JPH034096B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement in a span adjustment circuit for an electronic scale.

<Prior Art> FIG. 1 shows an example of a span adjustment circuit in a conventional electronic scale.

In this figure, A is a weight sensor consisting of a load cell, B is an amplifier circuit that amplifies the output voltage of sensor A, R1 and R2 are voltage dividing resistors that divide the output voltage of amplifier circuit B, and C is a double integration type A. The /D converter Vr is a variable resistor whose input end is connected in parallel with the voltage dividing resistor R1, and whose output end is connected to the input end of the A/D converter.

The resistance value of this variable resistor Vr is selected to be much larger than that of the voltage dividing resistor R1, so that the change in resistance value of the variable resistor Vr is reduced in the combined resistance with the voltage dividing resistor R1. It is designed as follows. In addition, the reference voltage input terminal of the A/D converter C has a voltage (V1+V2) applied to the weight sensor A for tracking with the weight sensor A.
is appropriately divided by voltage dividing resistors R3, Rr, and R4 and inputted. The span of the scale is adjusted by operating the variable resistor Vr.

However, as is well known, the resistance value of the variable resistor Vr may change due to vibration, temperature change, aging, etc.
Even if the circuit configuration reduces the resistance value change of Vr,
Changes in resistance may change the span of the scale. In order to keep such a span change within an allowable range, the range that can be adjusted by the variable resistor Vr may be made small so that the influence of the resistance change of the variable resistor Vr can be ignored. However, since there are considerable variations in the rated output voltage of the weight sensor A, reducing the variable range of the variable resistor Vr may make it impossible to adjust the span of the scale.

For this reason, in the past, the reference voltage of the A/D converter C was adjusted in accordance with the output voltage of the weight sensor A, thereby keeping the span change of the scale within an allowable range.

However, such adjustment of the reference voltage requires the selection of voltage dividing resistors R3, Rr, and R4, and installation and replacement work by soldering, which results in extremely poor work efficiency and increases manufacturing costs. was.

<Object of the invention> This invention was made in view of such problems, and does not require adjustment of the partial pressure ratio as described above.
Therefore, it is an object of the present invention to provide an electronic scale that can eliminate the installation work by soldering and also allows the span adjustment operation to be extremely easy.

<Structure of the Invention> In order to achieve the above object, the present invention is characterized by the following structure.

That is, the primary integration time of the double integration type A/D converter that converts the weight signal into a digital value is controlled by a software timer, and the software
The operating time of the timer is changed in stages using a dip switch or the like, and variations in the output voltage of the weight sensor are adjusted using the dip switch. Fine adjustment of the span is performed using a variable resistor that varies the reference voltage or input voltage of the A/D converter. This results in
Variations in the output voltage of the weight sensor can be dealt with, and the variable range of the variable resistor can be made very small.

<Configuration of Embodiment> Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a block diagram showing the main parts of an embodiment of the present invention. In this figure, A is a weight sensor consisting of a load cell, B is an amplifier circuit that amplifies the output signal of the sensor A, and C1 is a discrete double integration type A/D converter.

This double integration type A/D converter C1 controls an analog switch 1, an integrator 2, a comparator 3, a counter 4, and the analog switch 1.
It consists of CPU5.

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 of the switch is controlled by the CPU.
5 and a 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 the analog switch 1 is switched to the c terminal, and the integrator 2
When the offset correction is performed and the switching command Sa is output from the CPU 5, the contact point of the switch 1 is switched to the a terminal, and the integration of the analog signal is started. When the next switching command Sa is output from the CPU 5, the contact point is switched to the b terminal, and the integration of the analog signal is switched to the 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 issues the next switching command.
Offset correction of the integrator 2 is performed until Sa is output.

The A/D converter C1 also includes a weight sensor A.
In order to track the voltage V1
A value obtained by appropriately dividing the voltage by voltage dividing resistors R5, R6, and R7 is input as the reference voltage Vref. Further, this reference voltage Vref is configured to be adjusted by a variable resistor Vr connected in parallel with the voltage dividing resistor R6. And a variable resistor
In order to keep the span change caused by a change in the resistance value of Vr within a permissible range, the resistance value of the variable resistor Vr is selected to be much larger than the resistance value of the voltage dividing resistor R6.

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
A count stop signal Sb is output to the counter 4 and the CPU 5.

Counter 4 is output at the same time as the inverse integration starts.
It is reset by a command Sc from the CPU 5 to start counting, and is stopped by a count stop signal Sb from the comparator 3. Further, this counter 4 is composed of a binary counter, but in order to enable counting exceeding its capacity, the CPU 5 counts this every time the counter 4 overflows, and the counter 4
When the counting operation is completed, the total output count number of the counter 4 is calculated from the output count number of the counter 4 at that time and the counted number of overflows. Then, the calculated total output count number is output as the output count number of the A/D converter C1 to a main CPU (not shown) that controls the entire scale.

Of course, it is also possible to control the entire scale by the CPU 5.

Further, this counter 4 is configured such that a count pulse Sd synchronized with one instruction cycle of a program set in the CPU 5 is supplied from the CPU 5.

The CPU 5 mainly controls the primary integration time of the A/D converter C1.
The CPU 5 is equipped with a soft timer that outputs the switching command Sa at a designated timing. The operating time of the timer can be adjusted by a switching means D that switches the operating time of the soft timer in stages.

The switching means D may be constituted by, for example, a dip switch or the like, and may be, for example, a
When it consists of a bit depth switch, it can be adjusted in 16 steps.

Also, the operating time of the soft timer is generally 1
Since the instruction cycle is given by the number of repetitions of a certain process (such as a knob process),
In the switching means D, the operation time corresponding to, for example, 250 instruction cycles can be adjusted by one stage of adjustment.

On the other hand, the counter 4 at this time is 1 as described above.
It is designed to count in synchronization with the instruction cycle. Therefore, for example, as shown in the operating characteristic diagram of the double integration type A/D converter in Fig. 3, the primary integration time T1 and the secondary integration time T2 when a weight equivalent to weighing is loaded are almost equal. In the case where the output count number of the A/D converter is adjusted by one step adjustment of the switching means D,
250 counts can be adjusted.

Therefore, in the span adjustment of this embodiment, the switching means D first performs coarse adjustment of the span, and the final fine adjustment is performed using the variable resistor Vr.
In other words, first adjust the zero point of the scale, then place a weight equivalent to the weighing amount on the weighing pan, and calculate the displayed value at that time (if the displayed value at no load is not 0, subtract that value A/
The switching means D and the variable resistor Vr are set so that the output value of the D converter or the value converted into a weight value) is equal to the weight of the weight (a certain number of counts for the weight of the weight or a value of the weight of the weight). You operate it to adjust the span of the scale.

Fine adjustment of the span can be done by changing the reference voltage with the variable resistor Vr.
In addition, this can also be done by adjusting the input voltage of the A/D converter C1 with a variable resistor.

<Operation of the embodiment> Next, the operation of the main part of the embodiment shown in FIG.
The explanation will be based on the flowchart shown in the figure.

In order to simplify the explanation, we will use the software here.
If the timer operating time is adjusted to approximately 10,000 steps, the output count number of the A/D converter when a weight equivalent to weighing is loaded becomes 10,000 counts, which corresponds to the weight of the weight. This will be explained using an example.

First, it is assumed that the contact of the analog switch 1 is connected to the c terminal at the initial time.

When the program is run in this state, the CPU 5 first reads the number of stages n set in the switching means D and presets this in the loop counter (step 1). Then, in the next step 2, a command Sa for switching the contact of the analog switch 1 from the c terminal to the a terminal is output. This starts the first-order integration for the unknown input voltage.

Next, the CPU 5 executes processing corresponding to approximately 8000 steps (step 3). This is a fixed operating time in contrast to the operating time of the soft timer which can be adjusted by the switching means D.

When the processing of step 3 is completed, next loop processing, which requires 250 steps in one loop processing, is repeated n times. That is, in step 4, approximately 248 steps of processing are executed, and in the next step 5, n is set to -1.
Then, in the following step 6, it is determined whether n is 0 or not. In this way, the above loop processing is repeated until n becomes 0, consuming 250 steps in one loop processing.

In this case, when n is set to 6, the total operating time of the soft timer is 8000+6×250=9500 steps. The output count number of the A/D converter at this time is that the input voltage of the A/D converter C when a weight equivalent to weighing is loaded is equal to the reference voltage, as shown in Figure 3. In that case, it would be almost 9500 counts. Therefore, in the span adjustment at this time, the number of steps set in the switching means D is 6 to 8.
By correcting this, the output count number of the A/D converter can be adjusted to approximately 10,000 counts. Adjustment in the area (1 to 249 count area) that cannot be adjusted with this switching means D is as follows:
This is done using a variable resistor Vr.

When the above loop processing is completed, a command Sa for switching the contact of the analog switch 1 to the b terminal is outputted, and a command Sc for prompting the counter 4 to reset and start is outputted (step 7). As a result, at the same time as the integration of the unknown input voltage is completed, the inverse integration using the reference voltage and the counting operation by the counter 4 are started.

When we enter this period of inverse integration (quadratic integration),
The CPU 5 checks whether the most significant bit (hereinafter referred to as MSB) of the counter 4 is high or low (hereinafter referred to as H or L) at a period shorter than a half period of the full count period of the counter 4, and thereby The number of overflows of the counter 4 mentioned above is counted. That is, first, in step 8, a process consisting of a fixed number of steps is executed to gain time, and in the next step 9, H and L of the MSB of the counter 4 are checked.
However, since the MSB is L during the half cycle of the full count period of the counter 4, the result of the check here is L. Therefore, initially, the flag is turned ON in the following step 10, and then the count stop signal of comparator 3 is turned on in step 11.
Check H and L of Sb. As a result of the check,
If it is H, the process moves to the next step 14, and if it is L, it returns to the original step 8. While repeating this loop process, half a cycle of the full count period of the counter 4 has passed, and the MSB changes from L to H.
When the screen changes to step 9, this time the steps start from step 9.
Move to 12.

In step 12, it is determined whether the flag is ON. At this time, it is initially ON, so
In the following step 13, the flag is turned OFF, the number of overflows is incremented by 1, and the process proceeds to step 11. Then, even if you return to step 8 and move from step 9 to step 12, the previous flag will be OFF at this time, so
During the half cycle when the MSB is H, the step 13
Pass and move to step 11 again.

In this way, the CPU 5 monitors the H and L levels of the count stop signal Sb of the comparator 3 while counting the number of overflows of the counter 4. Then, if the count stop signal Sb becomes H,
Since the inverse integration using the reference voltage and the switching of the contact point to the c terminal have been completed, the next step is
In step 14, the count number of the counter 4 is input, and the total output count number of the counter 4 is calculated from this and the counted number of overflows. Then, the calculated results are output to the main CPU.

Then, a process consisting of a fixed number of steps is executed, and time is spent to correct the offset of the integrator 2 (step 15), and then the process returns to step 1 again.

<Effects of the Invention> As explained above, the present invention includes a double integral type A/D converter that converts a weight signal into a digital value,
An electronic balance comprising a soft timer that controls the primary integration time of the A/D converter, a switching means that changes the operation time of the soft timer in stages to roughly adjust the span; /
Since it is equipped with a variable resistor that finely adjusts the span by continuously adjusting the reference voltage or input voltage of the D converter, variations in the output voltage of the weight sensor A can be adjusted by the switching means, Moreover, the switching can be performed using a deep switch or the like. Therefore, it is possible to omit the work of replacing the voltage dividing resistor and attaching the replaced voltage dividing resistor by soldering, etc., which were required in the past, and it is possible to improve the work efficiency and reduce the manufacturing cost. can.

Further, since the span can be coarsely adjusted using a dip switch or the like, the operation is extremely simple. Furthermore, the span of the scale can be adjusted using digital quantities instead of analog quantities.
The adjustment ratio that can increase the output value of the A/D converter by a predetermined number of counts can be easily grasped.
Therefore, anyone can easily, accurately, and quickly adjust the span without relying on experience or intuition.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of the main part of the span adjustment circuit in a conventional electronic scale, and Fig. 2 shows the
A block diagram showing an example of the main part of an embodiment of the present invention, FIG. 3 is an explanatory diagram for explaining the operating characteristics of a double integration type A/D converter, and FIG. It is a flowchart showing an example of the operation of the example. A...Weight sensor, B...Amplifier circuit, C1...
...Double integral type A/D converter, 5...CPU (with built-in soft timer), D...Switching means, Vr...
...variable resistor.

Claims (1)

[Claims] 1. In an electronic scale equipped with a double integration type A/D converter that converts a weight signal into a digital value and a soft timer that controls the primary integration time of the A/D converter, A switching means for coarsely adjusting the span by changing the operation time in stages, and a variable resistor for finely adjusting the span by continuously adjusting the reference voltage or input voltage of the A/D converter. An electronic scale characterized by: