Electronically controlled beverage dispenser

Information

  • Patent Grant
  • 6449966
  • Patent Number
    6,449,966
  • Date Filed
    Tuesday, October 28, 1997
    27 years ago
  • Date Issued
    Tuesday, September 17, 2002
    22 years ago
Abstract
An electronic control for the operation of a beverage dispenser of the refrigerated ice bank type is shown. The control provides for reliable determinations of when ice production is needed and when it is not needed. A microprocessor receives information from an ice bank probe and from a temperature probe located within the ice bank. Data collected by the microprocessor from both the ice bank probe and the temperature probe is used to determine if the ice bank is either insufficient in size and should be increased or is of sufficient size such that the compressor can be turned off. A carbonator level probe is also shown and connected to the microprocessor. The microprocessor is programmed whereby the carbonator probes are sampled in a manner to accurately determine the level of water in the carbonator and therefore the need for turning on or turning off any water pump connected thereto Both the operation of the compressor and the water pump are controlled by the microprocessor wherein the programming thereof provides for adequate hysteresis protection so that short cycling of the compressor and water pump is avoided.
Description




FIELD OF THE INVENTION




The present invention relates to beverage dispensers and in particular electronically controlled beverage dispensers of the ice bank type.




BACKGROUND OF THE INVENTION




Beverage dispensers are well known in the art and are typically used to dispense carbonated beverages consisting of a combination of syrup and carbonated water. Beverage dispensers of the ice bank variety use refrigeration equipment including a compressor, condenser and evaporator to form an ice bank around the evaporator coils. The ice bank is suspended in a tank of cold water and provides a cooling reserve for the carbonated water and syrup beverage constituents.




A major problem with the ice banks concerns the regulation of the size thereof. Mechanical and electro-mechanical controls are known, however such controls can be slow to respond and therefore result in wider than desired fluctuation in the size of the ice bank. Electronic controls are known whereby a pair of probes determine the presence of ice or water as a function of the conductivity thereof However, early electronic controls suffered from reliability problems, and the probes over time can become corroded and therefore provide unreliable information. Furthermore, both mechanical and electronic controls have the problem of hysteresis management wherein undesirable short cycling of the refrigeration compressor can occur. Such prior art controls have not been able to determine with a high degree of certainty if ice is present, and if so is there is sufficient thickness that further ice production should be terminated.




A similar problem exists in current art beverage dispensers with respect to the carbonator. The carbonator, of course, is the vessel wherein plain water and carbon dioxide are combined to produce the carbonated water. Typically, a carbonator includes a probe positioned therein having high and low probe contact points for electronically determining the level of water within the carbonator. Specifically, the probes determine the presence of water or air with respect to the difference in electrical resistance there between. Prior art level controls of this type, as with ice bank controls, suffer with the problem of accuracy. The interior of the carbonator is a dynamic environment where water and carbon dioxide are being combined causing turbulation and spray: Thus, it has always been difficult to know if the water is in fact sufficiently low to require water to be pumped to the carbonator. Since it is difficult to know the level of the water in the tank, it is also difficult to build in any form of hysteresis control so that the pump is not short cycled.




A further problem with prior art dispensers of the ice bank type concerns the control of the agitator motor. The agitator motor is used to circulate water within the water tank in which the ice bank resides to enhance heat exchange between the ice and the water and ultimately the beverage constituents. In such prior art dispensers agitator motors are generally operated continuously. However, such use of electrical power is wasteful, especially during periods of time wherein the dispenser is not in use. Thus, it would be desirable to operate the agitator motor more in accordance with the actual need thereof.




It is also known that the carbonator can become less effective at carbonating plain water over time. This can occur as a result of oxygen and other gases entrained in the water being released therefrom within in the carbonator. Eventually, the air space within the carbonator that is ideally totally carbon dioxide, can include a substantial percentage of oxygen, nitrogen, and so forth. Thus, various strategies have been proposed to use a solenoid operated valve to periodically vent air from the carbonator air space and replace it with carbon dioxide. However, such devices typically purge air from the carbonator based upon a predetermined time lapse. It would be more desirable to purge the carbonator based more directly upon the actual presence of contaminating gases as opposed to the lapse of a predetermined period of time where such purging may occur needlessly.




SUMMARY OF THE INVENTION




The present invention is an electronic control for use with a beverage dispenser, and particular a beverage dispenser of the ice bank type. Such a beverage dispenser includes a water tank for holding a volume of water. The water is refrigerated by an evaporator suspended therein and connected to a compressor and a condenser. A fan motor is used to cool the condenser. A plurality of syrup lines extend through the tank for cooling thereof and are connected to a plurality of beverage dispensing valves secured to the beverage dispenser. In the preferred embodiment, a carbonator is positioned within the water tank to provide for direct cooling thereof. The carbonator includes a level sensor having low and high sensing contact points and includes a solenoid operated safety valve. The carbonator has a plurality of carbonated water lines extending therefrom for connection to the plurality of beverage dispensing valves. An agitator motor is secured to the dispenser and includes a shaft and an agitating plate for providing movement of the water in the water bath. An ice bank sensor is positioned within the water bath with respect to the evaporator coils to provide for the formation of the desired sized ice bank on the evaporator coils. The ice bank sensor includes two probes across which an electrical pulse can be generated. A temperature sensing probe is positioned with respect to the evaporator coils so that it exists centrally within the ice bank. A water pump provides for pressurized delivery of plain water to the carbonator tank.




The electronic control of the present invention includes a microprocessor connected to and receiving information from the ice bank sensor, the temperature sensor and the carbonator level sensor. In turn, the microprocessor is connected to and provides for the control, of the solenoid safety valve, the agitator motor, the water pump and the compressor. Of course, the ice bank sensor, the temperature sensor, the carbonator level sensor, the solenoid safety valve, the agitator motor, the water pump and the compressor all have specific circuitry associated therewith through which the microprocessor exercises control and receives information. Power is supplied to the microprocessor by a regulated supply and further input is provided thereto by a zero crossing circuit. A constant reference voltage circuit is supplied to the microprocessor and to the ice bank probe and carbonator probe.




The microprocessor is programmed to control the ice bank sensor and related circuitry wherein a DC signal is alternately permitted to flow in opposite directions between the two probes thereof.




The microprocessor is programmed to control the ice bank sensor and related circuitry wherein the presence or not of ice is determined by the change in resistance to electrical flow between the probes thereof. However, unlike the prior art a DC signal is alternately permitted to flow in opposite directions between the two probes thereof. Moreover, this energizing of the probes only occurs when readings are to be taken, otherwise there is no potential there between. Furthermore, it was found that if each sampling occurs for a period of time of less than 4 milliseconds, corrosive deposition from one probe to the other can be avoided. Also, the alternating of the direction of the current flow further serves to negate any deposition that could occur over time as well as permit the use of DC current which allows for simpler and less costly circuitry than with the use of AC current as seen in the prior art. The sampling is controlled by software wherein 8 readings are taken after which the two highest and two lowest readings are thrown out and the remaining four are averaged. The resulting reading is compared to high and low set points that have been experimentally determined based upon the known range of water qualities as well as the particular dimensions of the ice sensor, its specific performance in water of varying ionic and particulate content and so forth. Thus, the compressor will be signaled to turn on to build the ice bank if the sensed resistance is below the low set point, and conversely will be turned off if the averaged reading is above the high set point. No change in the current state, whether it be make ice or not make ice, will occur if the averaged reading is between the low and high set points. The high and low set points therefore provide for hysteresis management so that the determination of the existence of ice or not over the probes can be done with a high degree of reliability. In addition, a reading of the temperature probe is also taken simultaneously with the determination of the resistance between the ice bank probes. If the determination is that ice is present over the probes, an increment, in the present case 0.9degrees F. as experimentally determined, is subtracted from the current ice bank temperature reading. Rather than immediately turning off the compressor, it is left running until the ice bank temperature probe reads this lower temperature. As is understood by those of skill, to increase the size of an ice bank requires the refrigeration system to work progressively harder. Thus, there is a correlation between the temperature within the ice bank and its overall size or thickness. Therefore, by permitting the compressor to run based upon the temperature of the ice bank, a further desired amount of ice can be safely and accurately added to the ice bank beyond the physical position of the probes. In addition, ambient load proportionally affects the amount of ice which is added to the ice bank. The product of the refrigeration system cooling rate and the ice thickness forms the basis for determining the amount of ice added. As the ambient load increases, the refrigeration cooling rate decreases, forming increased or additional ice reserve compared to nominal ambient loads. The increased ice reserve is beneficial to provide additional cooling reserve when needed in higher ambients. The reverse also hold true wherein lower than nominal ambients will produce less ice when additional cooling is not needed. It can be seen that such an approach further protects against undesirable short cycling of the compressor as is not turned off at the first indication of ice at the ice sensing probes, which particularly during a period of high volume beverage dispensing, could very quickly result in melting of that ice and a determination that ice should again be produced.




The carbonator probes also use a DC signal, but, unlike the ice bank sensor probes. since the current flow is not between the high and low water level probes but between each probe and the grounded carbonator tank, reversal of such flow is not necessary. However, in the carbonator level sensing circuit, like that of the ice bank sensing circuit, current is not present at the high and low probes unless readings are being taken. The microcontroller software then directs the sampling of each probe 64 times in time spans of less than 4milliseconds to prevent any corrosive degradation. The 64 samples provide for determining with high reliability that each probe is either in air or water. If they are both in air the water pump is turned on, if they are both in water the pump is turned off. If the high and low water level probes disagree, that is, one is in air and the other in water, then no change is made to the current pump operation.




The carbonator safety valve is operated periodically based upon an accumulation of pump run time. Thus, unwanted gases are released from the carbonator based upon a factor that relates directly to the presence of those unwanted gases therein.




The agitator motor is operated as a function of the temperature sensed by the temperature probe during initial start up of the dispenser when no ice is present on the evaporator coils. Also, the agitator is operated on the basis of whether or not the compressor and/or the carbonator pump have been running during a predetermined time period. Thus, if no drinks have been drawn during the predetermined time period, as indicated by no running of the water pump, or the compressor has not been running during that time period, also indicating no drink dispensing requiring ice bank replenishment, the agitator is turned off. Such agitator control was found to decrease the amount of time needed for and initial pull down forming a full ice bank, and to save energy by not running the agitator motor and not running the compressor to replace ice needlessly eroded by constant running of the agitator.











DESCRIPTION OF THE DRAWINGS




A further understanding of the structure, operation, and objects and advantages of the present invention can be had by referring to the following detailed description which refers to the following figures, wherein:





FIG. 1

shows a perspective view of a carbonator.





FIG. 2

shows a top plan view along lines


2





2


of FIG.


1


.





FIG. 3

shows a partial cross-sectional side plan view along lines


3





3


of FIG.


2


.





FIG. 4

shows an end plan view long lines


4





4


of FIG.


3


.





FIG. 5

shows a cross-sectional view along lines


5





5


of FIG.


3


.





FIG. 6

shows a side plan partial cross-sectional view of an ice bank cooled beverage dispenser.





FIG. 7

shows a top plan view along lines


7





7


of FIG.


6


.





FIG. 8

shows an enlarged exploded view of the ice bank probe, temperature probe and evaporator coil mounting plate.





FIG. 9

shows an enlarged front plan view of the ice bank probe secured to the evaporator coil mounting plate.





FIG. 10

shows a side plan view along lines


10





10


of FIG.


9


.





FIG. 11

shows an enlarged cross-sectional view of the solenoid operated safety valve.





FIG. 12

is an overall schematic diagram of the electronic control of the present invention.





FIG. 13

shows a schematic view of a plain water connection to a dispensing valve.





FIG. 14

is a schematic diagram of the ice bank probe control circuitry.





FIG. 15

is a schematic diagram of the carbonator probe control circuitry.





FIG. 16

is a schematic diagram of the solenoid operated safety valve and the temperature sensing control circuitry.





FIG. 17

is a schematic diagram of the agitator motor, the carbonator and the compressor control circuitry.





FIG. 18

is a schematic diagram of the boost pumping circuitry and of the microprocessor and connections thereto.





FIG. 19

is a schematic diagram of the power and zero crossing circuitry.





FIG. 20

is a schematic diagram of the voltage regulating and voltage reference circuitry.





FIG. 21

is a flow diagram of the microprocessor control of the ice bank probe and the data received therefrom.





FIG. 22

is a flow diagram of the microprocessor control of compressor.





FIG. 23

is a flow diagram of the microprocessor control of carbonator probe and the data received therefrom.





FIG. 24

is a flow diagram of the microprocessor control of plain water pump.





FIG. 25

is a flow diagram of the microprocessor control of agitator motor.





FIG. 26

is a flow diagram of the microprocessor control of solenoid operated carbonator safety valve.











DETAILED DESCRIPTION




A carbonator is seen in

FIGS. 1-5

and generally is referred to by the numeral


10


. As seen therein, carbonator


10


includes a first half


12


and a second half


14


. Halves


12


and


14


are made from a suitable sheet metal such as


18


gauge stainless steel. In particular, they are cold drawn to form an alternating pattern of seams


16


and ridges


18


. Halves


12


and


14


are welded together around their respective perimeter edges having top and bottom perimeter edge portions


20


and


21


respectively and side edge portions


22


, and along corresponding seams


16


, to form the carbonator tank


22


. It can be seen that tank


23


includes a top tank volume area


24


, a bottom area


26


and a plurality of vertical column areas


28


. The top and bottom areas


24


and


26


provide for fluid communication between the columns


28


. A top end


29


of tank includes a solenoid operated pressure relief valve


30


, a carbon dioxide inlet fitting


32


, a water inlet fitting


34


and a level sensor fitting


36


for retaining a water level sensor


38


. Sensor


38


includes a high level sensing contact


38




a


, and a low level sensing contact


38




b


that are connected by a pair of wires


40


to control means described in greater detail below. A J-tube


41


is secured to fitting


34


and extends within a column


28


.




A plurality of carbonated water lines


42


extend from a bottom end


43


of tank


23


and include vertical portions


42




a


that travel upwardly closely along and adjacent first half


12


and then extend with horizontal portions


42




b


over end


29


and outwardly therefrom in a direction towards side


14


and terminate with beverage valve fittings


44


.




As is seen by referring to

FIGS. 6 and 7

, carbonator


10


is shown in an ice bank type of beverage dispenser


50


. As is known in the art, dispenser


50


includes an insulated water bath tank


51


having a bottom surface


51




a


, a front surface


51




b


, and rear surface


51




c


and two side surfaces


51




d


. A plurality of evaporator coils


52


are held substantially centrally within tank


51


and substantially below a surface level W of water held in tank


51


for producing an ice bank


53


thereon. Carbonator


10


is located within tank


50


and adjacent a front end


54


of dispenser


50


. In particular, dispenser


50


includes a plurality of beverage dispensing valves


55


secured to the front end


54


. It can be understood that carbonated water fittings


44


allow lines


42


to be hard-plumbed directly to each valve


55


. A transformer marked TR is connected to an AC line voltage supply and provides 24VAC current to the valves


55


. Dispenser


50


also includes a removable plate


56


that provides access to a space


57


between plate and tank


50


. A water delivery line


58


is connected to a source of potable water and routed through space


57


to a water pump


59


. Pump


59


pumps water through a line


60


to carbonator


10


. The majority of the length of line


60


consists of a serpentine coil


60




a


submerged in tank


50


to provide for cooling of the water flowing there through. Coil


60




a


is arranged in four convoluted or serpentine portions centrally of evaporator coils


53


. Evaporator coils


53


are, as is known in the art, connected to a refrigeration system. Specifically, the refrigeration system main components include, a refrigeration compressor


61


secured to a top deck floor


62


, a condenser


63


held by a support and air directing shroud


64


above a cooling fan


64




a


operated by a motor


64




b


.An agitator motor


65


includes a shaft


65




a


and a turbulator blade


65




b


on an end thereof, and is secured at an angle to floor


62


by an angled support


65




c


. A carbon dioxide gas delivery line


66


is routed through space


57


and is connected to gas inlet


32


. Each valve


55


is connected to a syrup line


67


. Lines


67


are each connected to a source of syrup and are also initially routed through space


57


and then consist of a plurality of loops positioned closely adjacent carbonator


10


in tank


51


. Lines


67


then terminate by direct hard plumbing to valves


55


as the ends thereof come up and over carbonator top end


29


. Tank


51


includes a front ridge


68


, and a U-shaped ridge


69


, integrally molded into bottom surface


51




a


thereof. Ridge


68


includes an angled surface


68




a


, and extends across the width of tank


51


from one side


51




d


to the other. Ridge


69


has two parallel components


69




a


extending in a direction from dispenser front end


56


to the rear end opposite therefrom, and a component


69




b


perpendicular thereto and extending there between forming the “U” shape. Ridge portion


69




a


and


69




b


each include a portion


69




c


that extends transversely to tank bottom


51




a.






As seen in

FIG. 8

, an ice bank sensor


70


and a temperature sensor


72


are secured to a retaining bracket


74


which in turn is releasably securable to evaporator coils


52


. As seen by also referring to

FIGS. 8

,


9


and


10


, bracket


74


includes a pair of lower coil retaining arms


76


and a flexible coil engaging tab


78


. Bracket


74


also includes a temperature probe guide arm


80


having a guide hole


81


therein, and three ice bank sensor retaining holes


82


extending through a flat vertical surface


83


thereof. Hole


81


provides for slideably receiving the body


84


of temperature sensor


72


. Sensor


72


also includes an upper plate


86


for securing to deck


62


and includes a pair of wires


88


for connection to a control means. Ice bank sensor


70


includes a sensor retaining clip


90


having a wire retaining portion


92




a


and a protective portion


92




b


. Protective portion


92




b


is secured to retaining portion


92




a


by a live hinge


94


. Retaining portion


92




a


includes elevated end portions


96




a


and


96




b


. Portion


96




a


includes a wire retaining recessed area


98


and return receiving cavities


99


, and portion


96




b


includes a pair of probe end retaining holes


100


. Portion


92




a


also includes three legs


102


for providing snap fitting retaining thereof with bracket holes


82


. Portion


92




b


includes two flexible clip arms


104


having returns


104




a


thereon and a pair of probe protectors


105


. Dual wires W, as seen in

FIGS. 8 and 9

, are partially separated and have some insulation removed therefrom thereby creating probes


106


and


108


. Each probe


106


and


108


include bent ends


106




a


and


108




a


respectively for inserting into probe holes


100


. It can be understood that wires W are retained within clip


90


wherein after insertion of probe ends


106




a


and


108




a


into holes


100


, and an insulated portion of wires W is placed within recessed area


98


, portion


92




b


can be secured to portion


92




a


. Specifically, as seen in

FIG. 10

, clip arms


104


provide for snap fitting securing where returns


104




a


of clip arms


104


provide for snap fitting securing to end portion


96




a


wherein the return retaining slots


99


thereof hold returns


104




a


. Clip


90


can then be secured to bracket


74


by insertion of the legs thereof into holes


82


. Bracket


74


is secured to evaporator coils


52


by first receiving an individual coil


52


in arms


76


and then snap fitting flexible tab


78


over a further coil


52


. Temperature sensor


72


is secured to dispenser


50


wherein probe body


84


is guided through hole


81


thereof and plate


86


is secured to deck


62


. Protectors


105


serve to prevent physical disruption or contact with probes


106


and


108


.




As seen in

FIG. 11

, solenoid valve


30


includes a solenoid


110


and operating arm


112


. Arm


112


is connected to a valve arm


114


which includes a valve end


114




a


. Valve end


114




a


provides for sealable seating with seat


116


. Valve arm


114


is secured to solenoid arm


112


by a pin


118


. A spring


120


extends around arm


114


and provides for biasing seat end


114




a


against seat


116


. Valve arm


114


and spring


120


are retained within a lower valve housing portion


122


. Housing portion


122


includes a lower hole


124


and a plurality of perimeter holes


126


. Arm


112


is also secured to a manual actuating ring


128


. Solenoid


110


includes electrical contacts


130


for connection by wires


132


to control means and power circuitry therefore.




As seen in

FIG. 12

, the present invention includes a microcontroller


140


for providing electronic control of the safety valve


30


, ice bank temperature sensor


72


, carbonator probe


38


, ice bank sensor


70


, agitator motor


65


, pump


59


, and compressor


61


. Valve


30


, ice bank temperature sensor


72


, carbonator probe


38


, ice bank probe


72


, agitator motor


65


, water pump


59


, and compressor


61


each include particular control circuits


142


,


144


,


146


,


148


,


150


,


152


, and


154


respectively associated therewith. Power is supplied to the present invention by power supply circuit


156


having a +5volt Vcc circuit


157


and a zero crossing circuit


158


. The control of the present invention also includes a boost pump circuit


160


and reference and threshold voltage circuits


162


and


164


.





FIG. 13

shows a schematic diagram of the situation where a beverage valve


55


is connected to a plain water line L coming off a T-fitting marked T. Plain water is supplied to line L by pump


59


. Line


60


provides water to carbonator


10


, and as is known in the art, a check valve CV is used to prevent carbonated water from exiting back from carbonator


10


into line


60


. If the plain water supply is of a low pressure, such as below 30 PSI, pump


59


is turned on by circuit


160


as controlled by microcontroller


140


to provide additional pressure. Transformer TR provides the 24VAC to each solenoid


55




a


of each valve


55


. The 24 VAC is provided to connector J


5


of boost circuit


160


, seen in

FIG. 18

, and as described in further detail below, for operating pump


59


. This connection is made at installation of dispenser


50


if the water supply pressure is low. Thus, pump


59


will be operated when a beverage valve


55


using plain water is activated. The water will then flow to that valve


55


. Check valve CV along with the pressure in carbonator


10


will prevent the plain water from flowing therein.




A detailed view of the control circuitry


148


for ice bank sensor


70


is seen by referring to FIG.


14


. Circuit


144


includes a line


166


for providing a known reference voltage to a pair of pull-up resistors R


11


and R


13


. Probe wires


106


and


108


are connected by wires W to resistors R


11


and R


13


respectively. A pair of open collector inverting buffers U


1


A and U


1


B are connected via lines


168


and


170


to probes


106


and


108


and resistors R


11


and R


13


respectively. Lines


168


and


170


in turn provide for connection to a logic ground as represented by microprocessor pins PC


4


and PC


5


, as seen in

FIG. 18. A

pair of non inverting unity gain op-amps U


2


B and U


2


A are connected by lines


172


and


174


to probes


106


and


108


respectively. Each op-amp U


2


A and U


2


B include input protection as provided by resistors R


1


and R


2


diode D


3


and D


1


and capacitors C


7


and C


6


respectively. Op-amps U


2


A and U


2


B are, in turn, connected to microprocessor


140


along lines


176


and


178


.




The operation of circuit


148


can be understood wherein a current coming in along line


166


will normally flow to resistors R


11


and R


13


to a logic ground through buffers U


1


A and U


1


B. When a reading of the conductivity of the water existing between probes


106


and


108


is desired for determining whether or not water or ice is present, electrically current is induced to flow between probe wires


106


and


108


by, for example, the signaling of buffer U


1


A to switch from ground to an open circuit. Thus, the current will flow through resistor R


11


to probe


106


and after a period of time a voltage and current flow equilibrium will reached wherein current will now flow from probe


106


to probe


108


and to logic ground represented by buffer U


1


B. As this current flow is DC, the direction of current flow between probe wires


106


and


108


is periodically reversed so as to minimize any corrosive effects as a result of the DC current. The specific-manner of reversing of such current flow and the sensing thereof by Microntroller


140


will be described in greater detail herein below. Thus, it will be apparent to those of skill, that such a reversal of flow will occur wherein buffer U


1


B is switched from ground to an open state and conversely buffer U


1


A is switched from an open state to ground. Thus, current will flow along resistor R


13


in the direction from probe


108


to probe


106


. It can also be understood that when current is flowing in the direction from probe


106


to


108


op-amp U


2


B will be able to detect the magnitude of such and report such analog information to microcontroller


140


. Microcontroller


140


includes an analog to digital converter which converts the signal from op-amp U


2


B to a scale of zero to 255 wherein zero represents 0V and 255 represents 2.5V. In the same manner, op-amp U


2


A provides an analog signal proportional to the magnitude of current flow in the direction of probe


108


to probe


106


. As stated, an advantage of the present ice bank detecting circuit of the present invention concerns the ability to reverse the direction of flow to minimize any corrosion of either of the probes. Moreover, it can be seen that there is no potential at the probes other than when readings are to be taken, and such readings within a two millisecond window to further prevent any corrosive deposits. It was found that a 4 millisecond threshold current flow time must occur before any corrosive deposition occurs. Thus, keeping such reading time below that threshold will serve to prevent any corrosive deposition on either of the probes.




The carbonator probe circuitry


146


is seen in greater detail in FIG.


15


. Lines


180


provide reference voltage to resistors R


9


and R


10


. A high level water level sensor probe


38




a


is connected via line


182


to resistor R


9


and a lower water level sensor probe


38




b


is connected via line


184


to resistor R


10


. Open collector inverting buffers U


1


E and U


1


F are connected by lines


186


and


188


to lines


184


and


182


respectively. Buffers U


1


E and U


1


F are connected to a logic ground via line


190


. A comparator U


6




a


is connected to line


182


and to a threshold voltage along line


192


. Similarly, a second comparator U


6




b


is connected to line


184


and connected to the same threshold voltage via line


194


. Both comparators U


6




a


and U


6




b


include resistors R


5


and R


4


, diodes D


2


and D


4


, and capacitors C


8


and C


9


respectively for providing input protection as is understood by those of skill. Comparators U


6




a


and U


6




b


have outputs connected to microcontroller inputs A


5


and carbonator level sensor also includes a contact


196


connected by jumper


197


to a ground


198


through the carbonator tank


23


which is connected to ground. As an integral part of the level sensor, when the sensor connector is removed from the control, the contact


196


is connected by line


199


to VCC which can be detected by the microcontroller


140


. This will prevent the pump operation when no carbonator level sensor is connected to the control.




The operation of the carbonator probe level sensing circuitry is similar to that of ice bank control circuitry


144


. In particular, buffers U


1


E and U


1


F are generally held at logic ground wherein current flows along lines


180


through resistors R


9


and R


10


through buffers U


1


E and U


1


F of line


190


. If a reading of upper level probe


38




a


is to occur, buffer U


1


F is changed to an open state wherein current will now flow from upper probe


38




a


to the grounded carbonator tank


23


. Similarly, if a reading of lower probe


38




b


is to take place, buffer U


1


B is signaled to change to an open state wherein potential will now form between


38




b


and the grounded tank


23


. As with prior art carbonator level sensing probe, sensing of air or water is determined by the difference in resistance to flow there between. However, unlike the situation just described for sensing the presence of water or ice where such differences are proportionately smaller and more subject to variability with respect to purity, or lack thereof, in the water forming the ice bank, the difference in resistance of flow between water and air is quite dramatic. Thus, comparators U


6




a


and U


6




b


can be used to send a digital signal to microcontroller


140


wherein a high reading will indicate a presence of air and a low reading will indicate the presence of water. Thus, comparators U


6




a


and U


6




b


only need a threshold of voltage supplied thereto along lines


192


and


194


to which to compare the signals from probes


38




a


and


38




b


. Microcontroller


140


will therefore signal the operation of pump


59


based upon the inputs from circuit


144


. A more detailed understanding of the air level probe control logic will be discussed herein below.




Referring to

FIG. 18

, single chip microcontroller


140


is seen. In the present invention, controller


140


is a model MC68HC05 made by Motorola having a microprocessor, RAM, an onboard A to D converter and the particular programming of the present invention contained in the permanent memory thereof Crystal X


1


, capacitors C


10


and C


11


, and resistor R


13


form the clock oscillator for microcontroller


140


, and capacitor C


20


provides power input filtering therefor. The output port pins of microcontroller output directly control the AC outputs to compressor


61


, carbonator water pump


59


, and agitator motor


65


. The low voltage outputs thereof control ice bank sensor


70


, carbonator level sensor


38


and their associated circuitry


148


and


146


. Two status LEDs (D


15


and D


16


) are directly under software control.




As also seen in

FIG. 18

, resistor R


30


, diode D


7


and the opto-coupled darlington transistor (ISOl) form a carbonator pump boosting input to the microcontroller. A 24V AC signal applied to pin


3


of J


5


will activate pump


59


.




As seen in

FIGS. 18 and 19

, 24V AC input power is supplied to connector J


5


pins


1


and


2


. Diode D


12


, capacitors C


19


and C


21


, voltage regulator U


4


and resistors R


36


and R


38


form a half wave rectified +12V DC power supply. The +12V DC supply has dual use as a pre-regulator for +5V DC “VCC” power supply


158


and the power for the a relay coil T


90


seen in FIG.


16


. The pre-regulator is necessary to provide reliable operation over a wide input voltage range. Resistor R


34


and zener diode D


14


are provided for operation at the high limit of input voltages. Diode D


13


and capacitor C


18


are included as noise filter elements to protect the power regulators from transient voltages developed when switching the compressor relay coil K


1


. The metal oxide varistor RV


1


is included to protect the circuit board from power line transient voltages. Resistor R


37


and capacitor C


22


provide some additional power dissipation for the +


5


V DC regulator (US) to allow operation without a heat sink.




As seen in

FIG. 19

, a zero-cross circuit


158


consisting of R


31


, C


12


, D


6


, R


32


, R


33


and transistor Q


3


provides pulse outputs to an input port pin of microcontroller


140


to indicate when the input AC power is near zero volts. This signal is used to synchronize a compressor relay T


90


with the input power to minimnize current surges at turn-on and electrical noise spikes at turn-off of the compressor.




As seen in

FIG. 20

, circuit


157


includes regulator


1


C (U


5


) for providing a +5V DC output from the pre-regulated +


12


V DC input. Capacitors C


15


, C


4


and C


1


provide electrical noise filtering for reliable operation of the control. Regulator U


5


also monitors the +5V DC power through “sense” input and provides a logical reset signal to microcontroller


140


when power is below the safe operating limit. Capacitor C


23


provides additional reset pulse filtering to microcontroller


140


.




The ice bank temperature, ice bank continuity and carbonator level detect circuits


144


,


148


and


146


require a stable voltage reference to measure their respective parameters. As seen in

FIG. 20

, circuit


162


includes resistive divider R


35


and R


14


with capacitor C


3


to divide the +5V DC in half to +


2


.5V DC. An operational amplifier (U


2


C) buffers the +


2


.5V signal with a low-impedance driver to isolate the off-board components from the on-board components to minimize electrical noise interference on the control board.




The carbonator circuit comparators U


6


A and U


6


B need a voltage threshold to compare against the input signals to make a logic level decision whether the probes are in air or “water”. Resistors Rl


6


and Rl


7


divide the +5V DC “VCC” to provide the threshold signal. Since the signal does not leave the circuit board, no additional buffering with an op-amp is needed.




As seen in

FIG. 16

, the ice bank temperature thermistor sensor circuit


144


forms a voltage divider circuit with resistor R


7


and filter capacitor C


2


. The operational amplifier U


2


D provides all the signal conditioning needed to expand the sensor usable signal range to cover the expected ice bank temperature range. Resistors R


3


, R


6


and R


8


provide the needed gain and offset.




As seen in

FIG. 17

with respect to agitator control circuit


150


, microcontroller output port pin controls the LED half of an optically coupled triac driver IS


04


. In addition, when the agitator output is active, LED D


10


will also be illuminated. The output power for agitator motor


65


is directly switched through triac Q


4


. Resistors R


20


, R


21


and capacitor C


14


form a “snubber” circuit to provide reliable “switching” operation.




As seen in

FIG. 17

with respect to carbonator pump circuit


152


, a microcontroller output port pin controls the LED half of an optically coupled triac driver IS


03


. In addition, when the carbonator output is active, LED D


9


will also be illurminated. The output power for carbonator motor


59


is directly switched through a heavy duty triac Q


1


, which is attached to a heat sink to dissipate heat when pump


59


is running. Resistors R


18


, R


19


and capacitor C


17


form a “snubber” circuit to provide reliable “switching” operation. Fuse F


1


is included in the output to protect the circuit components if pump motor


59


becomes stalled, since motor


59


has no internal overcurrent protection.




As seen in

FIG. 17

with respect to compressor control circuit


154


, a microcontroller output port pin controls a transistor switch formed by Q


2


and resistors R


39


and R


40


. In addition, when the compressor output is active, LED D


8


will also be illuminated, Diode D


5


protects the transistor switch from electrical transients which occur when the relay is switched off. The output power for compressor


61


is directly switched through the relay contacts. Resistor R


12


and capacitor C


13


form a “snubber” circuit to provide long reliable contact life while reducing electrical noise interference.




As seen by referring to

FIG. 16

with respect to safety valve control circuit


142


, a microcontroller output port pin controls the LED half of an optically coupled triac driver IS


02


. In addition, when the safety valve output is active, LED D


11


will also be illuminated. The output power for valve


30


is directly switched through triac Q


5


. Resistors R


22


, R


23


and capacitor C


16


form a “snubber” circuit to provide reliable “switching” operation.




An understanding of the operation of the present invention can be had by referring to the flow diagrams contained in

FIGS. 21 through 26

. It will be understood, by those of skill, that microcontroller


140


includes specific programming for operating the various components of a beverage dispenser. Such flow diagrams being illustrative of the control of such components as exercised by microcontroller


140


as a function of its specific programming.




A more detailed understanding of the operation of ice sensor


70


and related circuit


148


can be had by referring to FIG.


21


. As seen therein, current is made to flow from probe


106


to


108


by energizing of buffer U


1


A. Four individual readings are taken wherein buffer U


1


B is switched between an open state and logic ground four times with a suitable wait period there between to provide for the voltage and current flow to stabilize. At block


204


buffer U


1


A is switched to logic ground after which buffer U


1


B at block


206


is switched to an open state. Block


208


four readings are taken by op-amp U


2


A current flow from probe


108


to


106


as a result of the cycling between an open state and logic ground by buffer U


1


B. At block


210


both buffers U


1


A and U


1


B are held to a logic ground. At block


212


there now exists eight individual conductivity readings wherein the highest two and lowest two such readings are thrown out and the remaining four readings are averaged. Decision block


214


the microcontroller determines whether or not a make ice mode is set. Thus, if microcontroller


140


has previously determined that ice should be made, the make ice mode will have been set as will become more clear in the following flow diagram. If the make ice mode is not set, then at decision block


216


it is determined as calculated by block


212


, is below a low set point. The low set point is a resistance level that has been chosen therein if the resistance determined by sensor


90


is below this level then water is indicated and a change to a make ice state occurs at block


218


then LED


1


is turned on at block


220


. If however, at decision block


216


the average is greater than the low set point, no change in state is indicated and this routine is exited. If at decision block


214


the make ice mode is set, then at decision block


222


it is determined if the average resistance value calculated at block


212


is greater than a high set point. The high set point is a resistance level selected as being indicative of ice being present covering probes


106


and


108


. If the average calculated at block


212


is greater than the high set point, then the microprocessor changes to a stop make ice state after which LED


1


is turned off at block


226


. If at decision block


222


the average determined at block


212


is less than the high set point, then no change in the ice mode is made and the routine is exited.




The programmed control of compressor


61


can be understood by referring to FIG.


22


. As seen therein at block


228


it is first determined whether or not compressor


61


is running. If the answer is yes, at decision block


230


it is determined whether or not the program is in the make ice mode. If the compressor and it is the make ice mode then a stop flag is cleared at block


232


after which at block


234


the ice bank temperature probe


70


is read and at decision block


236


it is determined if the temperature is below a fail safe level. This fail safe temperature is experimentally determined as a temperature indicating that the ice bank, for whatever reason, has grown too large, thereby indicating some sort of mechanical and/or electronic failure. Thus, at block


238


the compressor is shut down, failure is indicated. The compressor startup is locked out wherein the compressor can only be restarted by a manual reset. If at decision block


230


the routine is not in the make ice mode at decision block


240


the decision is made whether or not the stop flag is set. If it has not been set at block


240


it is set and the routine flows through to return. On a subsequent time through at decision block


240


the decision will be that the stop flag is set. The reason for the stop flag is that the sensing of the presence of ice by ice bank sensor


90


and as per the flow diagram of FIG.


21


and the running of the present compressor control regime occur every 30 seconds. Thus, requiring stop flags ensures that at least two measurements are taken 30 seconds apart with respect to the decision of whether to turn off compressor


61


. This approach provides for added assurance that ice bank probes


106


and


108


indeed are covered with ice as opposed to a transient situation. Continuing, at decision block


244


routine asks is this the first time through. In the present case. since this will be the first time through and at decision block


246


ice bank temperature probe


72


is read and 0.9° F. is subtracted from that currently sensed temperature and stored as a set point. The next time through, assuming the compressor is running, make ice mode is yes, stop flag is set at decision block


246


, this will now be the second time through, for purposes of this discussion, after which at block


248


the current temperature is read and compared with the previous stored set point. If at decision block


250


the read temperature is greater than the set point then the compressor is left running and again cycles through blocks


234


,


236


, and


238


. If the sensed temperature is less than the set point then at block


252


turn off the compressor and clear a two minute timer. The reason for the “first time” question block


246


is to provide a set temperature point for determining when the compressor should be turned off. It was experimentally determined that the 0.9° F. increment that must be reached at decision block


250


before compressor


61


can be turned off. Thus, compressor


61


is not turned off immediately when ice is determined to be covering probes


106


and


108


, but is allowed to run and develop additional ice beyond probes


106


and


108


. In the particular embodiment described herein, the 0.9° F. was found to provide for the desired additional amount of ice bank deposition. It can be appreciated by those with skill that decision block


246


permits a fixing of that ice temperature set point so that the routine can subsequently flow to block


248


. Otherwise, the set point would be changed each time and the compressor would not turn off. If at block


228


it is determined that the compressor is not running, at decision block


253


it is first determined if the compressor is in lock up. If it is the routine goes to return and compressor can not be started. If it is not in lock up, at decision block


254


it is determined whether or not the two minute timer has expired. If not, the routine flows to the return and repeats. If subsequently it is determined that the two minute timer had expired then at decision block


256


it is determined whether or not we are in the make ice mode. If it is not in the make ice mode at block


258


a start flag is cleared. If at block


256


it is the make ice mode, then at decision block


260


it is determined if this is the second time through. If it is not, the start flag is set; if it is, the compressor is turned on at block


262


the start flag is set. An understanding of the foregoing wherein at block


254


a two minute timer must expire from the last time compressor


61


was turned off before it can be turned on. This, of course, provides for a short cycling protection. Moreover, compressor


61


is not turned on at block


264


until at block


260


it is determined that this is the second time through the routine. Thus, at least two determinations 30 seconds apart must confirm that probes


106


and


108


are sensing water.




The control of the carbonator probes can be understood by referring to FIG.


23


. At block


270


high and low probe


38




a


and


38




b


are turned on and the logical signal is sent along line


192


to buffers U


1


E and U


1


F. Though both probes are turned on simultaneously, unlike the situation with ice bank probes


106


and


108


, there is not need to reverse current flow that would result in flow from carbonator tank


23


to the probes. However, as with probes


106


and


108


each probe


38




a


and


38




b


is read individually although there will be a potential at both. Thus, at block


272


after a suitable delay period at block


274


probe


38




a


is read


64


times during a total on time of less than 4 milliseconds and generally approximately 2 milliseconds. The signal along line


192


then provides for turning off buffers U


1


E and U


1


F at block


276


. The probes are then turned on again at block


278


after a suitable delay time to allow the voltages to stabilize at block


280


probe


38




b


is read


64


times, again within the same time frame as the readings occurring at probe


38




a


. At block


284


the probes are again turned off. At block


286


the


64


samples of probe


38




a


are read and it a majority indicate the probe is in air then that status is set at block


288


. Or if the majority of readings indicate that the probe is in water, that particular set is set at block


288


. At block


290


the same procedure occurs for the readings taken with respect to sensor


38


b. Then at block


292


if the majority of readings indicate air or water, that particular status is set. It will be apparent to those with skill that the readings of the carbonator level probes will be received by microcontroller


140


as digital information rather than the analog information provided by ice bank probes circuit


148


. So, at blocks


288


and


292


the probe status will remain the same as it previously was if the number of readings for water or air at any one probe are equal.




An understanding of the control of water pump


59


as a function of the determination of the water level sensor


38


it can be had by referring to FIG.


24


. At decision block


300


it is first determined if the plain water boost is active. As previously described the plain water boost is activated if incoming plain water pressure is not sufficient for providing flow of plain water to one of the valves. Thus, we are not concerned at this point whether or not the carbonator needs water as pump


59


is being operated to provide plain water to one of the valves. At decision block


302


we must first determine if pump


59


is in a lockup mode. If it is not, at block


304


we turn on pump


59


. At decision block


306


we determine if the maximum run time of pump


59


has been exceeded. If it has we indicate failure at block


308


, shut off pump


59


at block


310


and lockup the operation of pump


59


at block


3




12


so that restarting must require service personnel. If at decision block


306


the maximum run time has not been exceed then we can go to return. It can be appreciated by those with skill that decision block


306


provides a safety measure wherein if pump


59


has been running for a continuous period of time, for example, more than five minutes the failure is indicated such as a ruptured line for which the operation pump


59


should be terminated. If at decision block


300


plain water boost is not active, then the set values for probes


38




a


and


38




b


are reviewed. If at block


314


both probes are determined to be in air, then the pump will be turned on provided it is not in lockup. If at block


316


it is determined that both probes are in water and block


318


pump


59


is turned off and the maximum run time timer is reset at block


320


. If at decision block


322


, which we have reached because probes


38




a


and


38




b


do not agree, that is they are not both in water or both in air, it is determined if the pump is on. If it is it is allowed to run unless at block


306


the actual run time is exceeded. If the pump is not on, it is left off. Thus, if probes


38




a


and


38




b


are indicating the opposite condition, either air or water, from the other, then the current state is not changed and the pump is allowed to either run or not run depending on that current state.




Appreciation of agitator motor


65


can be understood by referring to the diagram of FIG.


25


. At decision block


330


it is determined if compressor


61


is on. If it is on at decision block


332


it is determined by temperature probe


72


if the ice bank temperature is above 65°. If it is, agitator


65


is turned off at block


324


. If the ice bank temperature is below 65° at decision block


326


it is determined if the ice bank temperature is below 60° F. If the temperature is between


65


° and 60° F., no change is made to the current operation of the agitator, whether it be on or off. If, however, temperature at block


326


is determined to be below 60° F., then agitator


65


is turned on at block


328


. Blocks


322


through


328


provide for control of agitator


65


at initial pull down, that is startup of dispenser


50


wherein no ice bank has of yet formed. Typically, in an initial pull down situation a compressor would run until it trips off because of the great cooling demand. This demand of course was exacerbated by the fact that, to quote prior art, dispenser the agitator motor would be running continuously. It was found that if the agitator motor were turned off in situations where the temperature was sensed to be above 65° compressor


61


would not have to run as much and would not run until it would trip off as a result of a safety in the compressor motor itself Thus, agitator


65


would only be run if the temperature reached a lower value such as 60° F. Of course, the 5° range between 60° and 65° provides for a hysteresis of management. It was found that this strategy provides for initial pull down to a full formation of a desirable ice bank in a shorter period of time than if the agitator motor were allowed to run constantly. If at block


330


the compressor is found to be off at decision block


340


is determined whether or not a carbonator


10


is located within the ice bank. If it is not, the agitto istred on and left running. Thus, in a non-integral carbonator situation, that is a remote carbonator, the agitator motor run continuously. If, however, the carbonator is located within the ice bank then at decision block


342


it is determined if water pump


59


and compressor


61


have both been off for a period of time greater than ten minutes. If both have been off for a period of time greater than ten minutes, then at block


344


agitator motor


65


is turned off. If, however, both pump


59


and compressor


61


had been not been off for a period of time greater than ten minutes then agitator motor


65


is turned on. In this manner, it can be appreciated that agitator motor


65


is only run in situations where pump


59


and/or compressor


61


had been running. In other words, the operation of agitator


65


is correlated to the drawing of drinks and/or the building of ice banks which is directly indicative of dispensing of drinks. Where in both situations cooling of beverage constituents is required. However, if pump


59


and/or compressor


61


had not been active for a period greater than ten minutes, this indicates that no drinks are being drawn and the operation of agitator


65


is unneeded. This is especially true of long periods of non-use such as overnight, where continuous operation of agitator


65


would result in erosion of the ice bank which would have to be replaced by operation of the compressor. Thus, not only is some energy saved by not running the agitator, a significant amount of energy is saved by not having to run the compressor to replace needless erosion caused by the agitator during periods of non-use.




The control of safety valve


30


can be understood by the flow,diagram seen in FIG.


26


. At decision block


350


it is determined if water pump


59


is running. If it is, that total run time is accumulated at block


352


. If the pump is not running at decision


354


it is determined if the pump run time accumulated at block


352


has exceeded a predetermined set point. If it has not, the pump is allowed to continue running. If it has, then the accumulation of run time is reset at decision block


356


and the solenoid of safety valve


30


is operated to release gases from carbonator


10


. In particular, valve


30


is pulsed rapidly rather than held open so that the gases in carbonator


10


are allowed to be released in small amounts. In this manner, the release of such gas does not cause undesirable noise.



Claims
  • 1. A device for regulating the size of an ice bank in a beverage dispenser, the dispenser having a tank for holding a volume of water and an evaporator coil, the evaporator coil connected to refrigeration system for providing cooling thereof for forming the ice bank thereon, the device comprising:an electronic control, a pair of probes, the probes held at a predetermined position relative to the evaporator coil, the probes connected to the electronic control and the electronic control providing for a flow of electrical current between the probes and the electronic control including a sensor for determining the magnitude of the resistance to the flow of the electrical current between the probes whereby the electronic control provides for determining the presence of ice at the predetermined position as a function of the magnitude of said resistance to flow, and the electronic control providing for no electrical potential between the probes except when periodically directing the electrical flow there between, and the electronic control alternating the direction of the flow of a DC electrical current between the probes.
  • 2. The device as defined in claim 1, and the electronic control having predetermined high and low resistance set points wherein the refrigeration system is operated if the sensed resistance is below the low resistance set point and wherein the refrigeration system is not operated if the sensed resistance is above the predetermined high resistance set point and wherein the operation of the refrigeration system is not changed if the sensed resistance is between the high and low resistance set points.
  • 3. The device as defined in claim 2, and the electronic control determining the resistance between the probes by sampling the resistance there between a plurality of times and throwing out a predetermined number of the high and low samples and averaging the remaining samples for determining the sensed resistance.
  • 4. The control device as defined in claim 3, and the predetermined probe position providing for holding the probes so that when the ice bank forms on the evaporator coil the probes are located within the ice bank and adjacent an outer surface portion thereof, and the control not starting operation of the refrigeration system unless a predated period of time has elapsed since the refrigeration system was last shut off.
  • 5. The control device as defined in claim 4, and the control means stopping the operation of the refrigeration means if the temperature sensed by the temperature sensing means at the second predetermined position goes below a predetermined low temperature value.
  • 6. A device for regulating the size of an ice bank in a beverage dispenser, the dispenser having a tank for holding a volume of water and an evaporator coil, the evaporator coil connected to refrigeration system for providing cooling thereof for forming the ice bank thereon, the device comprising:an electronic control, a pair of probes, the probes held at a predetermined position relative to the evaporator coil, the probes connected to the electronic control and the electronic control providing for a flow of DC electrical current between the probes and the electronic control including a sensor for determining the magnitude of the resistance to the flow of the DC electrical current between the probes whereby the electronic control provides for determining the presence of ice at the predetermined position as a function of the magnitude of said resistance to flow, and the electronic control alternating the direction of the flow of the DC electrical current between the probes.
  • 7. The device as defined in claim 6, and the electronic control providing for no electrical potential between the probes except when periodically directing the electrical flow there between.
  • 8. The device as defined in claim 7, and the electronic control determining the resistance between the probes by sampling the resistance there between a plurality of times and throwing out a predetermined number of the high and low samples and averaging the remaining samples for determining the sensed resistance.
  • 9. The control device as defined in claim 8, and the control not starting operation of the refrigeration system unless a predetermined period of time has elapsed since the refrigeration system was last shut off.
  • 10. The control device as defined in claim 9, and the control means stopping the operation of the refrigeration means if the temperature sensed by the temperature sensing means at the second predetermined position goes below a predetermined low temperature value.
  • 11. The control device as defined in claim 10, and the predetermined probe position providing for holding the probes so that when the ice bank forms on the evaporator coil the probes are located within the ice bank and adjacent an outer surface portion thereof.
  • 12. The device as defined in claim 6, and the electronic control having predetermined high and low resistance set points wherein the refrigeration system is operated if the sensed resistance is below the low resistance set point and wherein the refrigeration system is not operated if the sensed resistance is above the predetermined high resistance set point and wherein the operation of the refrigeration system is not changed if the sensed resistance is between the high and low resistance set points.
  • 13. The device as defined in claim 6, and the electronic control determining the resistance between the probes by sampling the resistance there between a plurality of times and throwing out a predetermined number of the high and low samples and averaging the remaining samples for determining the sensed resistance.
  • 14. The control device as defined in claim 6, and the predetermined probe position providing for holding the probes so that when the ice bank forms on the evaporator coil the probes are located within the ice bank and adjacent an outer surface portion thereof.
  • 15. The control device as defined in claim 6, and the control not starting operation of the refrigeration system unless a predetermined period of time has elapsed since the refrigeration system was last shut off.
Parent Case Info

The present application is a continuation of application Ser. No. 08/247,613 filed May 23,1994, now U.S. Pat. No. 5,732,563, which was continuation of Ser. No. 08/125,377 filed Sep. 22, 1993, now abandoned.

US Referenced Citations (3)
Number Name Date Kind
3178901 Blackett Apr 1965 A
4939908 Ewing et al. Jul 1990 A
5022233 Kirschner et al. Jun 1991 A
Non-Patent Literature Citations (2)
Entry
Savas, Computer Control of Industrial Processes McGraw-Hill Book Company, 1965, p. 12.*
Modern Dictionary of Electronics, Rudolf Graf Bobbs-Merrill Co. Inc. 1973, p. 511.
Continuations (2)
Number Date Country
Parent 08/247613 May 1994 US
Child 08/959180 US
Parent 08/125377 Sep 1993 US
Child 08/247613 US