JPH0569174B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) This invention is an improvement in a signal processing circuit for a weighing device that amplifies an analog weight signal and attenuates noise components caused by vibrations included in the signal. Regarding.

(Prior Art) In recent years, scales have been shifting from ones that weigh mechanically to ones that weigh using electronic devices.
In this way, weighing devices using electronic equipment amplify the analog signal output from the load cell, whose electrical resistance value changes depending on the load of the object to be weighed, using an amplifier circuit using an operational amplifier, and then use a filter to eliminate noise caused by vibration. After reducing the noise, the data is converted into a digital value by an analog-to-digital converter (hereinafter abbreviated as an A/D converter), and after arithmetic processing, this is displayed on a display device.

FIG. 6 is a block diagram of a signal processing section in a conventional combination weighing device composed of a plurality of weighing machines.

In the figure, a weight detector 1 such as a load cell is
A weighing hopper (not shown) is attached to output an analog weight signal proportional to the load to the amplifier circuit 2. A three-stage low-pass filter 3 ₁ , 3 ₂ , 3 ₃ is provided downstream of the amplifier circuit 2 to attenuate noise components such as vibration contained in the weight signal. 4 is a multiplexer that selectively outputs the weight signal of each weighing machine, 5 is a zero point adjustment circuit that cancels the voltage corresponding to the initial load of the weighing hopper, etc. included in the weight signal, and 6 is an adjustment of the zero point adjustment circuit 5. A control unit that controls the level, 7 is a sample and hold circuit, 8
9 is an A/D converter; 9 is a reference voltage control unit that controls the reference voltage of the A/D converter 8 for each weighing machine in order to maintain the span of each weighing machine at a predetermined value; 10
combines the weight values of each weighing machine to find the combination closest to the set target weight, and for the set of weighing machines found,
This is a computer that commands the discharge of objects to be weighed.

(Problems to be Solved by the Invention) Although high-speed processing is strongly required in such a combination weighing device, in the conventional mode, a response delay occurs due to the low-pass filter, so it is necessary to solve this problem. Therefore, there was a problem in that the metering speed could not be increased any faster than before.

That is, due to the opening and closing of the opening/closing gate of the weighing hopper attached to the weight detector, or the introduction of an object to be weighed into the hopper, a sudden load change occurs in the weight detector, and this effect causes a response to the low-pass filter. This remains as a delay, so it takes a considerable amount of time for the output value of the low-pass filter to become a weight signal proportional to the weight of the object being weighed, and as a result, the weighing speed cannot be made any faster. There was a problem.

Additionally, the applicant has filed Japanese Patent Application No. 60-5542,
-135437, etc., various inventions were disclosed in which failures in signal processing circuits were self-diagnosed to prevent measurement errors from occurring, but in particular, in combination weighing devices, etc., such self-diagnosis is not possible due to high-speed processing. Since the self-diagnosis operation must be performed between required metering operations, there was a demand that the self-diagnosis operation should also be processed at high speed.

The purpose of this invention is to solve the above-mentioned problems as a technical problem, and to improve the response delay without impairing the function of conventional low-pass filters, thereby increasing the weighing speed. It is an object of the present invention to provide an excellent signal processing circuit for a measuring device that is useful in the field of measuring technology by speeding up the self-diagnosis operation.

(Means and effects for solving the problem) In order to solve the above-mentioned problem, the present invention provides an initial stage amplification of the output signal of a weight detector equipped with an object loading means such as a weighing hopper. The weight signal is input to the circuit and amplified, and the amplified weight signal is input to an active filter that can be switched between a filter function and a buffer function to attenuate noise components contained in the weight signal.
Immediately before the weighing hopper is opened, the active filter is switched to the buffer function to isolate the capacitor constituting the filter from sudden voltage fluctuations caused by discharging and loading objects to be weighed. The voltage between the terminals of the capacitor is maintained at the voltage when the weighing hopper was loaded with the object to be weighed, and on the other hand, after the weighing hopper is closed and the object to be weighed is reinserted, the active filter is set to the filter function. By switching, the variation width of the voltage between the terminals of the capacitor when it functions as a filter is made small, thereby increasing the metering speed without impairing the attenuation characteristics of the active filter. In addition to providing a self-diagnosis circuit that outputs a constant voltage for testing in a self-diagnosis mode to self-diagnose the analog signal processing system up to the A/D converter,
A technical means is provided that speeds up self-diagnosis of an analog signal processing system by providing an operational amplifier circuit that adds and amplifies the weight signal output from the weight detector and the constant voltage output from the self-diagnosis circuit. This is what I learned.

(Embodiment - Configuration) Figures 1 and 2 show an embodiment of a combinational weighing device equipped with a signal processing circuit A according to the present invention. The computer 18 provided in each of the constituent weighing machines controls the signal processing circuit A of each weighing machine. The main computer 19 controls the signal processing circuit A of each weighing machine.

In these figures, a self-diagnosis circuit 12 for self-diagnosing the analog signal processing system up to the subsequent A/D converters 17A and 17B is installed at the output end of the weight detector 11 consisting of a load cell, etc. An operational amplifier circuit 13 that adds and amplifies the output voltage of the diagnostic circuit 12 and the output terminal voltage of the weight detector 11 is connected, and further downstream of the operational amplifier circuit 13,
Active filters 14 ₁ , 14 ₂ , 14 ₃ that can be switched between a filter function and a buffer function are connected. Further, each of the weight detectors 11 is attached with a weighing hopper (not shown).

FIG. 3 shows the self-diagnostic circuit 12, the operational amplifier circuit 13, and the active filters 14 ₁ , 14 ₂ , 14
3 shows an example of a more detailed circuit configuration such as No. ₃ .

In this figure, the self-diagnosis circuit 12 has the same configuration as that of the invention disclosed in the applicant's Japanese Patent Application No. 135437/1982, and in the weighing mode, a low level check signal SC is sent from the computer 18 to each switch SW1. , SW2, which closes switch SW1 and sets switch SW2 to open, thereby increasing the input voltage of self-diagnosis circuit 12.
A voltage equal to Vo is output from the adder circuit AD in the output stage, and in the self-diagnosis mode, switch SW1 is opened by switching the check signal SC to a high level.
SW2 is set to the closed state, and the adder circuit AD of its output stage outputs a value obtained by adding a constant voltage for inspection (a voltage proportional to the reference weight) to the input voltage Vo. .

The operational amplifier circuit 13 is composed of an operational amplifier whose input resistance is the bridge resistance of the load cell 11,
Moreover, at the inverting input terminal, the load cell 11
Current addition between the output of the self-diagnosis circuit 12 and the output of the self-diagnosis circuit 12 is performed. In the weighing mode, at the inverting input terminal of the operational amplifier circuit 13,
The output of the self-diagnosis circuit 12 and the output terminal voltage Vo of the load cell 11, which are substantially equal, are added together, and then differentially amplified by the operational amplifier circuit 13, from which the output terminal of the load cell 11 is output. Only the weight signal proportional to the input voltage is outputted, and in the self-diagnosis mode, the input voltage
The voltage obtained by adding a constant voltage to Vo is the self-diagnosis circuit 12
At the inverting input terminal of the operational amplifier circuit 13, this output voltage is added to the output terminal voltage of the load cell (the input voltage Vo), which is then differentially amplified by the operational amplifier circuit 13. The output terminal outputs a sum value obtained by adding a voltage corresponding to the weight weight generated by the self-diagnosis circuit 12 and amplified by the operational amplifier circuit 13 to a weight signal proportional to the output of the load cell 11. There is.

Each active filter 14 ₁ , 14 ₂ , 14 ₃ is
As shown in Figure 3, it has buffer amplifiers (voltage followers) OP ₁ , OP ₂ , OP ₃ and two input resistors connected in series to their non-inverting input terminals.
A capacitor C ₁ is interposed between the RC integrator circuits I ₁ , I ₂ , I ₃ and the midpoint of these two input resistances and the inverting input terminal of the buffer amplifiers OP ₁ , OP ₂ , OP ₃ .
A switch that opens and closes between C ₂ , C ₃ and the midpoint of the above two input resistances and the above capacitors C ₁ , C ₂ , C ₃
SW, the above non-inverting input terminal and the above RC integration circuit I ₁ ,
It consists of a switch SW that opens and closes between capacitors C ₁ ′, C ₂ ′, and C _{3 ′} of I ₂ and I 3, and the constants of these resistors and capacitors are determined by the filter 14 ₁ of the first stage. The second-stage filter 142 acts as a low-pass filter with a quick response and steep cut-off frequency characteristics, the second-stage filter ₁₄₂ acts as a low-pass filter with a slow response and slow cut-off frequency characteristics, and the third-stage filter ₁₄₃ acts as a low-pass filter with characteristics intermediate between these. They are each set to act as a low-pass filter with a Further, each switch SW is controlled to open or close by a control signal S output from the corresponding computer 18 or from the central main computer 19 for combinatorial calculation processing, and when this signal S is at a high level, each switch When SW is closed, each filter 14 ₁ , 14 ₂ , 14 ₃ acts as a filter function, and when this signal S is low level, each switch SW is opened and each filter 14 ₁ , 14 ₂ , 14 ₃ is configured to function as a buffer (voltage follower) with three stages in series.

Such active filters 14 ₁ , 14 ₂ ,
In the case shown in FIG. 1, the signal outputted via 14 ₃ is inputted to each double integral type A/D converter 17A via a zero point adjustment circuit 15 provided in each weighing machine. In the case shown in FIG. 2, the signal is input to the successive approximation type A/D converter 17B via the multiplexer 23, the zero point adjustment circuit 15 shared by each weighing machine, and the sample hold circuit 24.

As shown in FIG. 3, the zero point adjustment circuit 15 is composed of an operational amplifier, and at its inverting input terminal, the output of the third stage active filter ₁₄₃ and a D/A that controls the zero point adjustment level are connected. converter 16
The current is added to the output of the current. The double integral type A/D converter 17A in FIG.
The integration time is configured to be freely changeable using a software timer of the computer 18, and the span of the scale is adjusted by adjusting the integration time using the computer 18. Also the second
In the figure, the span adjustment of each weighing machine is performed by adjusting the reference voltage of the A/D converter 17B with the D/A converter 25.

The computer 18 in FIG.
The output value of the D converter 17A is read in a fixed cycle to determine whether a non-weighed object is loaded or unloaded, the stability of the weighing machine, etc., and the zero point adjustment and span adjustment are performed based on commands from the main computer 19, which will be described later. It is programmed to make adjustments, etc. Also,
The main computer 19 in FIG. 1 receives weight data from each computer 18, determines the combination closest to the set target weight based on this, and outputs the discharge pattern related to the determined combination to the computer 20.
It is designed to output to . computer 20
is adapted to control the timing of each weighing machine, feeder, etc., and output a drive command to the computer 21 of the weighing machine to be driven in accordance with the discharge pattern sent from the main computer 19. Further, the computer 21 provided in each weighing machine is programmed to directly control the drivers 22 of the pool hopper, weighing hopper, etc. upon receiving a drive command from the computer 20. Note that this computer 21 and the computer 18 may be constructed of the same computer.

On the other hand, the main computer 19 in FIG. 2 reads the weight data of each weighing machine, performs zero point adjustment,
It is designed to perform span adjustment, combination calculations, and drive control of each weighing machine. Of course,
These tasks may be appropriately divided among a plurality of computers as shown in FIG. Although an example of the basic circuit configuration has been shown above, a simple circuit configuration as shown in FIG. 4 can also be considered as the self-diagnosis circuit 12, and an amplifier circuit As 13, a high input impedance type differential amplifier as shown in FIG. 5 can also be used.

(Embodiment - Effect) In the above configuration, at the timing when a non-weighed object is put into the weighing hopper, the control signal S output from the computer 18 or the main computer 19 is held at a high level, and the active filter 14 ₁ , 14 ₂ , 14 ₃ switches SW
is set to the closed position. Then, the weight detector 11 of the weighing hopper into which the non-weighable object is loaded outputs a weight signal that is the sum of the initial load of the hopper and the weight of the non-weighable object. After this weight signal is amplified by the operational amplifier circuit 13, it is input to the active filters 14 ₁ , 14 ₂ , 14 ₃ and
Noise components caused by vibrations of the weighing hopper included in the weight signal are attenuated, and the signal is sent directly to the zero point adjustment circuit 15 or to the multiplexer 23.
The weight signal is inputted to the zero point adjustment circuit 15 via the zero point adjustment circuit 15, where the weight signal corresponding to the above-mentioned initial load is canceled. The output of the zero point adjustment circuit 15, which has become a voltage corresponding to the net weight of the object to be weighed, is as follows:
The A/D converters 17A and 17B convert the digital values into digital values, which are read into the computer 18 at predetermined timing and sent to the main computer 19.
or directly read into the main computer 19, where a combination calculation based on these weight data is performed. When the weighing machine related to the optimal combination is selected, the main computer 19 issues a drive command directly to the driver 22 of the corresponding weighing machine or indirectly to the driver 22 of the corresponding weighing machine via the computers 20 and 21. is transmitted, thereby starting the opening/closing operation of the weighing hoppers of the weighing machines selected as the optimal combination. On the other hand, immediately before or immediately after sending this drive command, each active filter 1 is sent from the computer 18 or the main computer 19.
A control signal S switched to low level is output to 4 ₁ , 14 ₂ , and 14 ₃ , and as a result, each filter 14 is switched on immediately before the opening/closing gate of the weighing hopper is opened.
The switches SW of ₁ , 14 ₂ , 14 ₃ are opened all at once, and the filters 14 ₁ , 14 ₂ , 14 ₃ of each stage are switched to the buffer function, and the capacitors C ₁ , 14 3 of each stage are switched to the buffer function.
The voltage between the terminals C ₂ , C ₃ , C ₁ ′, C ₂ ′, and C ₃ ′ is maintained at the value when the object to be weighed is loaded before the weighing hopper is opened.

Next, at the timing when the opening/closing gate of the weighing hopper is closed and the object to be weighed is reinjected from the upper pool hopper, or at the timing when the re-insertion of the object to be weighed is completed, the low level control signal S becomes high level. This causes each filter 14 to
Close the switches ₁ , 14 ₂ , and 14 ₃ all at once.
The filters 14 ₁ , 14 ₂ , 14 ₃ in each stage are switched to the filter function again. However, at this time, the voltage between the terminals of capacitors C ₁ , C ₂ , C ₃ , C ₁ ′, C ₂ ′, and C ₃ ′ in each stage is the value when the object to be weighed is loaded before the weighing hopper is opened. Therefore, when acting as a filter, the capacitors C ₁ , C ₂ , C ₃ , C ₁ ′,
The voltage fluctuations for C ₂ ′ and C ₃ ′ will be very small, so the step response until stabilization will be very short. Therefore, it is possible to shorten the time from when the object to be weighed is started being put into the weighing hopper until the weight data is read, and it is possible to improve the weighing speed by the amount of time that is shortened.

On the other hand, from the operational amplifier circuit 13 to the A/D converter 17
Self-diagnosis for the analog signal processing system up to A and 17B is programmed to be performed at appropriate intervals, and when the time for self-diagnosis comes, the selected object to be weighed is discharged. A weighing hopper to be self-diagnosed is selected from among the weighing hoppers, and the upper pool hopper corresponding to the selected weighing hopper is set to prohibit discharge. Then, as in the weighing mode, at the timing when the opening/closing gates of other weighing hoppers are closed and the objects to be weighed are re-injected from the upper pool hopper, or at the timing when the re-insertion of the objects to be weighed is completed, The control signal S held at low level is switched to high level, and in synchronization with this, or before and after this,
In the self-diagnosis circuit 12 of the weighing machine to be inspected,
A check signal SC switched to high level is output from the computer 18 or the main computer 19. As a result, switch SW2
is closed, switch SW1 is opened, and the self-diagnosis circuit 12 outputs a predetermined voltage for inspection.
This is added to the output terminal voltage Vo of the load cell 11 at the inverting input terminal of the operational amplifier circuit 13. As _a result, the operational amplifier circuit ₁₃ outputs a value obtained by adding the voltage corresponding to the weight weight to the _voltage corresponding to the initial load of the hopper. etc., the voltage is corrected to a voltage corresponding to the weight of the weight, further converted into a digital value by A/D converters 17A and 17B, and read into the computer 18 or main computer 19. The read value is then compared with the reference value corresponding to the weight weight, and if the difference is within a predetermined tolerance range, the analog signal processing system is determined to be normal; If the span is determined to be out of order, recovery measures are taken immediately. For example, in the case where the double integration type A/D converter 17A is used, the A/D converter 17A in the self-diagnosis mode
The integration time is adjusted by the computer 18 so that the output value of the converter 17A becomes equal to the reference value. In addition, the successive approximation type A/D converter 1
7B, the reference voltage is adjusted by the D/A converter 25 so that the output value of the A/D converter 17B is equal to the reference value.

Such self-diagnosis, or self-diagnosis and span adjustment, etc., is completed by the next cycle when the object to be weighed is put into the weighing hopper, and upon completion, the check signal SC, which was set to high level, is immediately switched to low level. , the self-diagnosis circuit 12 is
Switch to weighing mode. Also, during such self-diagnosis, the active filters 14 ₁ , 1
Since the switching control for 4 ₂ and 14 ₃ is performed, the step response when a constant voltage for testing is output from the self-diagnosis circuit 12 is also stabilized in a short time, which prevents an increase in the weighing speed. Appropriate self-diagnosis of the weighing machine can be performed between certain weighing cycles without having to do so.

It goes without saying that the embodiment of the present invention is not limited to the above-mentioned embodiment.
It is possible to adopt a configuration such as a stage, and
Even in the case of an active filter, various circuit configurations can be adopted depending on its characteristics. Furthermore, in addition to the combination weighing device, it is also applicable to automatic weighing devices that perform quantitative measurements.

(Effects of the Invention) As described above, according to the present invention, a switching means for switching the active filter, which causes the longest response delay in an analog signal processing system, between the filter function and the buffer function is provided, and the object to be weighed in the weighing hopper is When sudden load changes occur on the weight detector due to discharging, loading, etc., immediately before that happens, switch the active filter to the buffer function side to isolate the capacitors that make up the filter from voltage fluctuations caused by the load changes. As a result, the voltage between the terminals of the capacitor is maintained at the stable voltage value when the object to be weighed was loaded on the weighing hopper, the opening/closing gate of the weighing hopper is closed, and the object to be weighed is loaded again. or at the timing when the loading of the object to be weighed is completed, switch the active filter to the filter function side,
By attenuating noise components caused by hopper vibrations included in the weight signal, the range of voltage fluctuation of the capacitor that makes up the filter can be made extremely small, and the delay time of the step response can be minimized. can be made extremely short, and as a whole,
An excellent effect can be achieved in that the metering speed can be increased.

Furthermore, even in weighing devices equipped with a self-diagnosis circuit that outputs a predetermined voltage for testing analog signal processing circuits, self-diagnosis can be performed in a short time by controlling the switching of the active filter function described above. It is also possible to achieve the excellent effect that self-diagnosis can be performed on an appropriate weighing machine between certain weighing cycles without hindering the speed increase.

In addition, since the self-diagnosis can be performed in a short time, when a span error is detected by the self-diagnosis, it is possible to immediately adjust the span to correct it.

[Brief explanation of the drawing]

1 to 5 are explanatory diagrams of embodiments in which the present invention is applied to a combination weighing device, and FIG. 1 is a circuit diagram of the combination weighing device when each weighing machine is equipped with an A/D converter. A block diagram of the configuration; Figure 2 is a block diagram of the main parts of a combination weighing device in which the measured values of each weighing machine are digitally converted by one A/D converter; FIG. 4 is a circuit diagram showing an example of an analog signal processing system, FIG. 4 is a circuit diagram showing another embodiment of the self-diagnosis circuit, FIG. 5 is a circuit diagram showing another embodiment of the operational amplifier circuit, and FIG. 6 is a circuit diagram showing another embodiment of the operational amplifier circuit. FIG. 2 is a block diagram showing the main parts of a conventional combination weighing device. 11... Weight detector, 12... Self-diagnosis circuit,
13...Amplification circuit (operational amplifier circuit), 14 ₁ , 14
_{2,14 3} ...Active filter, SW...Switching means, A...Signal processing circuit.

Claims (1)

[Scope of Claims] 1. An amplifier circuit that amplifies a weight signal output from a weight detector, an active filter that is connected to the subsequent stage and attenuates noise components included in the weight signal, and that has a filter function and a buffer function. 1. A signal processing circuit for a weighing device, comprising: a switching means for switching between functions; 2. The signal processing circuit for a weighing device according to claim 1, wherein the active filter comprises a plurality of stages. 3. Claim 1, wherein the active filter is a low-pass filter.
A signal processing circuit for a measuring device according to item 1 or 2. 4. The signal processing circuit for a weighing device according to claim 1, wherein the weight detector is provided with a weighing hopper. 5. The signal processing circuit for a weighing device according to claim 4, wherein the switching means is set to the buffer function side when discharging and loading objects to be weighed in the weighing hopper. 6. A self-diagnosis circuit that outputs a constant voltage in self-diagnosis mode to self-diagnose the analog signal processing system, and adds and amplifies the weight signal output from the weight detector and the constant voltage output from the self-diagnosis circuit. A weighing device comprising: an operational amplifier circuit; an active filter connected to the subsequent stage to attenuate noise components contained in a weight signal; and switching means for switching the filter between a filter function and a buffer function. signal processing circuit. 7 The self-diagnosis circuit inputs the output voltage of the weight detector, outputs a voltage equal to the input voltage in the weighing mode, and outputs a voltage equal to the input voltage in the self-diagnosis mode by adding a constant voltage for testing to the input voltage. 7. The signal processing circuit for a measuring device according to claim 6, wherein the signal processing circuit is configured to output a signal. 8. The signal processing circuit for a weighing device according to claim 6, wherein the active filter comprises a plurality of stages. 9 Claim 6, wherein the active filter is a low-pass filter.
9. A signal processing circuit for a measuring device according to item 8. 10. The signal processing circuit for a weighing device according to claim 6, wherein the weight detector is provided with a weighing hopper. 11 Discharge of the object to be weighed from the weighing hopper,
Claim 10, characterized in that the switching means is set to the buffer function side when the switch is turned on.
A signal processing circuit for the measuring device described in Section 1. 12. The signal processing circuit for a weighing device according to claim 10, wherein the self-diagnosis circuit is set to a self-diagnosis mode when the weighing hopper is empty.