000004 IOT050104 000000 WBUFFER: .WORD 0 QUESTION050106 012 .BYTE WRITE, 1050107 001050110 000004 IOT050112 050250 .WORD BUFFER GET A REPLY050114 011 .BYTE READ,0050115 000 WAIT UNTIL050116 00004 WAITT: IOT REPLY IS050120 050116 .WORD WAITT GIVEN BY050122 004 .BYTE WAITR,0 OPERATOR AT TTY.050123 000050124 012746 MOV #BUFFER+6, (SP)-; PUT ADDRESS OF REPLY ON STACK 050256050130 016746 MOV BUFFER +4, (SP)-; PUT LENGTH OF REPLY ON STACK 00120050134 162716 SUB #2, (SP) 000002050140 005046 CLR (SP)- FREE FORMAT CONVERSION050142 005046 CLR (SP)-050144 004767 JSR PC, RCP: CONVERT REPLY 050114 TO FLOATING POINT #.050150 032621 MOV (SP)+, (R-)+ STORE REPLY IN050152 033521 MOV (SP)+(R1)+ TABLE 1.050154 005367 DEC LOOP 003464050160 001346 BNE MORE050162 005046 CLR (SP)-050164 012746 MOV #042722, (SP)- PUT FLTING PT. 1680 ON THE STACK 042722 RQ at GE 002050170 012701 MOV #TABLE 1,14, R1 050414050174 014146 MOV (R1)-, (SP)-050176 014146 MOV (R1)-, (SP)- CALCULATE #SAMPLES/SEC.050200 014146 MOV (R1)-, (SP)-050202 014146 MOV (R1)-, (SP)-050204 004467 JSR R4, $POLSH 014736050210 063500 $DVR050212 050214 .WORD .+2050214 011667 MOV (SP), HOLD8 STORE #SAMPLES/ 003450 SEC050220 016667 MOV 2(SP), HOLD9 000002 003444050226 004467 JSR R4, $POLSH DIVIDE SAMPLES/ 014714 SEC BY 1680 TO050232 063500 $DVR GIVE THE # OF050234 065024 $R1 INTERRUPTS PER SAMPLE050236 050240 .WORD .+2050240 012667 MOV (SP)+, INTSAM; STORE RESULT. 003430050244 000167 JMP INIT; GO TO THE INITIALIZATION SECTION 002126050250 000100 BUFFER: 100050252 000000 0 BUFFER FOR050254 000000 0 REPLYS TO QUESTIONS 050356 .=.+100050356 050450 MTABLE: TABLE050360 050472 TABLE2050362 050506 TABLE3050364 050522 TABLE4 POINTERS TO050366 050544 TABLE5 THE QUESTIONS050370 050570 TABLE6050372 050604 TABLE7050374 050630 TABLE8050376 050662 TABLE9 050450 TABLE1: .=.+50050450 000014 TABLE: TABLE2-TABLE-6050452 000000 0050454 000014 TABLE2-TABLE-6 THE QUESTIONS050456 015 .BYTE 15,12050457 012050460 106 .ASCII 'FEED V/S=': VOLTS/SECOND FEED RATE050461 105050462 105050463 104050464 040050465 126050466 057 RQ at GE 003050467 123050470 075 050472 .EVEN050472 000006 TABLE2: TABLE3-TABLE2-6050474 000000 0050476 000006 TABLE3-TABLE2-6050500 124 .ASCII 'TIME='; SMALL SMAPLE TIME IN SECONDS050501 111050502 115050503 105050504 075 050506 .EVEN050506 000006 TABLE3: TABLE4-TABLE3-6050510 000000 0050512 000006 TABLE4-TABLE3-6050514 043 .ASCII '#SAM='; #SAMPLES PER SMALL SAMPLE TIME050515 123050516 101050517 115050520 075 050522 .EVEN050522 000014 TABLE4: TABLE5-TABLE4-6050524 000000 0050526 000014 TABLE5-TABLE4-6050530 105 .ASCII 'ERR BND V/S='; SMALL SAMPLE ERROR BAND IN VOLT/SECOND050531 122050532 122050533 040050534 102050535 116050536 104050537 040050540 126050541 057050542 123050543 075 050544 .EVEN050544 000016 TABLE5: TABLE6-TABLE5-6050546 000000 0050550 000016 TABLE6-TABLE5-6050552 043 .ASCII '#SM SAM/LARGE=' ;#OF SMALL SAMPLES PER LARGE SAMPLE TIME.050553 123050554 115050555 040050556 123050557 101050560 115050561 057050562 114050563 101 RQ at GE 004050564 122050565 107050566 105050567 075 050570 .EVEN050570 000006 TABLE6 TABLE7-TABLE6-6050572 000000 0050574 000006 TABLE7-TABLE6-6050576 105 .ASCII 'ERR K=' OUTPUT ERROR CONTANT "K" THIS IS SYSTEM GAIN.050577 122050600 122050601 040050602 113050603 075 050604 .EVEN050604 000016 TABLE7: TABLE8-TABLE7-6050606 000000 0050610 000016 TABLE8-TABLE7-6050612 043 .ASCII '#SM SAM B4 SW=' ;#OF SMALL SAMPLES BEFORE SWITCHING050613 123050614 115050615 040050616 123050617 101050620 115050621 040050622 102050623 064050624 040050625 123050626 127050627 075 050630 .EVEN050630 000024 TABLE8: TABLE9-TABLE8-6050632 000000 0050634 000024 TABLE9-TABLE8-6050636 123 .ASCII 'STARTUP ERR BND V/S='050637 124050640 101050641 122050642 124050643 125050644 120050645 040050646 105050647 122050650 122050651 040050652 102050653 116 RQ at GE 005050654 104050655 040050656 126050657 057050660 123050661 075 050662 .EVEN050662 000024 TABLE: TABLEZ-TABLE9-6050664 000000 0050666 000024 TABLEZ TABLEZ-TABLE9-6050670 043 .ASCII '#SM SAM IN STARTUP="050671 123050672 115050673 040050674 123050675 101050676 115050677 040050700 111050701 116050702 040050703 123050704 124050705 101050706 122050707 124050710 125050711 120050712 075 050714 .EVEN050714 000 TABLEZ: .BYTE 0 050716 .EVEN050716 000167 LINK: JMP RESET 001212050722 005737 INT: TST #177552; START OF INTERRUPT SERVICE. 117552050726 005367 DEC INTS IS IT TIME TO 002556 SAMPLE?050732 001401 BEQ SAMPLE050734 000002 RT1050736 004767 SAMPLE: JSR PC, SAVE 001366050742 005267 INC SET; START A/D CONVERSION 126602050746 105767 CK: TSTB SET 126576050752 100375 BPL CK050754 016700 MOV DATA, R0; GET THE A/D OUTPUT 126572050760 005100 COM R0 RQ at GE 006050762 016767 MOV INTSA, INTS; RESET # INTERRUPTS/ SAMPLE. 002524 002520 IS THE A/D OUT-050770 022700 CMP #980., R0 PUT GREATER THAN 001724 9 VOLTS? IF YES RESET.050774 003750 BLE LINK050776 060067 ADD R0, Y+2 SUM THE Y VALUE 002514 FOR THE051002 005567 ADC Y REGRESSION. 002506051006 016701 MOV X, R1 MULTIPLY THE X 002506 BY THE Y051012 004767 JSR PC,MULTY 001062051016 060167 ADD R1,XY+2 002514 SUM THE XY VALUE051022 005567 ADC XY FOR THE 002506 REGRSSSION.051026 060067 ADD R0,XY 002502051032 005367 DEC X; REDUCE X VALUE BY 1 002462051036 001402 BEQ CALC; IF X=O IT IS TIME TO CALCULATE THE SLOPE051040 004767 JSR PC,RESTORE 001312051044 016767 CALC: MOV N,X; RESET THE X VALUE 002500 002446051052 016767 MOV Y,YC 002436 STORE THE 002464 .SIGMA.Y051060 016767 MOV Y+2,YC+2 002432 002460051066 016767 MOV XX,XYC 002442 STORE THE .SIGMA.X 002444051074 016767 MOV XY+2,XYC+2 002436 002440051102 005067 CLR XY 002426051106 005067 CLR XY+2 RESET .SIGMA.XY AND 002424 .SIGMA.Y FOR NEXT051112 005067 CLR Y SAMPLE PERIOD. 002376051116 005067 CLR Y+2 002374051122 016746 MOV N1+2,(SP)- 002426 PUT # SAMPLES RQ at GE 007 ON THE STACK.051126 016746 MOV N1, (SP)- 002420051132 016700 MOV XYC, R0 002402051136 016701 MOV XYC+2,R1 002400 CONVERT .SIGMA.XY TO051142 004767 JSR PC,DFLOAT A FLOATING POINT 000620 # AND PUT IT ON051146 004467 JSR R4,$POLSH THE STACK. 013774051152 064412 SMLR (#SAMPLES) .times.051154 051156 .WORD .+2 .SIGMA.XY051156 016746 MOV X1+2,(SP)- 002350 PUT X ON051162 016746 MOV X1,(SP)- STACK 002342051166 016700 MOV YC, R0 CONVERT .SIGMA.Y TO 002352 MOV YC+2,R1 FLOATING POINT051172 016701 AND PUT IT ON 002350 JSR PC,DFLOAT THE STACK.051176 004767 000564051202 004467 JSR R4,$POLSH 013740 GET (#SAMPLES)051206 064412 $MLR (.SIGMA. XY).SIGMA.X.SIGMA.Y051210 057446 $SBR051212 051214 .WORD .+2051214 016746 MOV N1+2, (SP)- PUT #SAMPLES 002334 ON THE STACK.051220 016746 MOV N1, (SP)- 002326051224 016746 MOV X2+2,(SP)- PUT.SIGMA.X.sup.2 ON 002276 STACK.051230 016746 MOV X2, (SP)- 002270051234 004467 JSR R4,$POLSH GET (#SAMPLES) 013706 (.SIGMA.X.sup.2)051240 064412 $MLR051242 051244 .WORD .+2051244 016746 MOV X1+2,(SP)- PUT .SIGMA.X ON 002262 STACK.051250 016746 MOV X1,(SP)- 002254051254 016746 MOV X1+2,(SP)-; .SIGMA.X ON STACK AGAIN 002252051260 016746 MOV X1,(SP)- 002244051264 004467 JSR R4,$POLSH 013656051270 064412 $MLR RQ at GE 010 ##STR1##051272 057446 $SBR SLOPE051274 063500 $DVR051276 064772 $NGR051300 051302 .WORD .+2051302 016746 MOV SAMS01+2,(SP)- PUT #SAMPLES/ 002252 SECOND ON051306 016746 MOV SAMS01,(SP)- STACK 002244051312 004467 JSR R4,$POLSH 013630051316 064412 $MLR051320 051322 .WORD .+2051322 005046 CLR (SP)-051324 012746 MOV #041710,(SP)-; FLOATING POINT 100 041710051330 004467 JSR R4,$POLSH 013612051334 063500 $DVR; ##STR2##051336 051340 .WORD .+2051340 011667 MOV (SP),TEMP STORE V/S FOR 002216 LATER USE.051344 016667 MOV 2(SP),TEMP+2 000002 002212051352 016746 MOV PREV+2,(SP)- PUT PREVIOUS 002212 V/S ON STACK051356 016746 MOV PREV,)SP)- 002204051362 004467 JSR R4,$POLSH PREV-CURRENT 051360 V/S.051366 057446 $SBR051370 051372 .WORD .+2051372 032716 BIT #100000,(SP) 100000 GET THE051376 001404 BEQ OVR ABSOLUTE VALUE051400 004467 JSR R4, $POLSH .vertline.PREV V/S- 013542 CURRENT V/S.vertline.051404 064772 $NGR051406 051410 .WORD .+2051410 005767 OVR: TST ERRSW LARGE OR SMALL 002156 ERROR BAND?051414 001410 BEQ LARGE051416 005367 DEC ERRSW-SMALL- DECREASE #SMALL SAMPLES BEFORE SWITCHING ERROR bands. 002150051422 001405 BEQ LARGE051424 016746 MOV SE+2,(SP)- MOVE SMALL 002150 ERROR BAND051430 016746 MOV SE,(SP)- ONTO STACK. 002142051434 000404 BR TSTE; TEST FOR ACRILOK RQ at GE 011051436 016746 LARGE: MOV LE+2,(SP)- MOVE LARGE 002142 ERROR BAND051442 016746 MOV LE,(SP)- ONTO STACK. 002154051446 004467 TSTE: JSR R4, $POLSH COMPARE 013474 .vertline.PREV V/S-051452 060206 $CMR CURRENT V/S.vertline.051454 051456 .WORD .+2 TO ALLOWABLE051456 003402 BLE .+ 6 ERROR IN V/S051460 000167 JMP ACRILOCK AND JMP IF TOO LARGE. 000630051464 016767 MOV TEMP,PREV; THIS IS .+6 002072 YOU ARE WITHIN 002074 THE ERROR BAND051472 016767 MOV TEMP+2,PREV+2 (STORE THE FEED 002066 RATE IN V/S 002070051500 005267 INC UPDAT; SET THE FLAG TO INDICATE A NEW FEED RATE HAS JUST BEEN CALCULATED 002002051504 005767 TST LOS ARE WE USING 002102 LARGE OR SMALL051510 001451 BEQ LAR SAMPLES?051512 005367 DEC LOS: DECREMENT # OF SMALL SAMPLES. 002074051516 016746 UPDATE: MOV K+2,(SP)- PUT OUTPUT 002076 CONSTANT051522 016746 MOV K, (SP)- (SYSTEM GAIN) ON THE STACK. 002070051526 016746 MOV FR +2 (SP)- PUT DESIRED 002072 FEED RATE ON051532 016746 MOV FR, (SP)- THE STACK. 002064051536 016746 MOV PREV+2, (SP)- PUT CURRENT 002026 FEED RATE ON051542 016746 MOV PREV,(SP)- THE STACK. 002020051546 004467 JSR R4, $POLSH 013374051552 057446 $SBR (CURRENT-DESIR- -051554 064412 $SMLR ED)K + CONWOR051556 065024 $RI PREVIOUS MOTOR051560 051562 .WORD .+2 SPEED.051562 062667 ADD (SP)+,CONWOR 002040051566 026727 CMP CONWAR,#2000 IF RESULT IS 002034 GREATER THAN 002000 2000 (6Vat051574 100403 BMI CNTU OUTPUT OF D/A)051576 012767 MOV#1777,CONWOR MAKE IT=2000; I.E., LIMIT 001777 RESULT TO 6 VOLTS 002022 RQ at GE 012051604 042767 CNTU: BIC#02,SET; GET SET TO UPDATE MOTOR SPEED. 000002 125736051612 005167 COM CONWOR THE D/A USES 002010 NEGATIVE LOGIC.051616 016767 MOV CONWOR, OUT 002004 125730051624 005167 COM CONWOR; BUT THE PROGRAMMER PREFERS TO THINK POSITIVE. 001776051630 004767 JSR PC,RESTORE; GO BACK TO WHERE YOU WERE BEFORE BEING RUDELY INTERRUPTED. 000522051634 016746 LAR: MOV PREV+2,(SP)- 001730 IF YOU ARE051640 016746 MOV PREV,(SP)- CALLING FOR 001722 LARGE SAMPLES,051644 016746 MOV AVG+2,(SP)- I.E. AN AVERAGE 001762 OF THE V/S051650 016746 MOV AVG, (SP)- CALCULATIONS, 001754 THEN YOU ARE051654 004467 JSR R4,$POLSH HERE. COMPUTE 013266 THE RUNNING051660 057452 $ADR AVERAGE.051662 051664 .WORD .+2051664 005767 TST SSLST 001744 IF YOU HAVE051670 001411 BEQ CALL ENOUGH V/S051672 005367 DEC SSLST CALCULATIONS 001736 USE THE051676 001406 BEQ CALL AVERAGE;I.E. JUMP TO CALL.051700 012667 MOV (SP)+,AVG. YOU DON'T HAVE 001724 ENOUGH V/S051704 012667 MOV (SP)+,AVG+2 CALCULATIONS. 001722 RETURN TO WHERE051710 004767 JSR PC,RESTORE YOU WERE BEFORE THE INTERRUPT. 000442051714 016767 CALL: MOV RESET RESET # SMALL 001716 SAMPLES PER 001712 LARGE SAMPLE051722 016746 MOV SSLSTR+2,(SP)- TIME. 001714051726 016746 MOV SSLSTR,(SP)-; PUT # SMALL SAMPLES/LARGE SAM ON STACK. 001706051732 004467 JSR R4,$POLSH GET THE AVER. 013210 OF THE SMALL051736 063500 $DVR SAMPLES COM-051740 051742 .WORD .+2 PRISING THE LARGE SAMPLE.051742 012667 MOV (SP)+,PREV 001620 STORE THE051746 012667 MOV (SP)+,PREV+2 AVERAGE. 001616 RQ at GE 013051752 005067 CLR AVG 001652 RESET THE AVG.051756 005067 CLR AVG+2 001650051762 000167 JMP UPDATE; REFRESH THE MOTOR SPEED. 177530051766 012667 DEFLOAT: MOV (SP)+,RTRN 000104051772 005046 CLR (SP)-051774 005046 CLR -(SP)051776 005700 TST R0052000 003007 BGT POS27052002 002403 BLT OVE27052004 005701 TST R1052006 001432 BEQ ZER27052010 000403 BR POS27052012 005401 OVE27: NEG R1052014 005400 NEG R0052016 005601 SBC R1052020 006146 POS27: ROL -(SP)052022 000241 CLC052024 012702 MOV #240,R2 000240052030 006101 NOM 27: ROL R1052032 006100 ROL R0052034 103402 BCS NOD27 DOUBLE052036 005302 DEC R2 PRECISION052040 000773 BR NOM27 INTEGER TO052042 000301 NOD27: SWAB R1 FLOATING POINT052044 110166 MOVB R1,4(SP) SUBROUTINE 000004052050 110066 MOVB R0,5(SP) 000005052054 105000 CLRB R0052056 150200 BISB R2,R0052060 000300 SWAB R0052062 006026 ROR (SP)+052064 006000 ROR R0052066 006066 ROR 2(SP) 000002052072 010016 MOV R0,atSP052074 000137 ZER27: JMP at(PC)+052076 000000 RTRN: 0052100 005002 MULTY: CLR R2 INTEGER MULTIPLY052102 005004 CLR R4 SUBROUTINE052104 012703 MOV #16., R3 16BIT .times. 16BIT= 000020 32 BIT RESULT.052110 006200 ASR R0052112 103001 MR: BCC .+4052114 060102 ADD R1,R2 RQ at GE 014052116 006002 ROR R2052120 006000 ROR R0052122 005303 DEC R3052124 001372 BNE MR052126 010001 MOV R0,R1052130 010200 MOV R2,R0052132 000207 PTS PC052134 052767 RESET. BIS#2,SET WHEN A/D OUTPUT 000002 RAMPS GREATER 125406 THAN 9V LIMIT052142 062767 ADD#17,OFFDAC RESET IT CLOSE 000017 TO ZERO BY 000136 CHANGING THE052150 016767 MOV OFFDAC,OFFSET OFFSET VALUE & 000132 COMPARING, 125376 LOOPING. NOTE052156 012767 MOV#24150,LOOP1;90 MILLISEC THE RESPONSE 024150 TIME OF 90 000124 MILLISEC FOR052164 005367 A:DEC LOOP1 LARGE STEPS, & 000120 WHEN YOU GET052170 001375 BNE A CLOSE TO ZERO,052172 062767 RESETA:ADD#1,OFFDAC RESPONSE TIME 000001 OF 5 MILLI- 000106 SECONDS.052200 016767 MOV OFFDAC,OFFSET 000102 125346052206 012767 MOV#4440,LOPP1; 5MILLISEC 004440 000074052214 005367 B: DEC LOOP1 000070052220 001375 BNE B052222 005267 INC SET 125322052226 105767 WATHO: TSTB SET 125316052232 100375 BPL WATHO052234 026727 CMP DATA,#177631 125312 177631052242 100001 BPL CONTIN052244 000752 BR RESETA052246 016767 CONTIN: MOV N,X 001276 001244052254 016767 MOV INTSA,INTS; RESET # INTER- RUPTS/SAMPLE 001232 001226 RQ at GE 015052262 005067 CLR Y 001226 ZERO THE SUMS;052266 005067 CLR Y+2 THROW OUT THIS 001224 SAMPLE PERIOD052272 005067 CLR XY DUE TO THE 001236 NEED FOR RE-052276 005067 CLR XY+2 SETTING. - 001234052302 004767 JSR PC,RESTORE; RETURN TO PREVIOUS TASK. 000050052306 000000 OFFDAC: 0052310 000000 LOOP1: 0052312 000000 HPREMP: HALT; IF HOPPER IS EMPTY HALT.052314 005267 ACRILOCK: INC ACRILK 001266 SET ACRILOCK052320 005267 INC UPDAT FLAG. 001162052324 004767 JSR PC,RESTORE 000026052330 012667 SAVE: MOV (SP)+, SAV 000016052334 010046 MOV R0,(SP)-052336 010146 MOV R1,(SP)-052340 010246 MOV R2,(SP)- SAVE SUBROUTINE052342 010346 MOV R3,(SP)-052344 010446 MOV R4,(SP)-052346 010546 MOV R5,(SP)-052350 000137 JMP AT(PC)+052352 000000 SAV: 0052354 000000 SAV1: 0052356 005726 RESTORE: TST (SP)+052360 012605 MOV (SP)+,R5052362 012604 MOV (SP)+,R4052364 012603 MOV (SP)+,R3 RESTORE052366 012602 MOV (SP)+,R2 SUBROUTINE.052370 012601 MOV (SP)+,R1052372 012600 MOV (SP)+,R0052374 000002 RTI052376 016746 INIT: MOV TABLE1+12,(SP)-; # SAMPLES YOU COME HERE 176010 AFTER ANSWERING QUESTIONS TO052402 016746 MOV TABLE1+10,(SP)- ESTABLISH A NEW SET OF 176002 OPERATING PARAMETERS.052406 004467 JSR R4,$POLSH 012534052412 065024 $RI052414 052416 .WORD .+2052416 012667 MOV (SP)+,HOLD INTEGER # SAMPLES. 001226052422 016746 MOV TABLE1+12,(SP)- 175764 RQ at GE 016052426 016746 MOV TABLE1+10,(SP)- 175756052432 016746 MOV TABLE 1+12,(SP)- 175754 CALCULATE NEW052436 016746 MOV TABLE1+10, (SP)- ##STR3## 175746052442 005046 CLR (SP)-052444 012746 MOV #ONEF,(SP)- 040200052450 004467 JSR R4,$POLSH 012472052454 057452 $ADR052456 064412 $MLR052460 052462 WORD .+2052462 005046 CLR (SP)-052464 012746 MOV #TWOF,(SP)- 040400052470 004467 JSR R4, $POLSH 012452052474 063500 $DVR052476 052500 .WORD .+2052500 012667 MOV (SP)+,HOLD1 PUT IT IN 001146 STORAGE052504 012667 MOV (SP)+,HOLD2 001144052510 005046 CLR (SP)-052512 012746 MOV #ONEF,(SP)- 040200052516 016746 MOV TABLE1+12,(SP)- 175670052522 016746 MOV TABLE1+10,(SP) 175662052526 005046 CLR (SP)-052530 012746 MOV #TWOF,(SP)- 040400052534 004467 JSR R4,$POLSH 012406052540 064412 $MLR052542 057452 $ADR052544 052546 .WORD .+2 CALCULATE NEW05246 016746 MOV TABLE1+12 (SP)- ##STR4## 175640052552 016746 MOV TABLE1+10,(SP)- 175632052556 016746 MOV TABLE1+12,(SP)- 175630052562 016746 MOV TABLE1+10,(SP)- 175622052566 005046 CLR (SP)-052570 012746 MOV #ONEF,(SP)- 040200 RQ at GE 017052574 004467 JSR R4,$POLSH 012346052600 057452 $ADR052602 064412 $MLR052604 064412 $MLR052606 052610 .WORD .+2052610 005046 CLR (SP)-052612 012746 MOV #SIXF,(SP)- 040700052616 004467 JSR R4,$POLSH 012324052622 063500 $DVR052624 052626 .WORD .+2052626 012667 MOV (SP)+,HOLD3 PUT IT IN 001024 STORAGE052632 012667 MOV (SP)+,HOLD4 001022052636 016746 MOV TABLE1+42,(SP)- 175600 CONVERT NEW052642 016746 MOV TABLE1+40,(SP)- # SMALL 175572 SAMPLES BE-052646 004467 JSR R4,$POLSH FORE SWITCH- ING ERROR 012274 BANDS & CONVERT TO052652 065024 $RI INTEGER052654 052656 .WORD .+2052656 012667 MOV (SP)+,HOLD5; PUT IT IN STORAGE 001000052662 016746 MOV TABLE1+22,(SP)- 175534 CONVERT NEW052666 016746 MOV TABLE1+20,(SP)- #SMALL 175526 SAMPLES PER052672 004467 JSR R4,$POLSH LARGE SAMPLE 012250 & CONVERT TO052676 065024 $RI INTEGER.052700 052702 .WORD .+2052702 012667 MOV (SP)+,HOLD6; PUT IT IN STORAGE 000756052706 016746 MOV TABLE1+32,(SP)- CONVERT NEW # 175520 SMALL SAMPLES052712 016746 MOV TABLE1+30,(SP)- BEFORE SWITCH- 175512 ING TO LARGE052716 004467 JSR R4,$POLSH SAMPLES & 012224 CONVERT TO052722 065024 $RI INTEGER.052724 052726 .WORD .+2052726 012667 MOV (SP)+,HOLD7; PUT IT IN STORAGE 000734052732 005067 CLR LKS; TURN OFF THE REAL TIME CLOCK 124612052736 005067 CLR XY 000572 RQ at GE 020 ZERO THE052742 005067 CLR XY+2 SUMS. 000570052746 005067 CLR Y 000542052752 005067 CLR Y+2 000540052756 016767 MOV HOLD8,SAMS01 000706 00572052764 016767 MOV HOLD9,SAMS01+2 000702 000566052772 016767 MOV HOLD7,LOS 000670 000612053000 016767 MOV HOLD6,SSLST 000660 000626053006 016767 MOV HOLD5,ERRSW 000650 000556053014 016767 MOV HOLD4,X2+2 000640 000504053022 016767 MOV HOLD3,X2 000630 000474053030 016767 MOV HOLD2,X1+2 000620 000474053036 016767 MOV HOLD1,X1053044 016767 MOV HOLD,N 000600 000476053052 016767 MOV SSLST,SSLSTI 000556 000556053060 016767 MOV N,X 000464 000432053066 016767 MOV TABLE1,FR 175306 000526 MOVE THE NEW053074 016767 MOV TABLE1+2,FR+2 PARAMETERS INTO 175302 REAL TIME 000522 VARIABLES053102 016767 MOV TABLE1+10,N1 DURING THE 175302 TIME WHEN THE 000442 CLOCK IS OFF RQ at GE 021 SO THAT THE053110 016767 MOV TABLE1+12,N1+2 TRANSITION 175276 DOES NOT OCCUR 000436 IN THE MIDDLE053116 016767 MOV TABLE1+14,SE OF A SAMPLE 175272 PERIOD. 000452053124 016767 MOV TABLE1+16,SE+2 175266 000446053132 016767 MOV TABLE1+34,LE 175276 000442053140 016767 MOV TABLE1+36LE+2 175272 000436053146 016767 MOV TABLE1+24,K 175252 000442053154 016767 MOV TABLE1+26,K+2 175246 000436053162 016767 MOV INTSAM,INTSA 000506 000322053170 016767 MOV INTSA,INTS 000316 000312053176 016767 MOV TABLE1+20SSLSTR 175216 000434053204 016767 MOV TABLE1+22SSLSTR+2 175212 000430053212 005067 CLR AVG 000412 ZERO AVG.053216 005067 CLR AVG+2 000410053222 016706 MOV STKST,SP RESET THE 000420 STACK053226 005746 TST (SP)-053230 052767 BIS #40,LKS; TURN ON THE REAL TIME CLOCK. 000040 124312053236 005767 TEST: TST UPDAT; HAS A NEW FEEDRATE BEEN CALCULATED? 000244053242 001003 BNE NEWDAT; YES PRINT IT053244 000001 WAIT; NO-WAIT FOR INTERRUPT.053246 000167 JMP TEST; RETURN HERE FROM INTERRUPT. 177764053252 005267 NEWDAT: INC CR 000160 RQ at GE 022053256 005767 TST ACRILK 000324053262 001407 BEQ AB053264 016767 MOV TEMP,TEM 000272 000210053272 016767 MOV TEMP+2,TEM+2 000266 000204053300 000406 BR ABC053302 016767 AB: MOV PREV,TEM 000260 000172053310 016767 MOV PREV+2,TEM+2 000254 000166053316 005067 ABC: CLR UPDAT 000164053322 012746 MOV #BUFF,(SP)- 053456053326 012746 MOV #14.,(SP)- 000016053332 012746 MOV #5,(SP)- 000005053336 005046 CLR (SP)-053340 016746 MOV TEM+2,(SP)- 000140053344 016746 MOV TEM,(SP)- 000132053350 004767 JSR PC,$GCO 006310053354 005767 TST ACRILK 000226053360 001405 BEQ AC053362 012767 MOV #'*,BUFF PRINT OUT 000052 NEW FEED 000066 RATE ON TTY;053370 005067 CLR ACRILK 5 PRINTOUTS 000212 PER LINE, WITH053374 022767 AC: CMP #5,CR * IF IN 000005 ACRILOK. 000034053402 001005 BNE OUT!053404 005067 CLR CR 000026053410 000004 10T053412 053440 .WORD CRLF053414 012 .BYTE WRITE,1053414 001053416 000004 OUT!: 10T RQ at GE 023053420 053450 .WORD BBUFF053422 012 .BYTE WRITE,1053423 001053424 000004 WAIT: IOT053426 053424 .WORD WAIT053430 004 .BYTE WAITR,1053431 001053432 000167 JMP TEST 177600053436 000000 CR:0053440 000002 CRLF: 2053442 000000 0053444 000002 2053446 015 .BYTE 15,12053447 012053450 000016 BBUFF: 14.053452 000000 0053454 000016 14. 053502 BUFF: .=.+20. 053506 TEM: .=.+4053506 000000 UPDAT: 0053510 000000 INTS: 0053512 000000 INTSA: 0053514 000000 Y: 0,0053516 000000053520 000000 X: 0,0053522 000000053524 000000 X2: 0,0053526 000000053530 000000 X1: 0,0053532 000000053534 000000 XY: 0,0053536 000000053540 000000 XYC: 0,0053542 000000053544 000000 YC: 0,0053546 000000053550 000000 N: 0053552 000000 N1: 0,0053554 000000053556 000000 SAMS01: 0,0053560 000000 LOCATIONS053562 000000 TEMP: 0,0 FOR053564 000000 VARIABLES,053566 000000 PREV: 0,0 FLAGS,053570 000000 AND053572 000000 ERRSW: 0,0 BUFFERS053574 000000053576 000000 SE: 0,0053600 000000 RQ at GE 024053602 000000 LE: 0,0053604 000000053606 000000 ACRILK: 0,0053610 000000053612 000000 LOS: 0,0053614 000000053616 000000 K: 0,0053620 000000053622 000000 FR: 0,0053624 000000053626 000000 CONWOR: 0053630 000000 AVG: 0,0053632 000000053634 000000 SSLST: 0053636 000000 SSLST1: 0053640 000000 SSLSTR: 0,0053642 000000053644 000000 LOOP: 0053646 000000 STKST: 0053650 000000 HOLD:053652 000000 HOLD1: 0053654 000000 HOLD2: 0053656 000000 HOLD3:053660 000000 HOLD4: 0053662 000000 HOLD5: 0053664 000000 HOLD6: 0053666 000000 HOLD7: 0053670 000000 HOLD8: 0053672 000000 HOLD9: 0053674 000000 INTSAM: 0 000001 .END RQ at GE 025__________________________________________________________________________ __________________________________________________________________________symbol table listinga 052164 ab 053302 abc 053316 ac 053374acrilk 053606 acrilo 052314 ask 050060 avg 053630b 052214 bbuff 053450 buff 053456 buffer 050250calc 051044 call 051714 ck 050746 cntu 051604contin 052246 conwor 053626 cr 053436 crlf 053440data = 177552 dfloat 051766 errsw 053572 fr 053622hold 053650 hold1 053652 hold2 053654 hold3 053656hold 4 053660 hold5 053662 hold6 053664 hold7 053666hold8 053670 hold9 053672 hpremp 052312 init 052376int 050722 ints 053510 intsa 053512 intsam 053674k 053616 lar 051634 large 051436 le 053602link 050716 lks = 177550 loop 053644 loop1 052310los 053612 more 050076 mr 052112 mtable 050356multy 052100 n 053550 newdat 053252 nod27 052042nom27 052030 n1 053552 offdac 052306 offset = 177554onef = 040200 out 177554 out1 053416 over27 052012ovr 051410 pc =%000007 pos27 052020 prev 053566read = 000011 reset 052134 reseta 052172 restor 052356rtrn 052076 r0 =%000000 r1 =%000001 r2 =%000002r3 =%000003 r4 =%000004 r5 =%000005 r6 =%000006sample 050736 sams01 053556 sav 052352 save 052330sav1 052354 se 053576 set = 177550 sixf = 040700sp =%000006 sslst 053634 sslstr 053640 sslst1 053636start 050000 stkst 053646 table 050450 tablez 050714table1 050400 table2 050472 table3 050506 table4 050522table5 050544 table6 050570 table7 050604 table8 050630table9 050662 tem 053502 temp 053562 test 053236tste 051446 twof = 040400 updat 053506 update 051516wait 053424 waitr = 000004 waitt 050116 watho 052226wbuffe 050104 write = 000012 x 053520 xy 053534xyc 053540 x1 053530 x2 053524 y 053514yc 053544 zer27 052074 $adr = 057452 $cmr = 060206$dvr = 063500 $gco = 061664 $ir = 064146 $mli = 064232$mlr = 064412 $ngr = 064772 $polsh = 065146 $rci = 060264$ri = 065024 $sbr = 057446 . = 053676000000 errors__________________________________________________________________________ *s

from the foregoing disclosure, it can be seen that the instant invention provides an improved weigh feeding apparatus, wherein the discharge rate of a substance from a container may be maintained at a preselected constant value, wherein the container may be automatically refilled during the continuous discharge of the substance, wherein excessive excursions of the system are eliminated, wherein extraneous data recordings are eliminated when calculating the flow rate, and wherein past flow rate values may be stored in memory and compensated for at a later point in time.

Although a certain particular embodiment of the invention has been herein disclosed for purposes of explanation, various modifications thereof, after study of the specification, will be apparent to those skilled in the art to which the invention pertains.

Claims

1. A weigh feeding apparatus comprising a container for a prefilled substance, means for discharging said substance from said container at a controllable rate; means for weighing said container prefilled with said substance; means coupled to said weighing means for producing a first electrical signal proportional in amplitude to the weight determined by said weighing means; high gain amplifier means for amplifying said first electrical signal, an analog-digital converter coupled to said amplifier means, digital computer means coupled to said analog-digital converter for computing and outputting a signal corresponding to the signal received, digital-analog converter ramp offset means controlled by said computer output signal, having a controlled stepping output applied as a second input signal to said amplifier means to algebraically combine with said first electrical signal, each step corresponding to one time cycle of operation thereby to maintain the output of said amplifier in a given preselected range of amplitude during said one time cycle of operation, said computer means being adapted to compute a corrective signal based on said signal received, and means coupled between said computer means and said means for discharging said substance from said container for controlling the rate of discharge responsive to said corrective signal.

2. A weigh feeding apparatus according to claim 1 further comprising means for inputting into said computer means a preselected feed rate, said computer means being adapted to store in memory a series of said signals received from said analog-digital converter for each of said time cycles of operation and computing said corrective signal by comparing said signals received with said preselected feed rate.

3. A weigh feeding apparatus according to claim 2 wherein said computer means is adapted to maintain said corrective signal constant during the time when a preselected number of said signals received from said analog-digital converter exceeds preselected upper or lower limits, during one time cycle of operation.

4. A weigh feeding apparatus according to claim 2 wherein said computer means is further adapted to compute said corrective signal disregarding a preselected number of said signals received from said analog-digital converter exceeding preselected upper or lower limits, during one time cycle of operation, when computing said corrective signal.

5. A weigh feeding apparatus according to claim 2 further comprising means for correcting said signal received to compensate for errors due to extraneous noise.

6. A weigh feeding apparatus according to claim 5 wherein said means for correcting said signal received includes shaft encoder means coupled between said means for discharging said substance from said container and said digital computer means.

7. A weigh feeding apparatus comprising a container for a prefilled substance, means for discharging said substance from said container at a controllable rate; means for weighing said container prefilled with said substance; means coupled to said weighing means for producing a first electrical signal proportional in amplitude to the weight determined by said weighing means; first amplifier means for amplifying said first electrical signal, a first analog-digital converter coupled to said first amplifier means, digital computer means coupled to said first analog-digital converter for computing a first output signal corresponding to the weight of said substance in said container, second amplifier means for amplifying the signal received from said first amplifier means, a second analog-digital converter coupled to said second amplifier means, said digital computer means being coupled to said second analog-digital converter, said couputer means being adapted to compute a corrective signal based on said signal received from said second analog-digital converter, and means coupled between said computer means and said means for discharging said substance from said container for controlling the rate of discharge responsive to said corrective signal.

8. A weigh feeding apparatus according to claim 7 further comprising under-weight limit input means to said computer means, and over-weight limit input means to said computer means, said computer means being adapted to actuate alarm means when said signals received from said first analog-digital converter exceed one of said limits.

9. A weigh feeding apparatus according to claim 7 further comprising means for inputting into said computer means a preselected feed rate, said computer means being adapted to integrate said preselected feed rate with respect to time and output a display corresponding to the desired total feed commanded, said computer means being further adapted to integrate the actual total weight of material fed as determined by the signal received from said first analog digital converter means and, by comparing said total feed commanded to said actual total weight of material fed, adjust said corrective signal.

10. A weigh feeding apparatus according to claim 7 further comprising means for inputting into said computer means a preselected feed rate, said computer means being adapted to store in memory a series of said signals received from said second analog-digital converter means for each of said time cycles of operation and compute said corrective signal by comparing said signals received with said feed rate; electrically actuated means for refilling said container, means for inputting into said computer means a preselected low level of value corresponding to the desired minimum level of substance in said container; means for inputting into said computer means a preselected out of low level value corresponding to the desired maximum level of substance in said container; said computer means being adapted to compare the actual weight of substance in said container as determined by the signal received from said first analog-digital converter means with the preselected low level value and when said values coincide search said corrective signal until said corrective signal is within preselected deviation limits, and when the corrective signal is within said preselected limits, acutating said means for refilling said container while maintaining said corrective signal constant, and when the actual weight of sbustance in said container as determined by the signal received from said first analog-digital converter reaches said preselected out of low level value, said means for refilling said container being disengaged and said corrective signal being again actuated.

11. A weigh feeding apparatus according to claim 7 wherein said means for discharging said substance from said container comprises an electric motor, means interconnecting said motor with said computer means to input into said computer means the rotational speed of said motor, and input means to said computer means to preselect a desired rotation speed of said motor, switching input means for said computer means to selectively control said corrective signal by comparing the actual motor speed with the desired motor speed.

12. A weigh feeding apparatus comprising a container for a prefilled substance, means for discharging said substance from said container at a controllable rate; means for weighing said container prefilled with said substance; means coupled to said weighing means for producing a first electrical signal proportional in amplitude to the weight determined by said weighing means; first amplifier means for amplifying said first electrical signal, a first analog-digital converter coupled to said first amplifier means, digital computer means coupled to said first analog-digital converter for computing a first output signal correspnding to the weight of said substance in said container, second amplifier means for amplifying the signal received from said first amplifier means, a second analog-digital converter coupled to said second amplifier means, said digital computer means being coupled to said second analog-digital converter for computing and outputting a signal corresponding to the input signal received from said second analog-digital converter, digital-analog converter ramp offset means, controlled by said second computer output signal, having a controlled stepping output applied as a second input signal to said second amplifier means to algebraically combine with said input to said second amplifier means form said first amplifier means, each step corresponding to one time cycle of operation thereby to maintain the output of said second amplifier in a given preselected range of amplitude during said one time cycle of operation, said computer means being adapted to compute a corrective signal based on said signal received from said second analog-digital converter, and means coupled between said computer means and said means for discharging said substance from said container for controlling the rate of discharge responsive to said corrective signal.

13. A weigh feeding apparatus according to claim 12 further comprising means for inputting into said computer means a preselected feed rate value, said computer means being adapted to store in memory a series of said signals received from said second analog-digital converter for each of said time cycles of operation and computing said corrective signal by comparing said signals received with said preselected feed rate value.

14. A weigh feeding apparatus according to claim 12 wherein the output from said first amplifier means ranges between about -10 volts when the container is full to about +10 volts when the container is empty.

15. A weigh feeding apparatus according to claim 12 wherein the output from said second amplifier means ranges between about +5 volts and -5 volts during one time cycle of operation.

16. A weigh feeding apparatus comprising container means, means for discharging a substance from said container means at a controllable rate, means for detecting the weight of the substance being discharged from said container means, means coupled to said detecting means for producing electrical signals proportional to the weight determined by said detecting means, an analog-digital converter for receiving said electrical signals, digital computer means coupled to said analog-digital converter for computing a corrective signal based on the signals received, means coupled between said computer means and said means for discharging said substance from said container for controlling the rate of discharge responsive to the corrective signal, means for inputting into said computer means a preselected feed rate, said computer means being adapted to store a series of the signals received from said analog-digital converter for a time cycle of operation and computing said corrective signal by comparing said signals received with said preselected feed rate, said computer means being adapted to maintain said corrective signal constant during the time when a preselected number of said signals received from said analog-digital converter exceeds preselected upper or lower limits, during one time cycle of operation.

17. A weigh feeding apparatus according to claim 16 wherein said computer means is further adapted to compute said corrective signal disregarding a preselected number of said signals received from said analog-digital converter exceeding preselected upper or lower limits, during one time cycle of operation, when computing said corrective signal.

18. A weigh feeding apparatus according to claim 16 further comprising means for correcting said signal received to compensate for errors due to extraneous noise.

19. A weigh feeding apparatus according to claim 16 wherein said means for correcting said signal received includes shaft encoder means coupled between said means for discharging said substance from said container and said digital computer means.

20. A weigh feeding apparatus comprising a container for prefilling with a substance, means for discharging said substance from said container at a controllable rate, means for weighing said container prefilled with said substance, means coupled to said weighing means for producing electrical signals proportional to the weight determined by said weighing means, an analog-digital converter for receiving said electrical signals, digital computer means coupled to said analog-digital converter for computing a corrective signal based on the signals received, means coupled between said computer means and said means for discharging said substance from said container for controlling the rate of discharge responsive to the corrective signal, means for inputting into said computer means a preselected feed rate, said computer means being adapted to store a series of the signals received from said analog-digital converter for a time cycle of operation and computing said corrective signal by comparing said signals received with said preselected feed rate, said computer means being adapted to maintain said corrective signal constant during the time when a preselected number of said signals received from said analog-digital converter exceeds preselected upper or lower limits, during one time cycle of operation.