JPH0562283B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The disclosed technology relates to improvement of an A/D converter in an electronic balance. <Prior Art> There are various types of electronic scales that differ in weighing capacity, weighing accuracy, and the like. For this reason, in order to avoid rising manufacturing costs due to high-mix, low-volume production,
For example, weight sensors use the same type of load cells and the same type of A/D converters that convert their output analog signals into digital signals, allowing common parts and reducing the number of parts. We are trying to make this happen. However, in order to change the weight value without reducing the resolution of the A/D converter, it is necessary to adjust the input level to the A/D converter, and for this reason, in the past, an amplifier circuit was required according to each specification. And so. For example, a load cell designed to have an output voltage of 20mV when loaded with 20Kg and a double-integration A/D converter designed to have a maximum input voltage of 2V can be used to perform weighing. are 5 each
When manufacturing Kg, 10Kg, and 20Kg electronic scales, the weighing capacity is 20
A model weighing 10 kg requires an amplifier circuit with an amplification factor of 100 times, and a model weighing 10 kg requires an amplifier circuit with an amplification factor of 200 times.
The original required an amplifier circuit with an amplification factor of 400 times. As described above, in the past, an amplifier circuit was required for each weighing amount, and there was a demand for an improvement in this respect toward unification. <Purpose of the Invention> The present invention was made in response to these demands, and it is possible to improve the accuracy of the A/D converter without reducing its conversion accuracy, and without changing the amplifier circuit disposed before the A/D converter. An object of the present invention is to provide a new electronic scale that can be easily changed to various types of electronic scales with different weighing capacities, thereby reducing manufacturing costs. <Structure of the Invention> The present invention takes the following technical means to achieve the above object. That is, the first invention provides a weight sensor and a double integration type A/D converter that inputs an analog signal output from the sensor, integrates it, and outputs a digital signal according to the analog signal level. The electronic balance is configured to control the integration time of the analog signal in the A/D converter according to the weight of the scale by a software timer set in a program of a microcomputer. In addition, a second invention provides an electronic balance similar to the first invention, including a memory storing a plurality of different integration times, a selection means for selecting a desired one from the plurality of integration times, and a selection means for selecting a desired one from the plurality of integration times. and a soft timer that operates at a certain integration time, and the software timer is configured to control the integration time of the analog signal in the A/D converter according to the weight of the scale, and further A third invention is an electronic scale similar to the first invention, which is provided with a setting means for manually setting an integration time and a software timer that operates according to the set integration time. - A timer is configured to control the integration time of the analog signal in the A/D converter according to the weight of the scale. <Configuration of Examples> Examples of electronic scales of each invention will be described below based on the drawings. FIG. 1, FIG. 2, and FIG. 3 are block diagrams of respective embodiments of the first, second, and third inventions. Note that in these figures, the same reference numerals are used for the same parts, so the description of the same parts will be given only for one embodiment, and redundant description of each figure will be omitted. In these figures, A is a weight sensor consisting of a load cell, B is an amplifier circuit that amplifies the output signal of the sensor A, C1, C2, and C3 are double-integrating A/D converters, and D is the A/D converter. converter C
1, C2, C3 microcomputer [hereinafter
5a to 5c (referred to as CPU); E indicates unit price, unit quantity,
This is an input means for setting tare weight, etc. The above double integral type A/D converter C1, C2, C3
is an analog switch 1, an integrator 2, a comparator 3, a counter 4, and the CPUs 5a to 5c,
It is composed of the counter 4 and a clock oscillator 6 that drives the CPUs 5a to 5c. The analog switch 1 is configured to selectively input the reference voltage (Vref), amplifier output voltage (analog signal), and ground voltage to the integrator 2, and the switching control of the switch is as follows:
The switching is performed based on the switching command Sa from the CPUs 5a to 5c and the count stop signal Sb from the comparator 3. That is, when the count stop signal Sb is output from the comparator 3,
The contact point of analog switch 1 is switched to the c terminal, offset correction of integrator 2 is performed, and then
When the switching command Sa is outputted from the CPUs 5a to 5c, the contact point of the switch 1 is switched to the a terminal, and the integration of the analog signal is started.
Next, when the switching command Sa is output from the CPUs 5a to 5c, the contact point is switched to the b terminal, thereby switching from integration of the analog signal to inverse integration using the reference voltage (Vref). When the output voltage of the integrator 2 reaches the initial integration start voltage, the comparator 3 outputs a count stop signal Sb, which switches the above contact to the c terminal and outputs the next switching command Sa. Until this happens, offset correction of the integrator 2 is performed.
Such operations are repeatedly performed at regular intervals by software timers and instructions set in the CPUs 5a to 5c. When the output voltage of the integrator 2 reaches the initial integration start voltage, the comparator 3 switches between the analog switch 1 and the
It is configured to output a count stop signal Sb to the counter 4 and the CPUs 5a to 5c. The counter 4 is configured to be reset by a command Sc from the CPUs 5a to 5c output at the timing of starting inverse integration, to simultaneously start counting operation, and to stop the counting operation by a count stop signal Sb from the comparator 3. has been done. Each of the CPUs 5a to 5c receives the above switching command Sa.
The CPU 5a in FIG. 1 is equipped with a soft timer that outputs the timer at a predetermined timing, and the CPU 5a in FIG. 1 is equipped with a soft timer whose set time is fixed. ，
5c is equipped with a soft timer whose setting time is variable. In other words, A/D in Figure 2
The converter C2 includes a memory 7 that stores a plurality of different setting times, a selection means 8 for selecting a desired one from among the plurality of setting times, and a soft timer that operates at the selected setting time. The A/D converter C3 in FIG. 3 includes a setting means for setting the integration time of the analog signal. 9 and a soft timer operating at a set time thereof, the soft timer is configured to control the integration time of the analog signal. As a result, in the electronic scale shown in Fig. 1,
By changing the program constituting the soft timer, or in the electronic scales shown in Figures 2 and 3, by changing the set time of the soft timer, the desired count number of digital signals can be obtained. Obtainable. Therefore,
It is no longer necessary to change the amplification degree of the amplifier circuit B disposed before the A/D converters C1, C2, and C3, and the electronic scale can be used as is for various electronic scales with different weighing capacities. Become. For example, the output voltage when a 20kg object is loaded is
Weight sensor A designed to be 20 mv,
When manufacturing electronic scales with weighing capacities of 5Kg, 10Kg, and 20Kg using amplifier circuit B with an amplification factor of 100 times, the above can be achieved by setting the integration time of the analog signal as shown in the table below. A/D converter C
The maximum output counts of 1, C2, and C3 can be made the same for each scale.

[Table] Figure 4 shows the above A/
This is a time chart showing the relationship between each integration time and the output count number when the D converters C1, C2, and C3 are operated. In addition, the CPUs 5a to 5c in each of the above embodiments
In addition to the control operations for the analog switch 1, normal control operations for the scale are also carried out, but if necessary, a CPU dedicated to switching control of the analog switch 1 and a CPU for controlling the scale are installed.
A CPU can also be provided separately. Further, since the set time of the soft timer is given by the number of steps corresponding to the set time, a fixed number of steps is stored in the memory 7 as the set time. The selection means 8 is constituted by a suitable changeover switch, and in practice is used as a changeover switch for a measuring range. Further, the setting means 9 is composed of a digital switch, a numeric keypad, a depth switch, etc., and is also used as a span adjustment means.
In other words, span adjustment can be performed by matching the output count number of the A/D converter when a reference weight is loaded with the reference count number corresponding to the weight of the weight. By adjusting the integration time using the setting means 9 to match the count number, the span of the scale can be adjusted. FIG. 5 shows that in each of the above embodiments, the A/D
This figure shows another configuration in which the output counts of the converters C1, C2, and C3, that is, the resolution of the A/D converter can be freely increased. That is, 10 in FIG. 5 is a flip-flop that latches the overflow signal Sd of the counter 4.
When the overflow signal Sd is input to the set terminal S of the flip-flop 10, the Q output of the flip-flop 10 becomes H level, and when the CPUs 5a to 5c read this H level Q output, the corresponding counter 4 is configured to reset the flip-flop 10 by adding 1 to the number of overflows, and the CPU
5a to 5c are count stop signals of comparator 3.
When Sb is read, the number of overflows counted so far and the output count number Se of counter 4 are displayed.
The configuration is configured to calculate the total output count number from. As a result, the A/D converters C1, C2, C3 are not limited to the configuration of the counter 4.
The number of output counts can be increased, and the resolution can be freely increased accordingly. However, when reading the most significant digit of the counter 4 as the overflow signal, the flip-flop 10 can be omitted. <Operation of the embodiments> Next, the control operations of the CPUs 5a to 5c in each embodiment will be explained.The control operations of the CPU 5a shown in FIG. 1 are included in the control operations of the CPU 5b shown in FIG. Now, by explaining the control operation of the CPU 5b in FIG. 2, the explanation of the control operation of the CPU 5a described above will be replaced. FIG. 6 is a flowchart showing an example of the control operation of the CPU 5b shown in FIG.
Assume that the contact of analog switch 1 is connected to terminal c by . If you run the control program in this condition,
The CPU 5b checks the selection means 8 to determine the integration time designation mode (step-1), then sets the designation flag corresponding to it (step-2), and connects the contact of the analog switch 1 from the c terminal. Output command Sa to switch to terminal a (step-3). This starts the integration of the analog signal. Next, the CPU 5b monitors the integration time from the number of processing steps while executing other processing as a scale (arithmetic processing, key input processing, display processing, etc.).
When the integration time becomes equal to the integration time corresponding to the specified flag, in the next step 5, a command Sa is output to switch the contact of the analog switch 1 to the b terminal, and at the same time a command is issued to cause the counter 4 to reset and start. Output Sc. This completes the integration of the analog signal, and then the inverse integration using the reference voltage and the counting operation of the counter 4 are started. FIG. 7 shows an example of a detailed flowchart of step 4 in FIG. 6, in which a step counter is used to monitor the integration time from the number of processing steps. That is, first, the step counter is set to 0 (step-40), then the specified flag is determined (step-41), and the integration time corresponding to the specified flag is monitored. The number of stored steps corresponding to the integration time is compared with the count number of the step counter to determine if they match...Step 42]. As a result of the determination,
If the two do not match, increase the step counter.
1 [When inserting the process enclosed by the broken line, count a certain number of steps] and return to the process of step-41 again (step-43). As this loop process is repeated several times, the number of memorized steps and the step
When the count value of the counter matches, this loop is exited and the process proceeds to step-5 shown in FIG. When other processing is also performed during this loop, a fixed number of processing steps are executed between step-43 and step-41, as shown by the broken line. When the processing of step 5 is completed in this way, the CPU 5b checks the count stop signal Sb of the comparator 3 at regular intervals (step 5).
9), and executes a certain number of other processes in between the check processes (step-6). Also, as shown in Figure 5, the overflow signal of counter 4
When Sd is checked, the process shown by the broken line in FIG. 6 is executed between step-6 and step-9. That is, counter 4
Executes a certain number of other processing steps within a time shorter than the time it takes for outputting the overflow signal Sd (step-6), and when that is completed,
Check the Q output of flip-flop 10 (step-7). In this case, the Q output is L at the first time.
Since it is at the same level, step-8 is skipped and the process moves to check processing of the count stop signal Sb (step-9). As a result of the check,
If count stop signal Sb is at L level,
Returning again to the process of step-6, the same process is repeated. When the process of step 6 is completed, the Q output of flip-flop 10 is H.
Since the level has been changed, the next step is
8, the number of overflows is incremented by 1, and then a signal for resetting the flip-flop 10 is output. Further, as a result of checking the count stop signal Sb of the comparator 3 in step 9 above, if it is at L level, the same process as described above is repeated, and if it is at H level, inverse integration using the reference voltage is performed. Since the switching of the contact point to the c terminal has been completed, in the next step -10, the count value Se of the counter 4 is inputted and stored. Then, when the number of overflows is checked, the total output count is calculated from the number of overflows obtained in step-8 and the count value of counter 4 (step-11), and when the number of overflows is not checked, In this case, such processing is omitted, and after processing a certain number of steps in the subsequent steps, the process returns to the original step-1 again.
Return to , and repeat the above control operation. Note that the embodiment shown in FIG. 1 does not require changes in the integration time as described above, so from the control operation of the CPU in this case, the steps 1, 2, and
In addition, each process of step 41 and step 42 is omitted. FIG. 8 is a flowchart showing an example of the control operation of the CPU 5c in FIG. 3, and here only the parts that are different from FIG. 6 are shown. That is, in this case, in place of the processes in step 1 and step 2, a process (step 01) for converting the set time into a step number and storing this is newly inserted, and a process (step 01) is newly inserted in place of the processes in step 1 and step 2. The processing inserted between and step-5 is simplified as shown in the figure compared to that shown in FIG. <Effects of the Invention> As explained above, each of the inventions provides an electronic scale that includes a weight sensor and a double integration type A/D converter that converts the output analog signal into a digital signal. Since the integration time is controlled by a software timer set in the microcomputer program, the
Even without adjusting the input level to the D converter, a desired number of digital signals can be easily obtained by simply changing the set time of the soft timer. Therefore, it becomes possible to use an amplifier circuit with common specifications in various electronic scales having different weighing capacities, and the manufacturing cost thereof can be reduced. In addition, in the second and third inventions, software
Since the timer setting time can be easily changed, it is extremely easy to change the conversion speed and resolution of the A/D converter to match the specifications of the scale. The development cost of the /D converter can also be reduced. Furthermore, in the third aspect of the invention, the span of the scale can be directly adjusted by operating a setting means such as a digital switch, so that it is possible to omit the span adjustment circuit and the like that are conventionally required.
Therefore, the number of steps for manufacturing the amplifier board of the scale, etc. is reduced, and manufacturing costs can be reduced accordingly. Furthermore, since the span adjustment in the above invention is performed using a digital amount that is synchronized with the clock that drives the A/D converter, it is different from the conventional span adjustment that adjusts the input level (analog amount) of the A/D converter. , the adjustment operation becomes extremely simple and reliable. In addition, since the total output count of the A/D converter is calculated from the count of the counter of the A/D converter and the number of overflows of the counter, it is not limited by the number of output ports of the counter. Therefore, the resolution of the A/D converter can be freely increased as required.

[Brief explanation of drawings]

Figures 1, 2, and 3 are block diagrams of an embodiment according to the first, second, and third inventions, respectively, and Figure 4 shows the output count when the integration time of the analog signal is changed. FIG. 5 is a time chart showing the relationship between the number and integration time, FIG. In the embodiment shown in the figure
A flowchart showing an example of the control operation of the CPU 5b, FIG. 7 is a flowchart showing the detailed operation of step 4 shown in FIG. 6, and FIG. 8 is a flowchart showing the control operation of the CPU 5c in the embodiment shown in FIG. 3. This is a flowchart showing a part of the process. A...Weight sensor (load cell), C1, C2,
C3...Double integral type A/D converter, 5a, 5b,
5c...Microcomputer, 7...Memory,
8... Selection means, 9... Setting means.

Claims (1)

[Claims] 1. A weight sensor and a double integration type A/D converter that inputs an analog signal output from the sensor, integrates it, and outputs a digital signal according to the analog signal level. In the electronic scale equipped with
An electronic scale characterized in that the integration time of the analog signal in the A/D converter is controlled according to the weight of the scale by a software timer set by a program of a microcomputer. 2. An electronic scale comprising a weight sensor and a double integration type A/D converter that inputs an analog signal output from the sensor, integrates it, and outputs a digital signal according to the analog signal level. , a memory storing a plurality of different integration times;
A selection means for selecting a desired one from the plurality of integration times and a soft timer that operates at the selected integration time are provided, and the integration time of the analog signal in the A/D converter is determined by the soft timer. An electronic scale characterized in that the scale is controlled according to the weight of the scale. 3. An electronic scale comprising a weight sensor and a double integration type A/D converter that inputs an analog signal output from the sensor, integrates it, and outputs a digital signal according to the analog signal level. , there is a setting means for manually setting the integration time, and a software program that operates at the set integration time.
A timer is provided, and the software timer allows
An electronic scale characterized in that the integration time of the analog signal in the A/D converter is controlled according to the weight of the scale.