Patent Application
20190226902
The present invention relates to a weighing apparatus such as an electronic balance or electronic scale, and more particularly, to a weighing apparatus with a flowmeter function for liquids and powders.
There has been known a weighing apparatus with a flowmeter function for accurately measuring the flow rates of liquids and powders (see, for example, Patent Literature 1).
Flow rate measurement using the weighing apparatus disclosed in Patent Literature 1 is performed as follows. For example, in weighing the amount of liquid injected into a vessel, the vessel is placed on the weighing pan of an electronic balance as a weighing apparatus, and configuration is made so that the mass of liquid injected from a tank into the vessel by a device such as a pump can be measured. A weighed value W0 at time t0 of the start of measurement is recorded.
Next, a weighed value w1 is recorded in a similar manner as described above at time t1 after the elapse of a predetermined interval (flow rate calculation cycle Δt) from time t0. In this manner, weighed values w0, w1, w2, . . . , wn at times t0, t1, t2, . . . , tn are sequentially recorded in the flow rate calculation cycle Δt. A flow rate value Qn at time tn is obtained from “the difference between a weighed value at that time and a weighed value at the preceding time.” Accordingly, the flow rate value Qn at predetermined time tn can be obtained by the equation given below:
Q
n=(wn−wn−1)/Δt
Patent Literature 1: Japanese Published Unexamined Patent Application No. 2014-137250
The flow rate calculation cycle Δt needs to be set in accordance with a flow rate and the accuracy required for its measurement, i.e., the accuracy expected for its calculated flow rate value (hereinafter referred to as “required resolution”). However, when performing measurement using the conventional weighing apparatus disclosed in Patent Literature 1, a measurer needs to calculate the flow rate calculation cycle Δt based on the flow rate to be measured and the required resolution and change settings for the weighing apparatus for every measurement, resulting in complicated operations.
A specific study about setting of the flow rate calculation cycle At with the use of a conventional weighing apparatus will be described by exemplifying a case in which a flow rate of about 6 g/min is to be measured by using an electronic balance whose minimum weighed value indication is 0.01 g with 3-digit significant figure accuracy, i.e., a resolution of 100.
Assume that in this description, the term “required resolution” means the accuracy required for a flow rate calculation value in this measurement, and the term “resolution” indicates a specific multiple of the minimum indication in the measurement to which an obtained weighed value corresponds. That is, when the minimum indication is 0.01 g and a weighed value is 1 g, the resolution is expressed as 100.
In calculating a flow rate with Δt=1 sec, since the amount of change in weighed value per sec is about 0.1 g and the minimum indication of the electronic balance is 0.01 g, the amount of change in weighed value detected becomes about 10 times the minimum indication.
Accordingly, the resolution of the calculated flow rate value is about 10. That is, the resolution is insufficient when it is required to secure 3-digit significant figure accuracy for flow rate values.
In calculating a flow rate with Δt=1 min, since the amount of change in weighed value per min is about 6 g and the minimum indication of the electronic balance is 0.01 g, the amount of change in weighed value detected becomes about 600 times the minimum indication.
Accordingly, the resolution of the calculated flow rate value is about 600. That is, the resolution is sufficient or excessive when it is required to secure 3-digit significant figure accuracy for flow rate values.
When, therefore, the flow rate calculation cycle Δt is set to make the amount of change in weighed value detected become 1 g that is about 100 times the minimum indication, it is possible to perform measurement with a resolution of 100. Obviously, the time required for the amount of change in weighed value to become 1 g is 1 g/6 g/min=10 sec, and the flow rate calculation cycle Δt should be 10 sec or more.
As described above, the flow rate calculation cycle Δt must be set depending on the flow rate to be measured and its required resolution. In manually setting a flow rate calculation cycle, when pumps whose flow rates differ are checked with a predetermined accuracy or more, it is necessary to change settings for each pump. This requires troublesome operations. In addition, in some cases, an expected accuracy may not be obtained because of a setting error. In addition, if no guideline for a flow rate is known in advance, it is necessary to repeat measuring of a flow rate and setting of a flow rate calculation cycle, resulting in complicated operations.
It is, therefore, an object of the present invention to provide a weighing apparatus with a flowmeter function allowing an easy measuring operation, which can solve the above problems and automatically set a flow rate calculation cycle.
In order to achieve the above object, a weighing apparatus with a flowmeter function according to one aspect of the present invention includes a load sensor unit configured to detect a load of a flow rate calculation target and output load signals, an A/D conversion unit configured to sequentially convert the load signals into digital load data at predetermined intervals, an arithmetic processing unit configured to sequentially convert the load data into weighed values by correction computation and calculate flow rate values from the weighed values, and a storage unit configured to sequentially store the weighed values. The arithmetic processing unit calculates amounts of change in weighed value by using the weighed values stored in the storage unit. The arithmetic processing unit calculates, based on a minimum indication of weighed values and a required resolution of weighed values, an amount of change in weighed value satisfying the required resolution. The arithmetic processing unit calculates a minimum time by which the amount of change in weighed value becomes equal to or more than an amount of change in weighed value satisfying the required resolution, sets a flow rate calculation cycle based on the time, and calculates a flow rate value based on the flow rate calculation cycle.
In the above aspect, the arithmetic processing unit is also preferably configured to set a preset required resolution value as the required resolution.
In the above aspect, the arithmetic processing unit is also preferably configured to further include an input unit for inputting a required resolution value to the arithmetic processing unit, set an input required resolution value as the required resolution and calculate an amount of change in weighed value satisfying the required resolution based on the required resolution.
In the above aspect, the arithmetic processing unit is also preferably configured to include a plurality of preset required resolution settings, with the required resolution value being input by selecting one of the plurality of required resolution settings.
In the above aspect, the arithmetic processing unit is also preferably configured to include a plurality of preset flow rate calculation cycles and set the flow rate calculation cycle by selecting, from the plurality of flow rate calculation cycles, a shortest cycle that is equal to or more than a minimum time by which the amount of change in weighed value becomes equal to or more than an amount of change in weighed value satisfying the required resolution.
According to the above configuration, changes in weighed value sequentially stored by the weighing apparatus are compared with the required amount of change determined from the required resolution of weighed values to calculate the minimum time that satisfies the required amount of change. The calculated time can be set as a flow rate calculation cycle. This can save labor of manually calculating and setting a flow rate calculation cycle in a measuring operation. This makes it possible to provide a weighing apparatus with a flowmeter function allowing an easy measuring operation, which can automatically calculate a flow rate calculation cycle.
The preferred embodiments of the present invention will be described below based on the following examples with reference to the accompanying drawings. The same reference signs denote components common to the respective examples, and a detailed description will be omitted.
The electronic balance 10 includes a load sensor unit 1, a clock unit 2, an A/D conversion unit 3, an arithmetic processing unit 4, a storage unit 5, a display unit 6, an input unit 7, and an interface unit 8.
The load sensor unit 1 is a load detection mechanism to detect a load of a weighing target. The load sensor unit 1 includes, for example, an electromagnetic balance sensor or load cell, and includes a weighing pan la on which a vessel 21 into which a liquid or powder as the weighing target is injected is placed. The load sensor unit 1 outputs an analog signal corresponding to a detected load.
The clock unit 2 is a clock generation circuit including, for example, a crystal oscillator. The clock unit 2 outputs reference time signals to the A/D conversion unit 3 and the arithmetic processing unit 4 at predetermined intervals.
The A/D conversion unit 3 is an A/D converter including an A/D conversion circuit. The A/D conversion unit 3 digitally converts analog load signals output from the load sensor unit 1 into load data at predetermined intervals based on reference time signals from the clock unit 2.
The arithmetic processing unit 4 is, for example, a microprocessor (MCU). The arithmetic processing unit 4 converts the load data output from the A/D conversion unit 3 into weighed values w1, w2, . . . , at the predetermined intervals based on reference time signals, and causes the storage unit 5 to store the weighed values. In addition, the arithmetic processing unit 4 calculates amounts Δw1, Δw2, . . . of change in weighed value by using the weighed values w1, w2, . . . stored in the storage unit 5.
Note that representative symbols concerning weighed values and the amounts of change in weighed value are respectively represented by w and Δw unless any specific time is designated.
The arithmetic processing unit 4 also sets a minimum indication B_
Note that when the A/D conversion unit 3 or arithmetic processing unit 4 incorporates a unit corresponding to the clock unit 2, the clock unit 2 need not be provided independently.
The storage unit 5 is a rewritable memory such as a RAM or flash memory, and stores various data to be used by the arithmetic processing unit 4.
The display unit 6 is, for example, a liquid crystal display. The display unit 6 displays data such as weighing results, display information required for settings, and the like.
The input unit 7 is, for example, a key switch. A measurer can input commands such as so-called “perform taring,” “output weighed value,” and “select flow rate calculation mode” and various settings such as “required resolution” with this key switch.
Note that the display unit 6 and the input unit 7 may be integrated to be provided as a touch panel input unit.
The interface unit 8 is an interface used for connection to an external device such as a personal computer (not illustrated). The electronic balance 10 is configured to be connected to an external device via the interface unit 8. Accordingly, the electronic balance 10 outputs measured data to an external device and receives commands from an external device via the interface unit 8.
When the electronic balance 10 measures the flow rate of liquid injected into the vessel 21 by a pump 23, for example, the electronic balance 10 is arranged such that the liquid contained in a tank 22 is injected by the pump 23 into the vessel 21, as illustrated in
Next, processing operations performed by the arithmetic processing unit 4 when the flow rate calculation cycle ΔT is automatically set and flow rate calculation is performed by using electronic balance 10 will be described with reference to
When the flow rate measurement mode starts, the process shifts to step S101, in which the arithmetic processing unit 4 sets the preset minimum indication B_
Next, when the process shifts to step S102, the arithmetic processing unit 4 sets the storage interval T_
Next, when the process shifts to step S103, the arithmetic processing unit 4 sets a preset required resolution value F_
Next, when the process shifts to step S104 and a required resolution value F_
W_
If no required resolution is newly input from the input unit 7 in step S104 (NO in step S104), the process shifts to step S106 in which the arithmetic processing unit 4 calculates the amount W_
Next, when the process shifts to step S107, the arithmetic processing unit 4 determines whether a time corresponding to the predetermined storage interval T_
Processing in steps S107, S109, and S110 to be performed when the predetermined storage interval T_
As described above, the maximum value T_
The arithmetic processing unit 4 sequentially stores the weighed values w in the storage areas Mn to M0 at storage intervals T_
Next, when the process shifts to step S110, the new weighed value w0 is stored in the storage area M0. In this manner, weighed values sampled at the storage intervals T_
Referring back to
Next, when the process shifts to step 5112, the arithmetic processing unit 4 calculates an amount Δw1 of change in weighed value, based on equation (II) given below:
Δwi=|wi−w0| (II)
In this case, because i=1, Δw1=|w1−w0|.
Next, when the process shifts to step S113, the arithmetic processing unit 4 compares the amount Δw1 of change in weighed value with the amount W_
Δwi≥W_
When inequality (III) is satisfied (YES in step S113), the process shifts to step S116 in which the arithmetic processing unit 4 calculates i×T_
When inequality (III) is not satisfied (NO in step S113), the process shifts to step S114 in which the arithmetic processing unit 4 determines whether the value i of the counter for the calculation of the flow rate calculation cycle Δt and a value n of the counter corresponding to the maximum value T_
i=n (IV)
When equation (IV) is not satisfied (NO in step S114), the process shifts to step S115, in which the arithmetic processing unit 4 to increment the counter to set i=i+1. The process then returns to step S112.
In this manner, while incrementing the counter, the arithmetic processing unit 4 repeats steps S112 to S115 until the amount Δwi of change in weighed value becomes equal to or more than the amount W_
When it is determined in step S114 that equation (IV) is satisfied (YES in step S114), the process shifts to step S118, in which the arithmetic processing unit 4 sets the maximum value T_
When the flow rate calculation cycle Δt is set in step S117 or S118, the process shifts to step S119, in which the arithmetic processing unit 4 calculates the amount Δw of change in weighed value corresponding to the time Δt, based on the set flow rate calculation cycle Δt.
Next, when the process shifts to step S120, the arithmetic processing unit 4 calculates a flow rate value Q based on equation (V) given below:
Q=Δw/Δt (V)
The arithmetic processing unit 4 then displays the calculated flow rate value Q on the display unit and terminates the processing. Note that the flow rate value Q may be output to an external device as needed.
Note that the process may omit step S103 and shift to step S104, in which arithmetic processing unit 4 sets the required resolution F_
Steps S114 and S118 are simply provided to set flow rate calculation cycle Δt by regarding the maximum value T_
According to the above configuration, the weighing apparatus can compare the sequentially stored amount Δw of change in weighed value with the required amount W—SPC of change determined from the required resolution F_
When the initial required resolution value F_
Even if the flow rate changes during measurement, since the flow rate calculation cycle Δt can be automatically changed in accordance with the change, it is possible to continue measurement satisfying a predetermined required resolution without repeatedly resetting the flow rate calculation cycle Δt for each change. This can facilitate a measuring operation. This provides, in particular in the case of using a pump that can cause a change in flow rate such as pulsation, a guide for the observation of the degree or cycle of the pulsation by monitoring a change in Δt over time.
When the measurer manually sets the flow rate calculation cycle Δt in accordance with pumps with different flow rates or a change in flow rate as in the conventional art, artificial errors can occur in reading of the flow rate value Q, calculation of the flow rate calculation cycle Δt, and setting of the flow rate calculation cycle Δt. In contrast to this, according to the above configuration, even if the measurer inputs a required resolution setting, he/she does not perform any operation other than inputting a required resolution setting. When the measurer inputs no required resolution setting, it is possible to automatically set the flow rate calculation cycle Δt without requiring any operation by the measurer. Therefore, the occurrence of artificial errors concerning the flow rate calculation cycle Δt is greatly reduced.
A weighing apparatus according to the second example is an electronic balance having the same mechanical configuration as that of the electronic balance 10 according to the first example. However, the second example differs from the first example in that an arithmetic processing unit 4 has a plurality of required resolution settings saved in advance.
For example, as illustrated in
The apparatus may also be configured so that a display unit 6 displays the required resolution settings of the three levels, namely, “accuracy priority,” “standard setting,” and “response speed priority,” instead of the settings preset for the input unit 7, to enable the measurer to select one of the required resolution settings of the three levels displayed on the display unit 6, thereby allowing the measurer to input the required resolution value F_
The apparatus may also be configured to set the value “100” corresponding to “standard setting” as an initial required resolution value F_
In this case, the measurer selects “accuracy priority” when the accuracy of measurement is prioritized for long-term treatment at a small flow rate , for example, when using an infusion pump. The measurer selects “standard setting” when, for example, measuring the capacity of a pump. The measurer selects “response speed priority” when measuring the degree or cycle of pulsation.
According to the above configuration, it is possible to easily input a required resolution and set a proper flow rate calculation cycle in accordance with the purpose of measurement regardless of the skill level of a measurer.
A weighing apparatus according to the third example is an electronic balance with the same mechanical configuration as that of the electronic balance 10 according to the first example, but is configured to select a flow rate calculation cycle Δt from a plurality of cycles Δt1, Δt2, Δt3, . . . , Δtj preset for the weighing apparatus. The maximum value of selectable cycles is a maximum value T_
The processing operations performed by the arithmetic processing unit 4 will be described with reference to
Processing in steps S201 to S216 and S222, from the start of a flow rate calculation mode to the calculation of a minimum time T_
When the process shifts to step S217, the arithmetic processing unit 4 sets a counter for the selection of the flow rate calculation cycle Δt to j=1. The process then shifts to step S218 to determine whether the shortest cycle Δt1 of a plurality of cycles is equal to or more than the minimum time T_
T_
When inequality (VI) is satisfied (YES in step S218), the process shifts to step S220, in which the arithmetic processing unit 4 selects the shortest cycle Δt1 of the plurality of cycles as the shortest cycle Δtm satisfying T_
When the process returns to step S218, the arithmetic processing unit 4 determines again whether the time T_
In this manner, the arithmetic processing unit 4 selects the shortest cycle Δtm equal to or more than the time T—SPC by which one of amounts Δw1, Δw2, . . . of change in weighed value becomes equal to or more than the amount W_
Next, when the process shifts to step S221, the arithmetic processing unit 4 sets, as the flow rate calculation cycle Δt, the shortest cycle Δtm equal to or more than the time T_
Next, in step S223, the arithmetic processing unit 4 recalculates an amount Δw of change in weighed value corresponding to the time Δt based on the flow rate calculation cycle Δt set in step S221 or S222.
Next, when the process shifts to step S224, the arithmetic processing unit 4 calculates a flow rate value Q based on equation (VII) given below:
Q=Δw/Δt (VII)
and displays the calculated flow rate value Q. The arithmetic processing unit 4 then terminates the processing.
According to the above configuration, since the flow rate calculation cycle Δt to be set is selected from the plurality of preset cycles Δt1, Δt2, Δt3, . . . , Δtj, a round number can be set as the flow rate calculation cycle Δt. When approximate flow rates are to be measured, in particular, the same flow rate calculation cycle is set for each flow rate calculation cycle setting, and hence measurement can be performed with high repeatability while a flow rate calculation cycle is set in accordance with a flow rate.
Although each of the above cases has exemplified the measurement of the flow rate of liquid injected into the vessel 21 placed on the weighing pan 1a, measurement targets are not limited to liquids but may include powders. In addition, the weighing apparatus according to each embodiment may be configured to measure the flow rate of liquid discharged from a vessel placed on the weighing pan 1a or the amount of change in material evaporating or vaporizing from a vessel placed on the weighing pan 1a.
Although the preferred embodiments of the present invention have been described, the above examples are examples of the present invention. These embodiments can be combined based on the knowledge of a person skilled in the art. Such combined embodiments are incorporated in the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-009647 | Jan 2018 | JP | national |
