JPS61189421A - Zero point adjusting circuit - Google Patents

Abstract

PURPOSE:To adjust a zero point completely automatically within a short period by controlling the outputs of the zero point rough adjusting circuit and a zero point fine adjusting circuit by a microcomputer to compensate the zero point of a weighing machine. CONSTITUTION:An output signal from a rough adjusting D/A converter D1 is sent to a terminal B of a rough adjusting subtractor 51 through a level shifting circuit 13 to calculate A-B and the subtracted result is inputted to the terminal C of a fine adjusting subtractor 52 through an amplifier alpha1. On the other hand, the output from a fine adjusting D/A converter D2 is inputted to the terminal D of the circuit 52 through a level shifting circuit 14. The output of the circuit 52 is inputted to an A/D converter 8 through one of sample holding circuits 61, 62 and the output of the converter 8 is inputted to a weight monitoring microcomputer 15. The input signal is stored in a RAM16 as the zero point of each weighing machine. A microcomputer 17 for combining operation reads out the weight of each commodity which is weighted by each computer from the RAM16 and selects the optimum combination for a set point.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zero point adjustment circuit for electronic scales, combination weighing devices, and the like.

(Prior art) In a weighing device using a weight detector consisting of a load cell, the weight signal of the detected product is input to an A/D converter through an amplifier, a filter, etc., and the signal converted to a digital signal is The information is transmitted to a computer and predetermined arithmetic processing is performed.

In weighing machines that use such load cells and amplifiers, the characteristics of the load cells and amplifiers change depending on the temperature, and in combination weighing devices that use weighing hoppers, the tare weight value changes due to the adhesion of product residue. However, a problem arises in that highly accurate measurement is no longer possible.

For this reason, conventionally, a zero point adjustment circuit has been provided to deal with this problem. This zero point adjustment involves (1) rough adjustment to bring the output caused by the initial load of the weighing pan or weighing hopper to approximately zero level, and (2) zero point adjustment due to temperature drift or adhesion of the object to be weighed to the hopper. Fine adjustments were used to correct misalignments. Among these, the zero point correction by adjustment (2) was previously proposed by the applicant in Japanese Patent Application No. 74831/1983.

FIG. 4 shows an example in which such a conventional zero point correction circuit is used in a combination weighing device. In FIG. is input. When a timing signal is input from a packaging machine or the like to the microcomputer 15, weight signals are sequentially read from the multiplexer according to a switching signal and input to the wood tone subtractor 5. On the other hand, when setting the microcomputer to the automatic zero point adjustment mode and performing zero point adjustment, the microcomputer first reads the zero point correction value Bl of the first weighing machine from the memory, and uses this as the The signal is outputted to the A converter 10 and subjected to D/A conversion, and the output value is inputted to the wood tone subtractor 5 through the voltage dividing circuit 13. The subtracter 5 subtracts the empty weight value of the first weighing machine and the correction value of the voltage dividing circuit 13 to obtain a difference, which is sent to the microcomputer through the sample hold circuit 6 and the A/D converter 8. It is also input to the comparator 7. The microcomputer converts the D/A converter 1 according to the output value of the comparator.
A/D converter 8 increases or decreases the zero point correction value B output to
control so that the output value of is a predetermined value. These processes are performed sequentially for each measuring instrument to perform zero point correction.

Note that the span correction reference values U1 to Un are stored in the memory, and these are sequentially read out when inputting the weight signal of each weighing machine and output to the span D/A converter 11. Also, when the span switch 9 is turned on and the microcomputer is set to the span adjustment mode, the span correction reference value U1''Un of the corresponding weighing machine is changed to the span D/
The voltage is output to the A converter 11, and the output of the D/A converter 11 is applied as a reference voltage to the A/D converter 8 via the voltage division shift circuit 12. Then, a predetermined span adjustment is performed by increasing or decreasing the span correction reference values U1 to Un so that the output signal G of the A/D converter 8 becomes a predetermined value.

(Problems with conventional technology) In this way, the conventional fine adjustment of zero point adjustment corrects the output level of the amplifier so that the weight value becomes a predetermined value when the weighing instrument, etc. is not loaded. Zero point adjustment is performed with high accuracy.

However, since the coarse adjustment of the zero point adjustment has an extremely wide adjustment range, the adjustment has conventionally been carried out exclusively manually using a variable resistor. For this reason, it takes a considerable amount of time and effort to make rough adjustments, and especially in systems that are equipped with multiple weighing machines, such as combination weighing devices, coarse adjustments must be made for each weighing machine. There was a problem in that the adjustment work was quite troublesome.

(Objective of the Invention) The present invention aims to solve the problems of the prior art, and is capable of fully automatic zero point adjustment, including rough adjustment, in a short time, and which can be used in a combination weighing device. The purpose of this invention is to provide a zero point adjustment circuit that can reduce the number of parts compared to the conventional one.

(Summary of the Invention) The zero point adjustment circuit of the present invention inputs the empty weight value, which is the output signal of the weighing machine under no load, into a microcomputer and performs the zero point correction of the weighing machine. A fine adjustment circuit is provided, and the output signals of the coarse adjustment circuit and the fine adjustment circuit are controlled by a microcomputer to correct the zero point of the weighing machine.

Further, this zero point adjustment circuit performs zero point adjustment of all the weighing machines constituting the combination weighing device (Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram when the present invention is used in a combination weighing device. In the present invention, a zero point fine adjustment D/A converter D2 and a zero point coarse adjustment D/A converter D[ It is distinctive in that it has been established. When performing zero point adjustment according to a command from the weight monitoring microcomputer, the empty weight of a predetermined weighing machine is inputted to the A terminal of the coarse adjustment subtraction circuit 5 through a multiplexer. In addition, the preset values to be set in each D/A converter DI and D2 are read from the memory RAM 16, and 1, for example, the upper 8 bits are set to the D/A converter for rough adjustment, and the lower 8 bits are set to the D/A converter for rough adjustment.
Input the bits to the fine adjustment D/A converter. Coarse adjustment D/A
The output signal of the converter is passed through the level shift circuit 13,
It is input to the B terminal of the coarse adjustment subtraction circuit 51. The coarse adjustment subtraction circuit performs the calculation A-H, and inputs the signal to the C terminal of the fine adjustment subtraction circuit through the amplifier αl. This amplifier αl makes it possible to cope with changes in the weight of each weighing machine.

On the other hand, the output signal of the fine adjustment D/A converter is inputted to the D terminal of the fine adjustment subtraction circuit 52 through the level shift circuit 14. The adjustment width ratio at this time is each D/A converter D l +
For example, α1 and β1 according to the weight per bit of 02.
:β2=256:1. The output signal of the subtraction circuit for fine adjustment is sent to the sample hold circuit 6. ．． 62, the signal passes through the A/D converter 8, and is inputted to the 1 weight monitor microcomputer. This input signal is stored in the RAM 16 as the zero point of each weighing machine. In addition, when the span switch of the remote control box 18 is turned on,
Span adjustment similar to the conventional example is performed under the control of the weight monitor microcomputer. Further, the one combination calculation microcomputer 17 reads out the weight of the product weighed by each weighing machine from the RAM 16, and selects the optimal combination for the set value. D/A converter D2
For example, the adjustment width ratio is set to α so that the maximum variable width is
1 ・βl: If set to β2=128: D for rough adjustment
Even if there is an error equivalent to ±1/2 LSB in the variable width of the /A converter, this can be supplemented by the subsequent fine adjustment D/A converter D2.

FIGS. 2 and 3 are flowcharts showing the processing procedure of the present invention.

FIG. 2 is a flowchart for the initial zero point adjustment when the span of the weighing machine is not determined. In this case, the zero point coarse adjustment and fine adjustment are performed at the same time.

(1) Step P to specify the weighing machine that performs zero point adjustment
1) Next, output a switching signal to the multiplexer to switch to the designated weighing machine, 2 (Step P2) output a value of 1/2 of the maximum input value to the span adjustment D/A converter D3 (Step P3), In other words, if the maximum input value is 1 in all bits, a value with only the most significant bit set to 1 is output.
Next, a sample hold command signal is output (step P
4).

(2) Total number of bits of D/A converters for coarse adjustment and fine adjustment (
In this example, it is set to 16) j is set to 16 (step P5
)0 Next, the upper 8 bits B1 and lower 8 bits B2 of the 16-bit binary code B are set to 0 (step P
s).

(3) (B+2”) with D/A converter D l for zero point adjustment
+ D 2, input the A/D converter output, and store it in memory (step 2). Next, the target zero point Nz is compared with the memory value N (output value of the A/D converter) (step Ps). If the condition of Nz≧N is satisfied, the binary code B is converted to CB + 2- i-'
), the total number of bits j of the D/A converter is subtracted by 1 (step Plt), and thereafter, the processes of steps P7 to ptt are repeated until j=O (step P12) 11 (4) The upper 8 bits of binary code B are stored as the coarse adjustment bias value of the specified weighing machine, and the lower 8 bits are
The bit is stored as the bias value for fine adjustment of the weighing machine,
Furthermore, the output of the A/D converter at that time is stored as the zero point (step P 1ys) *Check that the specification has been completed for all weighing machines (step P14), but for the weighing machines that have not been completed, this Specify step Pl
! S), repeat the processing of steps P2 to P13.

In the above process, the zero point is roughly adjusted and finely adjusted for each weighing machine, but when the initial loads of each weighing machine are approximately equal,
It is also possible to perform coarse adjustment and fine adjustment only for the first weighing machine, and apply only the fine adjustment to the next weighing machine by applying the coarse adjustment bias value B1 obtained in the first coarse adjustment. Also, if the minimum adjustment width is set below ILsB of the A/D converter output,
Although the NZ can be set as the zero point, the adjustment range is coarse, and even if the output N of the A/D converter at the end of the zero point adjustment is N=Nz, the adjusted A/D
If the output N of the converter is read and stored as a zero point, no error will occur when calculating the net weight.

FIG. 3 is a flowchart showing a processing procedure for correcting zero drift after completion of span adjustment and zero point adjustment. In this case, coarse adjustment of the zero point is not necessary, so the total number of bits j of the zero point adjustment D/A converter is 8, and the binary code is only the lower bit B2, so the coarse adjustment bias value The same process as that shown in Fig. 2 is performed except that the output of B1 is no longer required.However, if only one weighing machine is specified and zero point adjustment is performed between weighing operations, step 515 and ste processing becomes unnecessary.

In addition, the reason why the zero point adjustment circuit is divided into a coarse adjustment circuit and a fine adjustment circuit is that two (2) 8-bit D/A converters, which are cheaper than using one expensive 16-bit D/A converter, are used. This is because it can be manufactured much more cheaply if it is used.

In addition, for weighing devices such as electronic scales other than combination weighing devices,
The zero adjustment circuit of the present invention can be used.

(Effects of the Invention) As explained above, according to the present invention, the following effects can be obtained.

(1) In the combination weighing device, all zero point adjustment circuits, including coarse and fine adjustment, are provided after the multiplexer, so compared to the conventional method, which had a coarse zero point adjustment circuit for each weighing machine, the accuracy is much improved. The number of parts can be reduced.

(2) Since coarse adjustment and fine adjustment of the zero point can be simultaneously and automatically performed by a computer in a short time, manual adjustment work can be eliminated.

(3) When the initial loads of each weighing machine are approximately equal (the outputs of the load cells are approximately equal), only the first one is subjected to coarse and fine adjustment, and the bias value obtained from the first coarse adjustment is used from the next weighing machine. B
By applying mutatis mutandis, the subsequent rough adjustment can be omitted, so
Adjustment work can be shortened.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of the present invention, and FIG. 2 is a schematic block diagram of the present invention. FIG. 3 is a flowchart, and FIG. 4 is a block diagram of a conventional example. l...load cell, 2...amplifier, 3...filter. 4... Multiplexer, 5... Subtraction circuit, 6...
Sample hold circuit, 8...A/D converter, DI
+ B2... D/A converter for zero point adjustment, B3... D/A converter for span, 12... Subtraction circuit, 13...
Level shift circuit, 14...Level shift circuit, 15
...Microcomputer, 16...Memory, 17
...Microcomputer for combinational calculations, 18...
Remote control pocket. Patent applicant: Ishida Kouki Seisakusho Co., Ltd. Agent Patent attorney Minoru Tsuji Procedural amendment (voluntary) May 19, 1985 1985 Patent application No. 031339 2, Title of invention Zero point adjustment circuit 3, Person making the amendment Relationship to the case Patent applicant 4, agent address 3-146 Kanda Ogawa-cho, Chiyoda-ku, Tokyo 101
, The entire text of the specification to be amended and Drawing 7, Contents of the amendment (1) The entire text of the specification will be corrected as shown in the attached sheet. (2) Figures 1, 3, and 4 are corrected as shown in the attached sheet. (3) Change Figure 2 to Figure 2(a) and add Figure 2(b). Description 1. Title of the invention Zero point adjustment circuit 2. Claims (1) In a device that performs zero point correction of a weighing machine by inputting an empty weight value, which is an output signal of a weighing machine under no load, into a microcomputer. , a zero point coarse adjustment circuit and a fine adjustment circuit are provided, and the output signals of these coarse adjustment circuit and fine adjustment circuit are controlled by a microcomputer to correct the zero point of the weighing machine. Circuit. (2) The zero point adjustment circuit according to claim (1), which performs zero point adjustment of all the weighing machines constituting the combination weighing device. 3. Detailed description of the invention (industrial) Field of Application) The present invention relates to a zero point adjustment circuit in an electronic scale, a combination weighing device, etc. (Prior Art) In a weighing device using a weight detector consisting of a load cell, the weight signal of the detected product is transmitted to an amplifier, The signal is input to an A/D converter through a filter, etc., converted into a digital signal, and transmitted to a microcomputer, where predetermined arithmetic processing is performed. The characteristics of the weighing hopper and amplifier change depending on the temperature, and in a combination weighing device that uses a weighing hopper, product residue and the like adhere to it, causing a problem in that the tare weight value changes and highly accurate weighing becomes impossible. Therefore, in the past, a zero point adjustment circuit was installed to deal with this problem.This zero point adjustment involves: (1) A rough method that reduces the output caused by the initial load of the weighing pan, weighing hopper, etc. to approximately zero level. adjustment, and (2) fine adjustment to correct for zero point deviations due to temperature drift or adhesion of objects to be weighed to the hopper. Of these, zero point correction by adjustment (2) is particularly important. The applicant had previously proposed this in Application No. 58-74831. Figure 4 shows an example of using such a conventional zero point correction circuit in a combination weighing device. The weight signal from the weighing machine is input to the multiplexer 4 through the amplifier 2 and the filter 3. When the timing signal is input from the packaging machine etc. to the microcomputer 15, the weight signal is sequentially read from the multiplexer by the switching signal, and the The zero point correction value B of the first weighing machine is input to the adjustment subtracter 5. On the other hand, when setting the microcomputer to automatic zero point adjustment mode and performing zero point adjustment, the microcomputer first stores the zero point correction value B of the first weighing machine in its memory. 16 and outputs it to the D/A converter 10 for D/A control.
A conversion is performed, and the output value thereof is input to the subtracter 5 for electrical adjustment through the voltage dividing circuit 13. The subtracter 5 subtracts the empty weight value of the first weighing machine and the correction value from the voltage dividing circuit 13 to obtain a difference, which is then sent to the sample hold circuit 6 and the A/D
The signal is input to the microcomputer through the converter 8 and is also input to the comparator 7. The microcomputer 15 controls the D/D according to the output value of the comparator tough.
The zero point correction value B1 output to the A converter 10 is increased or decreased, and the A/
The output value of the D converter 8 is controlled to be a predetermined value. These processes are performed sequentially for each weighing machine to perform zero point correction. Note that the memory 16 stores span correction reference values U1 to Un, which are sequentially read out when inputting the weight signal of each weighing machine and output to the span D/A converter 11. . Further, when the span switch 9 is turned on and the microcomputer 15 is set to the span adjustment mode,
The span correction reference value Ul - Un of the applicable weighing machine is output to the span D/A converter 11, and the output of the D/A converter 11 is sent to the A/D converter via the partial voltage shift circuit 2. It is applied as a reference voltage of 8. Then, a predetermined span adjustment is performed by increasing or decreasing the span correction reference values U1 to Un so that the output signal G of the A/D converter 8 becomes a predetermined value. (Problems with conventional technology) In this way, the conventional fine adjustment of zero point adjustment corrects the output level of the amplifier so that the weight value becomes a predetermined value when the weighing pan etc. is not loaded. Zero point adjustment is performed with high accuracy. However, since the coarse adjustment of the zero point adjustment has an extremely wide adjustment range, the adjustment has conventionally been carried out exclusively manually using a variable resistor. For this reason, it takes a considerable amount of time and effort to make rough adjustments, and especially in systems that are equipped with a large number of weighing machines, such as combination weighing devices, coarse adjustments must be made to each weighing boat. There was a problem in that the adjustment work was quite troublesome. (Objective of the Invention) The present invention aims to solve the problems of the prior art, and is capable of fully automatic zero point adjustment, including rough adjustment, in a short time, and which can be used in a combination weighing device. The purpose of this invention is to provide a zero point adjustment circuit that can reduce the number of parts compared to the conventional one. (Summary of the Invention) The zero point adjustment circuit of the present invention inputs the empty weight value, which is the output signal of the weighing machine under no load, into a microcomputer and performs the zero point correction of the weighing machine. A fine adjustment circuit is provided, and the output signals of the coarse adjustment circuit and the fine adjustment circuit are controlled by a microcomputer to correct the zero point of the weighing machine. Further, this zero point adjustment circuit performs zero point adjustment of all the weighing machines constituting the combination weighing device. (Example) An example of the present invention will be described below with reference to FIG. FIG. 1 is a circuit diagram when the two aspects of the present invention are used in a combined weighing device. The present invention is characterized in that a D/A converter D2 for zero point fine adjustment 1 and a D/A converter D2 for zero point coarse adjustment are provided. Microcomputer 15 for weight monitor
When performing zero point adjustment according to a command from the weighing machine, the empty weight of a predetermined weighing machine is inputted to the A terminal of the coarse adjustment subtraction circuit 51 through the multiplexer 4. In addition, the preset value to be stored in D2 of each D/A converter is read from the memory RAM 16, and the upper 8 bits are used for coarse adjustment, and the lower 8 bits are used for fine adjustment. input to the D/A converter D2. The output signal of the rough adjustment D/A converter D1 is inputted to the B terminal of the coarse adjustment subtraction circuit 51 through the level shift circuit 13. The coarse adjustment subtraction circuit 51 performs the calculation of A-H, and the fine adjustment subtraction circuit 52 calculates C through the amplifier α1.
Input the signal to the terminal. This amplifier α1 makes it possible to cope with changes in the weight of each weighing machine. On the other hand, the output signal of the fine adjustment D/A converter D2 is as follows. D of the fine adjustment subtraction circuit 52 through the level shift circuit 14
input to the terminal. The adjustment width ratio at this time is. For example, it is set to αl·βl:β2=256:1 depending on the weight per bit of each D/A converter DI+D2. The output signal of the fine adjustment subtraction circuit 52 is sent to the sample hold circuit 6. ．． 62 to the A/D converter 8, and then to the weight monitor microcomputer 15.
is input. This input signal is stored in the RAM 16 as the zero point of each weighing machine, and when the span switch of the remote control box 18 is turned on, the span adjustment D/A
The output of the converter D3 is applied as a reference voltage to the A/D converter 8 via the subtraction circuit 12, and the span adjustment is performed under the control of the weight monitoring microcomputer 15 as in the conventional example. Further, the one combination calculation microcomputer 17 reads out the weight of the product weighed by each weighing machine from the RAM 16, and selects the optimum combination for the set value. In addition, 2LS of the rough adjustment D/A converter D1
For example, the adjustment width ratio is set to α1·βl : β2=1 so that the range that can be varied with a variation width equivalent to B (twice the least significant bit) becomes the maximum variation width of the fine adjustment D/A converter D2.
If set to 28:l, even if there is an error equivalent to ±1/2 LSB in the variable width of the coarse adjustment D/A converter DI, this can be compensated for by the subsequent fine adjustment D/A converter D2. . FIGS. 2(a), 2(b), and 3 are flowcharts showing the processing procedure of the present invention. Figure 2 (a) is a flowchart for the initial zero point adjustment when the span of the weighing machine is not determined.
In this case, coarse adjustment and fine adjustment of the zero point are performed simultaneously. (1) Step P to specify the weighing machine that performs zero point adjustment
1), then output a switching signal to the multiplexer to switch to the designated weighing machine (step P2), and then
A value of 1/2 of the maximum input value is output to the converter D3 (step P3). That is, if the maximum input value is 1 in all bits, a value with only the most significant bit set to 1 is output. Next, a sample hold command signal is output (step P
4). (2) Total number of bits of D/A converters for coarse adjustment and fine adjustment (
In this example, it is set to 16) je16 (step P5
)0 Next, the upper 8 bits B1 and lower 8 bits B2 of the 16-bit binary code B are set to 0 (step P
6). (3) (B+2j-1) is a D/A converter D for zero point adjustment.
Step P7), A/D
Store the output N of the converter 8 in the memory 16 (step 2
Day). Next, in step P, the target zero point Nz is compared with the value N stored in the memory 16 (output value of the A/D converter).
g), if the condition of Nz≧N is not satisfied, change the binary code B to (B+2J) (step Plo), and set each D
/The total number of bits j of A converters Dl and D2 is subtracted by 1 (
Step P. 1), After that, repeat the processing of steps P7 to P11 until j=O (step P12) II (4) Store the upper 8 bits B□ of binary code B as the rough adjustment bias value of the specified weighing machine, and The 8-bit B2 is stored as a bias value for fine adjustment of the weighing machine, and the output of the A/D converter 8 at that time is stored as a zero point (step P!3). Check that the specification has been completed for all weighing machines (Step P14), specify this for the weighing machines that have not been completed (Step P15), Steps P2 to T''t3
Repeat the process. The above process performs coarse and fine adjustment of the zero point for each weighing Isobune, but when the initial loads of each weighing machine are approximately equal,
It is also possible to perform coarse adjustment and fine adjustment only for the first weighing machine, and apply the coarse adjustment bias value B obtained in the first coarse adjustment to the next weighing machine, and perform only fine adjustment. However, the initial load of each weighing hopper is 2L of the rough adjustment D/A converter D1.
Considering the possibility that the fluctuation is within the range equivalent to SB, the fine adjustment D/A converter D2 is replaced by the coarse adjustment D/A converter D1.
It is necessary to provide in advance an adjustment range that covers a range equivalent to 2LSB. The flowchart in Figure 2(b)
By changing steps P5 to P13 in Figure (a), coarse adjustment and fine adjustment are performed only for the first weighing machine, and from the primary weighing machine, the coarse adjustment bias value B1 obtained in the first coarse adjustment is applied mutatis mutandis. This is the procedure for performing wood toning. First, the number of bits j of the rough adjustment D/A converter D1 is set to 8 (step P2 t). Next, the upper 8 bits B1 of the 16-bit binary code B are set to 0, and the lower 8 bits B2 are set to 26 as a bias. (Step P22), and output this bias value B2 to the fine adjustment D/A converter D2 (Step P25), (B,
+2j-') is output to the coarse adjustment D/A converter n, step P24), and the output N of the A/D converter 8 is stored in the memory 16.
(Step P25) a Next, the target zero point Nz and the value stored in the memory 16 N (A/
Step P26), N
If the condition Z≧N is not satisfied, binary code B1
(B, +2) Step P27), and subtract 1 from the number of bits j of the D/A converter Dl (Step 22)
, thereafter, the processes of steps P24 to P2B are repeated until j=0 (step P29). In this way, the coarse adjustment D/A
An input bias value B1 for the transducer is determined and the input bias value B1 for the transducer is determined. After outputting B1 (step 3°), fine adjustment D/A
Determine the input bias value B2 of converter D2. That is, the number of bits j of the fine adjustment D/A converter D2 is set to 8 (step P5□). Next, the lower 8 bits B2 of the binary code B are set to 0 (step Fi2), and (B2+2) is output to the fine adjustment D/A converter D2 (step P3g), and the output of the A/D converter 8 is N is stored in the memory 16 (step P34). Next, the target zero point Nz is compared with the stored value N (output value of the A/D converter) in the memory 16. Step Pg5), Nz≧
If the condition of N is not satisfied, the binary code B2 is changed to (
B2+2''-'), step P56), and subtract 1 from the bit number j of D/A converter D2 (step P57).
After e, repeat steps pgg to P57 until j=o (step 23), thus storing B as the bias value of the rough adjustment D/A converter D1,
The fine adjustment bias value B2 of the weighing machine specified one after another can be determined and stored (step Ps s ) e
As a result, for example, even if the initial load of the weighing hopper of each weighing machine deviates within the adjustment range equivalent to 2 LSB of the rough adjustment D/A converter D1, the coarse adjustment D/A converter D! The output value of can be fixed at the adjustment value determined for a specific weighing machine, and zero point adjustment for other weighing machines is realized only by adjustment by the fine adjustment D/A converter D2. Also,
If the minimum adjustment width is set below the ILSB of the output of the A/D converter 8, the Nz can be set to zero. Even if the adjustment range is coarse and the output N of the A/D converter 8 at the end of the zero point adjustment is N=Nz, the adjusted output N of the A/D converter 8 should be read again after the zero point adjustment is completed. , if this is stored as a zero point, a time difference in calculating the net ffi amount calculation ratio will not occur. FIG. 3 is a flowchart showing a processing procedure for correcting zero drift after completion of span adjustment and zero point adjustment. In this case, as in the case of FIG. 2(b), coarse adjustment of the zero point is not necessary, so the zero point adjustment D/A converter D
The total number of bits j of I + D 2 is 8, and
Since the binary code also includes only the lower bit B2, there is no need to output the rough adjustment bias value B1. In addition, when only one weighing machine is designated and zero point adjustment is performed between weighing operations, the processes of step S15 and StS are unnecessary. Furthermore, the reason why the zero point adjustment circuit is divided into a coarse adjustment circuit and a fine adjustment circuit is to use two 8-bit D/A converters, which are cheaper than one expensive 16-bit D/A converter. This is because it can be produced much more cheaply. In addition, for weighing devices such as electronic scales other than combination weighing devices,
The zero adjustment circuit of the present invention can be used. (Effects of the Invention) As explained above, according to the present invention, the following effects can be obtained. (1) In the combination weighing device, all zero point adjustment circuits, including coarse and fine adjustment, are provided after the multiplexer, so compared to the conventional method, in which each weighing boat had a coarse zero point adjustment circuit, it is much more effective. The number of parts can be reduced. (2) Since coarse adjustment and fine adjustment of the zero point can be simultaneously and automatically performed by a computer in a short time, manual adjustment work can be eliminated. (3) When the initial loads of each weighing machine are approximately equal (the outputs of the load cells are approximately equal), coarse and fine adjustment is performed for only the first one, and the first coarse adjustment is used for the next weighing machine. By applying the bias value B1, subsequent rough adjustment can be omitted, so the adjustment work can be shortened. 4. Brief description of the drawings ff11 is a schematic block diagram of the present invention, FIG. 2(a)
, (b), FIG. 3 is a flowchart, and FIG. 4 is a block diagram of a conventional example. l...Load cell, 2...Amplifier, 3...Filter, 4...Multiplexer, 5...Subtraction circuit, 6...
...Sample hold circuit, 8...A/D converter, D
l, D2... D/A converter for zero point adjustment, D3...
Span D/A converter, 12... Subtraction circuit, 13...
・Level shift circuit, 14...Level shift circuit, 1
5...Microcomputer, 16...Memory, 1
7...Microcomputer for combinational calculations, 18...
・Remote control box.

Claims (2)

[Claims] (1) In a device that inputs the empty weight value, which is the output signal of the weighing machine under no load, into a microcomputer and performs zero point correction of the weighing machine, a coarse zero adjustment circuit and a fine adjustment circuit are provided. A zero point adjustment circuit, characterized in that output signals of a coarse adjustment circuit and a fine adjustment circuit are controlled by a microcomputer to correct the zero point of a weighing machine. (2) The zero point adjustment circuit according to claim (1), which performs zero point adjustment of all weighing machines constituting the combination weighing device.