JPS6355403A - Calibrating device for strain measuring device - Google Patents

Abstract

PURPOSE:To always generate an exact calibration value voltage by providing a calibration value generating circuit for generating a calibration value voltage which has been corrected. CONSTITUTION:A calibration value generating circuit 6 generates a calibration value voltage being equal to a voltage corresponding to a prescribed strain amount outputted from a measuring bridge. Also, in a resistance value setting circuit 7, when a resistance value of a strain gauge is different from a reference resistance value, the resistance value of the strain gauge is set numerically, and a setting signal corresponding to the set resistance value is outputted. Subsequently, in a correction value generating circuit 8, a ratio of the resistance value which has been set by the setting signal of the resistance value setting circuit 7, and the reference resistance value is multiplied by the calibration value voltage of the circuit 6, and a corrected calibration value voltage is generated. Next, a gain setting circuit 3 receives selectively the corrected calibration value voltage and an output of the measuring bridge by an operation changeover switch 9, outputs the calibration value voltage by adjusting it to a prescribed level by a gain which is set by an eternal operation, and outputs it, and also, receives an output of the measuring bridge. In this way, a measuring output related to the corrected calibration value voltage is obtained.

Description

Detailed Description of the Invention (a) Technical Field The present invention relates to a calibration device for a strain measuring instrument, and more specifically, it applies a constant current from a bridge power supply to a measurement bridge consisting of a resistance bridge using a strain gauge, and performs the measurement. The present invention relates to a calibration device for a strain measuring instrument that amplifies the output obtained from a bridge and obtains a measurement output.

(b) Prior Art Generally, in a strain measuring instrument, a Wheatstone bridge including a strain gauge on at least one side is connected to the input side in order to convert the amount of strain into an amount of electricity. As shown in FIG. 5, when the bridge power supply 62 that applies voltage E is connected to the input terminals 61 and 61' of the Wheatstone bridge 60 whose input resistance and output resistance are both Rg, Bridge output voltage E
The relationship between O and the bridge input voltage Ei between the input terminals 61 and 61' will be explained.

Note that 64.64' is the wire resistance of the connection cable from the bridge power supply 62 to the bridge input terminal 61.61', and r is the resistance value thereof.

There are two ways to drive the Wheatstone bridge. One is a constant voltage drive method, and the other is a constant current drive method.

First, in the case of the constant voltage drive method, the relationship between the bridge input voltage Ei and the bridge output voltage Eo is as shown in equation (1).

Ei = (Rg / (Rg +2 r)) ・E-
(1) Therefore, when the connection cable is long, the line resistance r increases and this difference occurs. Furthermore, if a remote sensing method is used to eliminate this difference, separate wiring for remote sensing is required, and the distance from the bridge power supply 62 to the bridge input terminal 61°61' is long (100°
0 m), the wiring for remote sensing is not only uneconomical, but also the workability of installation, wiring, etc. is reduced.

On the other hand, in the case of a constant current drive method, the bridge input voltage E
i has the relationship of equation (2).

Ei = I・Rg ・・・・・・
(2) In this case, since the power supply current is constant, the wire resistance r
become unaffected by However, as can be seen from equation (2), if the bridge resistance Rg changes, that is, if the strain gauge is replaced with a strain gauge having a different resistance (nominal gauge resistance) in actual measurement, the input voltage Ei changes. in general,
When the bridge circuit shown in FIG. 5 is composed of strain gauges, equation (3) holds true.

Eo=K·ε·Ei /4 -- (3) However, in the above equation (3), K is the gauge factor and ε is the strain. Therefore, the bridge output voltage Eo, which is the measured value, should originally be a function only of the strain ε;
Since the bridge input voltage Ei is added as a variable, accurate measurements cannot be made, or only a strain gauge with one type of gauge resistance can be used.

Therefore, a calibration value corrected with multiple gauge resistances, for example, a calibration value of 2000 μs, 1000 μs, corrected to fit a Wheatstone bridge configured with a strain gauge with a nominal gauge resistance of 120 Ω and 350 Ω, respectively.
. 68 injection calibration devices have already been considered. That is, in this calibration device, the calibration value voltage from the calibration value generation circuit 65 is injected into the gain 11 adjustment circuit 68, and the gain of the amplifier 68b is adjusted by the externally operable variable resistor 68a. The reference position (reference value) can be set by aligning the 69 pointer with the full scale position or a predetermined scale line. In the calibration device of FIG. 5 configured in this manner, for example, a load transducer is constructed in which a Wheatstone bridge 60 is assembled with a strain gauge having a gauge resistance of 120Ω, and the rated capacity Lot is 185Ω.
A case will be described in which a load transducer that generates a strain of 0 με (με: 10−11 strain) is calibrated.

First, among the calibration values that can be generated by the calibration value generation circuit 65, the value closest to the above distortion amount of 1850μE, for example 2000μE, is selected.
ε (the selection mechanism is not shown). Then,
The calibration value generation circuit 65 outputs a calibration value voltage (generally 1
με=1 μV) is output and injected into the gain adjustment circuit 68. The calibration value 2000με output from this calibration value generation circuit 65 and the rated strain of the load converter 1850μ
Since there is a deviation from ε, the load corresponding to 2000 με is calculated using the following equation (4).

(2000/1850)X10+10.8(t)...
...(4) This 2000με calibration value output (voltage or waveform) is
The measurement output is calibrated as 0.8t. That is, by adjusting the variable resistor 68a, the pointer of the meter 69 is set to 10.8t.
Align with the scale.

Next, when the calibration operation switch 67 is turned OFF and the load to be measured is applied to the load converter, the bridge output voltage EO at that time is inputted to the gain adjustment circuit 68 via the buffer amplifier a70 and sent to the meter 69. Is displayed.

However, with the above calibration device, the calibration values can only be corrected for nominal gauge resistances of 120Ω and 350Ω. Among the gauge resistors commonly used today (in addition to the 120Ω and 350Ω mentioned above, 500Ω and 1000Ω
etc., and in reality, multiple converters (bridge circuits 60) are often connected in parallel, and if we consider the gauge resistances synthesized in this way, there are an infinite number of gauge resistances. Therefore, it is practically impossible to generate calibration values for such a variety of gauge resistances.

On the other hand, it is ideal that the calibration values that can be calibrated as a strain measurement device can be set continuously, but in reality, the calibration values can be set continuously.
some multiplier-related limited calibration value, e.g. 2000μ
ε, 1000με.

The configuration is such that 500με, 100με, 50με, etc. are generated in stages. Therefore, even if we limit the nominal gauge resistance to four types: 120Ω, 350Ω, 500Ω, and 1000Ω, and limit the calibration values to the five types from 2000με to 50με, the calibration values for each of the above-mentioned nominal gauge resistances will differ. To correct this, there will be 4×5=20 combinations (including overlapping combinations). moreover,
If an attempt is made to create a configuration that can also be corrected using the synthesized nominal gauge resistance as described above, the number of parts will increase to an unrealistic number, resulting in a large bulk, making it almost impractical.

(c) Purpose The present invention was made in view of the above-mentioned circumstances, and its purpose is to provide a simple circuit configuration, regardless of the value of the gauge resistance of the strain gauge assembled in the measurement bridge. It is an object of the present invention to provide a calibration device for a strain measuring instrument that can always generate an accurate calibration value voltage, is extremely easy to operate, and can enjoy all the advantages of a constant current drive system.

(d) Structure In order to achieve the above object, the present invention applies a constant current from a bridge power supply to a measurement bridge consisting of a resistance bridge using a strain gauge, amplifies the output obtained from the measurement bridge, and obtains a measurement output. In a strain measuring instrument, a calibration value generation circuit that generates a calibration value voltage equal to a voltage corresponding to a predetermined amount of strain output from a measurement bridge composed of a strain gauge having a certain reference resistance value, and the measurement bridge described above. A resistance value setting circuit that can numerically set the resistance value of the strain gauge when the resistance value of the strain gauge that constitutes the strain gauge is different from the reference resistance value, and outputs a setting signal corresponding to the numerically set resistance value. A circuit is inserted into the input or output side of the calibration value generation circuit, and the ratio of the resistance value set by the setting signal of the resistance value setting circuit to the reference resistance value is calculated by the calibration value generation circuit. A correction value generation circuit that multiplies the calibration value voltage to generate a corrected calibration value voltage, selectively receives the corrected calibration value voltage and the output of the measurement bridge, and outputs the corrected calibration value voltage to an external circuit. It is configured with a gain setting circuit that adjusts and outputs a predetermined level according to a gain set by operation, and also receives the output of the measurement bridge and outputs a measurement output related to the corrected calibration value voltage. be.

Hereinafter, the gist of the present invention will be explained in detail based on examples.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a calibration device for a strain measuring instrument according to the present invention, and FIG. 2 is a circuit diagram showing a circuit configuration of the same embodiment.

In FIG. 1, 1 is a Wheatstone bridge circuit configured to include a strain gauge on at least one side, that is, a measurement bridge, and converts a load transducer, pressure transducer, displacement transducer, etc. that converts a physical quantity into an electrical quantity. part, 2
63 is a buffer amplifier circuit with an amplification degree of rlJ, which receives the electrical quantity from the converter 1 and is made of a porticivorowa or the like. 63 receives the output of the buffer amplifier circuit 2, and has a gain by a variable gain amplifier whose gain can be set externally using a variable resistor or the like. This is a setting circuit, and 4 is a display circuit such as a meter that displays the output of the gain setting circuit 3 in analog form. 5 is a reference voltage generation circuit that maintains a constant voltage, and 6 is a calibration value generation circuit that divides the output voltage of this reference voltage generation circuit to generate a predetermined calibration value. 7 is a resistance value setting circuit configured using three digital switches each having a 4-bit BCD output, and 8 is a resistance value setting circuit 7 that uses the output voltage of the calibration value generation circuit 6. This is a correction value generation circuit that generates a corrected calibration value voltage by multiplying the above calibration value voltage by a coefficient between the resistance value set in and a certain reference resistance value to be described later. Reference numeral 9 designates an operation changeover switch using a transfer contact, 9a is a normally open contact, 9b is a normally closed contact, and 9c is a common contact.

In other words, when the normally open contact 9a is closed (when it is turned to the side indicated by the letters CAL), the calibration operation is activated, and when the normally closed contact 9b is closed (when it is pushed to the side indicated by the letters MEAS), the calibration operation is activated. When the device is tilted to the opposite side), it is configured to perform a measurement operation.

On the other hand, 10 is a current detection circuit that detects the supplied current for driving the Wheatstone bridge circuit of the conversion section 1, and 11 is a current detection circuit that compares the output of this current detection circuit 10 with the output of the reference voltage generation circuit 5. 12 is a current control circuit that maintains the drive current supplied to the converter 1 constant based on the control signal from this comparison circuit; 13 is a current control circuit of this current control circuit 12; It is an unregulated power supply that is subject to control. Note that the reference voltage generation circuit 5, the current detection circuit 1o, the comparison circuit 11, and the current control circuit 1
2 and the unregulated power supply 13 constitute a constant current source 14. Therefore, the bridge power supply method to the measurement bridge is a constant current drive method. Further, the reference voltage generation circuit 5 is shared by the calibration value generation circuit 6 and the comparison circuit 11.

In FIG. 2, reference numeral 15 includes a strain gauge with a nominal gauge resistance Rg on at least one side, and a Wheatstone bridge circuit (hereinafter referred to as a "bridge circuit") as a measurement bridge in which input resistance and output resistance both have approximately the same resistance value Rg.
16.16' is a bridge input terminal connected to the constant current source 14 as a bridge power supply,
7.17' is a bridge output terminal.

Note that the voltage between the bridge input terminals 16 and 16' is hereinafter referred to as the bridge input voltage and expressed as Ei, and the voltage between the bridge output terminals 1 and 16' is referred to as the bridge input voltage.
The voltage between 7 and 17' is called the bridge output voltage and is expressed as Eo.

18 is a voltage follower having a sufficiently large input impedance compared to the bridge output resistance Rg so as not to cause disturbance to the bridge circuit 15;
It outputs 1 μV to the ε strain, and its input terminals are connected to bridge output terminals 17 and 17', respectively.

19 is an operational amplifier, the non-inverting input terminal of which is grounded. 20 and 20' are input resistors both having the same resistance value Ri, one end of which is connected in common to the inverting input end of the operational amplifier 19, and the other end of the input resistor 20 is connected to the output end of the voltage follower 18. The other end of the input resistor 20' is connected to the common contact 9c of the operation changeover switch 9.

21 is a feedback resistor consisting of a variable resistor, and operational amplifier 19
is connected between the inverting input terminal and output terminal of. In addition, the input resistor 20, 20', the feedback resistor 21 and the operational amplifier 1
9 constitutes an inverting and summing amplifier, and this circuit portion will hereinafter be referred to as gain setting circuit 3. Reference numeral 22 denotes a meter as the indicator 4, one end of which is connected to the output end of the gain setting circuit 3, and the other end of which is grounded.

When the output of this gain setting circuit 3 is 1V, full scale is indicated. On the other hand, 23 is a reference power source as the reference voltage generating circuit 5, the negative terminal of which is grounded, and its output voltage is expressed as Es. 24 to 29 are voltage dividing resistors for generating calibration values, and their respective resistance values are represented by r1 to r6. 30 is a calibration value selection switch consisting of an externally operable rotary switch, and 30a to 30e each have a 2000μ
E contact, 1000μE contact, 500με contact, 100μ
They are an ε contact and a 50 με contact, and 30f is a common contact. One end of the voltage dividing resistor 24 is connected to the positive end of the reference voltage 23, and the other end is grounded via voltage dividing resistors 25 to 29 connected in series. In addition, 2000μE contact 30a
are connected to the connection point of the voltage dividing resistors 24 and 25, and similarly, the 1000με contacts 30b to 50με contacts 30e are connected to the voltage dividing resistors 25 and 26, the voltage dividing resistors 26 and 27, the voltage dividing resistors 27 and 28, and the voltage dividing resistors 27 and 28, respectively. It is connected to the connection point between piezoresistors 28 and 29. In addition, the circuit part (the part surrounded by the broken line in the figure) consisting of the voltage dividing resistors 24 to 29 and the calibration value selection switch 30
constitutes a calibration value generation circuit 6. Also, 2000μ
The output voltage of each of the E contact to the 50με contact is 1 to
■Resistance value r1 of voltage dividing resistors 24 to 29 when expressed as 5
The relationship with ~r6 is configured as shown in equation (5) below.

rV1= ((r2+rs +ra +rs +rs)
/ro) ・Es =2000μV V2== ((re +r4+rs 10rs)/ro'
t・Es=1000μv Vs = ((r+ +rs +rs)/re)・
Es=500μv V4=((rs+rs)/re) ・Es=100μ
V V5= (rs/re) #Es =50ttVJ・
...(5) However, ro ==rt +r2+rx +r4+r5
+rs The common contact 3Of is connected to the input end of the correction value generation circuit 8, and the output end of the correction value generation circuit 8 is connected to the normally open contact (CAL side contact) of the operation changeover switch 9.

31 to 33 are resistance value control output signals as setting signals consisting of 4 bits for each digit of the resistance value setting circuit 7;
1 is the resistance value control output signal for the least significant digit, and 33 is the resistance value control output signal for the most significant digit.

FIG. 3 is a circuit diagram showing a specific embodiment of the correction value generation circuit 8, which is the main part of the present invention.

In the figure, 34 is a calibration value input terminal, which is connected to the common contact 30f of the calibration value generation circuit 6.

35a-35e, 36a-36e and 37a-37e
are analog switches, I is an input terminal, 0 is an output terminal, and C is a control input terminal. In this analog switch, when the control input terminal C becomes H level, the input terminal I and the output terminal 0 are connected, and when the control input terminal C becomes L level, the analog switch becomes open. 38a-38e, 39a-39o and 4
0a to 40e are input resistors, respectively, and their respective resistance values are input resistors 38a and 38b.

38c38d are 8Ω, 4Ω, 2Ω, and lΩ, respectively, and these resistance values are the input resistances 39a to 39d, 40a to
The same applies to 40d.

The resistance values of the input resistors 38e, 39e, and 40e are as follows:
They are 800Ω, 80Ω, and 8Ω, respectively.

41a to 41c and 42 are operational amplifiers, each having a non-inverting input terminal grounded to form an inverting amplifier. 438-43c are operational amplifiers 41a-41c, respectively.
A feedback resistor is connected between the inverting input terminal and the output terminal of the circuit, and the respective resistance values are 800Ω, 80Ω, and 8Ω.

The input resistors 38a to 38e have one end commonly connected to the inverting input terminal of the operational amplifier 41a, and the other end to the output terminal 0 of the analog switches 35a to 35e, respectively. The analog switches 35a to 35e, 36a to 36e and 37a to 3
The input terminals I of 7e are connected in common to the calibration value input terminal 34. Also, as above, the output terminals of the analog switches 36a to 36e and 37a to 37e
have input resistors 39a to 39e and 40a to 40a, respectively.
One end of 40e is connected in series, and the other end is connected in common to the inverting input terminal of operational amplifiers 41b and 41c, respectively. 45 is a feedback resistor with a resistance value R connected between the inverting input terminal and the output terminal of the operational amplifier 42, and 46a to 46c are input resistors with a resistance value R, one end of which is connected to the output terminal of each of the operational amplifiers 41a to 41c. The other ends are connected in common and connected to the inverting input end of the operational amplifier 42. 47 is the output terminal of the correction value generation circuit 8, which is connected to the normally open contact (CAL side contact) 9a of the operation changeover switch 9.6The output terminal of the operational amplifier 42 is the output terminal of the correction value generation circuit 8. It is connected to terminal 47.

On the other hand, 488 to 48c are negative logic input AND gates having four input terminals, each output terminal being connected to the control input terminal C of the analog switches 35e, 36e and 37e.

49a to 49d, 50a to 50d and 51a
~51d are 4-bit BCD signals, which are connected one-to-one to the control input terminals C of the analog switches 35a-35d, 36a-36d, and 37a-37d, and are connected to the respective control input terminals C of the negative logic input AND gates 48a-48c. It is connected one-to-one with the input terminal. Furthermore, 49a.

50a and 51a are the least significant bits (LSB), respectively, and 49d, 50d, and 51d are the most significant bits (MSB), respectively.

52 is a digital switch consisting of three digits as the resistance value setting circuit 7, B1 to B3 correspond to the resistance value control output signals 31 to 33, respectively, B1 is the first 4-bit BCD output terminal, B2 . B3 is a 4-bit BCD output terminal for the 10th and 100th positions, B is a power input terminal for generating signals and is supplied with +5V, and G is a common contact terminal, which is grounded. Further, 53a to 53c are knobs for numerically setting the 1st, 10th, and 100th positions of the resistance value, respectively.
It can be set up to 9, and 54a to 54c are display windows that display the numerical values 0 to 9 set by the setting knobs for each digit.

FIG. 4 is a circuit diagram showing the basic configuration of the constant current source 14.

In the same figure, 55 is the current detection circuit 10 in FIG.
56 is an error amplifier as comparator circuit 11, 57 is a control transistor as current control circuit 12, 58° 58' is a constant current output terminal as a bridge power supply, and 56 is an error amplifier as comparator circuit 11. 16 and 16', respectively. One end of the current detection resistor 55 is connected to the output terminal 58 and the inverting input terminal of the error amplifier 56, and the other end is grounded and connected to the negative electrode side of the unregulated power supply 13. The non-inverting input terminal of the error amplifier 56 is connected to the positive end of the reference power supply 23 as the reference voltage generating circuit 5, and the output terminal of the error amplifier 56 is connected to the base of the control transistor 57.
The collector of this control transistor 57 is connected to the unregulated power supply 1.
The emitter is connected to the output terminal 58'.

Next, the operation of this embodiment configured as described above will be explained. For convenience of explanation, the operation of the constant current source 14 as a bridge power supply shown in FIG. 4 will be explained first.

If the voltage generated when the supplied current from the unregulated power supply 13 flows through the current detection resistor 55 is Er, the error amplifier 56 compares this voltage Er with the output voltage Es of the reference power supply 23, and the error amplifier 56 compares this voltage Er with the output voltage Es of the reference power supply 23 and When Er is small, the base potential of the control transistor 57 is raised to increase the supply current, and conversely, when Er is larger than Es, the base potential of the control transistor 57 is increased.
By lowering the base potential of 7, the supplied current is lowered, and as a result, a constant current is supplied.

Next, the operation of the entire embodiment except for the constant current source 14 will be explained.

Now, if the sensor connected as the input of the strain measuring device is a load transducer with a rated capacity Lot and a rated strain of 1850με, and the strain gauge forming the bridge circuit 15 has a nominal gauge resistance of 508Ω. This will be explained using an example. First, as an operation for calibration, the calibration value closest to the rated strain 1850 με is selected using the calibration value selection switch 30 (FIG. 2). In other words,
In this case, turn the selection switch 30 to select 2000με contact 3.
Connect the common contact 30f to 0a. Next, the first digit setting knob 53a of the digital switch 52 (FIG. 3) is turned so that the display window 54a displays "8". Similarly, the display window 54b for the 10th digit shows job and 1.
Set the setting knob 53b so that the display window 54c for the 00th digit shows "5".

Turn 53c. Furthermore, turn the operation changeover switch 9 to the CAL side. In this example, the calibration value input terminal 34 (Fig. 3)
The voltage input to is 2000με, which corresponds to 2000με assuming that the resistance value of the gauge resistance (reference resistance) of the strain gauge that makes up the measurement bridge is 1Ω.
A voltage of μV is applied. Then, the BCD corresponding to the digital switch number "8" is 100, and the BCD corresponding to the decimal number "0" is 100 from the 10th digit CD output terminal B2.
The BCD corresponding to the decimal number "5" is output from the digit BCD output terminal B3. In other words, the first digit BC
The D output signals 51a to 51C are at L level, the BCD output signal 51d is at H level, and the 10th digit BCD output signal 50
A to 50d are all L level.

Also, of the 100th digit BCD output signal, 49a is H level, 49b is L level, 49c is H level, and 49d is L level.
level. Therefore, in the circuit for the 100th digit, the analog switches 35a+35c are turned on and the input resistor 3
8a and 380 become effective as input resistances of the operational amplifier 41a. The combined input resistance is 16/10Ω, and the feedback resistor 43a is 800Ω, so the operational amplifier 41a operates as an inverting amplifier with an amplification factor of 500 times. Furthermore, in the 10th digit circuit, the analog switches 36a to 36d are inactive, and the negative logic input AND
The output of the gate 48b becomes H level, only the analog switch 36e is turned on, the inverting input terminal of the operational amplifier 41b is grounded via the input resistor 39e, and its output becomes O
hold v. Next, in the first digit circuit, only the analog switch 37d is turned on, and only the input resistance 40d becomes effective as the input resistance of the operational amplifier 41c.

Therefore, the operational amplifier 41c operates as an inverting amplifier with an amplification factor of 8 times. Expressing these results numerically,
The output voltage of the operational amplifier 41a is 2000 (μV)
500=1 (V).

The output voltage of the operational amplifier 41c is 2000 (μv) x
8=o, o 16 (V), which are added by the summing amplifier consisting of the operational amplifier 42, 1+0°016 = 1
．． 016 V, and an output voltage of 1.016 V is output from the output terminal 47 by correcting the calibration value of 2000 με with the nominal gauge resistance of 503 Ω.

Now, if the nominal gauge resistance and the bridge resistance are equal to Rg (generally, the bridge is configured in this way),
Since the bridge input voltage Ei is driven by a constant current, if the constant beach supply current is represented by ■, the formula (6) is obtained.

Ei=I・RR・・・・・・(6) Eo=K・ε−I −Rg /4 ・−C7)
Furthermore, by substituting the above equation (6) into equation (3) shown in the prior art section, equation (7) is obtained.

Therefore, assuming an arbitrary amplification system with a gain of G and an output of Et, and when the EO shown in the above equation (7) is input to this amplification system, the input-output relationship is the equation (8) and (8). )2
The formula becomes

Et = G-Eo - (8
)Et=G-K・ε・engine・Rg/4 ・・・・・・(
8)' Then, the output EC of the correction value generation circuit is the constant current I
Assuming that the reference resistance value Rs of the strain gauge of the bridge circuit 15 receiving the voltage is 1Ω, Ec = ε・Rg /
Since it can be expressed as Rs = ε・Rg −-(9),
The following equation (10) is obtained from equation (8) 2.

Et = G −K ・I ・Ec
--00) From this, the output of the gain setting circuit 3 is Et
Then, the gain setting circuit 3 is realized as an amplifier having a gain G in equation (10).

By the way, the corrected calibration value 2000 με output from the correction value generation circuit 8 and the rated strain 1850 of the load converter
Since it deviates from με, 200
The load corresponding to 0 με is calculated using the following equation (11).

(2000/1850)xlO=10.8 (t)・
(11) Calibrate the measurement output by setting this 2000με calibration value output as 10.8t.

That is, with the operation changeover switch 9 turned to the normally closed contact 9a side, the feedback resistor 21 is adjusted to m, and the pointer of the meter 22 is set to 1.
Just set it to the 0.8t scale.

At this stage of the calibration operation, the pointer of the meter 22 is set to 10.8 t.
Full scale (1
The measured value may be corrected so that the measured value becomes 0t scale).

In this case, the previously determined output voltage Ec of the correction value generation circuit 8
=1.016V is applied to the input resistor 20' via the operation changeover switch 9, so the variable resistor 21 is set so that the meter 22 is at full scale. At this point, no load is applied to the load converter, so
The output Eo of the bridge circuit 15 is 0. Therefore, the voltage applied to the input resistor 20 is also maintained at Ov. Here, if the gauge factor = 2.0 and the supply current I to the bridge circuit 15 = 2 mA, the gain G at this time is the following (11
) From the formula, Et=IV and find the gain G, G=
4 ・Et /K・I ・Ec =984.25...
(12) By setting the gain of the gain setting circuit 3 to G=984.25, it is possible to calibrate the load converter with the above rating at 2000 με.

Next, the operation selector switch 9 is turned to the MEAS side, that is, the normally closed contact 9b is closed, the voltage applied to the input resistor 20' is set to Ov, and the measurement operation is started. If an unknown load to be measured is applied to the load transducer (for convenience of explanation, this load is assumed to be 10 t), the rated strain of the load transducer is 1850 μE, so the bridge output terminal 17. The voltage EO between 17' and
10-11X2X10-3X508+4'=0.939
8 xlO-3V (13) Since the voltage follower 18 has a one-to-one ratio of input and output, substituting equations (12) and (13) into equation (8), Et = G-Eo = 984.25 xo, 9398
X10-3=0.925V...(14)
That is, since the full scale is V, the meter 22 is indicating 9.25t. Therefore, from formula (4), true value = (2000/1850)X9.25 t=1
0t...(15), and now the unknown load applied to the load converter is 10
t.

As mentioned above, according to this embodiment, the correction value generation circuit 8 is
Since it is composed of digit digital switches, it can be set to any nominal gauge resistance in 1Ω increments from at least 1 to 999Ω (of course, it may also be based on the actual measured resistance value of the strain gauge).
can be set, and therefore, the calibration value can be corrected for the gauge resistance in 1Ω increments from 1 to 999Ω, making it a strain measuring instrument that further expands the advantages of the constant current drive method, which is unaffected by the wire resistance r of the connecting cable. can be obtained.

In other words, in the case of the constant current drive method, if the calibration value can be corrected using the gauge resistance, it can only be used with strain gauges with one type of gauge resistance, and as mentioned above,
Even if correction could be made, conventionally it could only be corrected for two types of resistance, 120Ω and 350Ω. If we try to increase the number of gauge resistances that can be corrected using the conventional method, the number of parts will be enormous (even by simple calculation, we will need more than 999 fixed resistors and more than 999 contacts to switch them), and If the number of parts increases, the number of assembly man-hours increases, and the number of man-hours for adjustment, inspection, etc. becomes enormous, making it virtually impossible to manufacture. However, according to the above-mentioned embodiment, the number of parts is small and the number of man-hours for assembling increases, and the number of man-hours for adjustment and inspection becomes enormous. From 1 to 999Ω, that is, 99
Nine types of corrections are possible, making it possible to deal with practically any gauge resistance. As a result, it is possible to improve measurement accuracy and improve the operability of calibration and measurement while taking advantage of the advantages of the constant current drive method.

It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the spirit thereof.

For example, the calibration value generation circuit 6 can be provided on the output side of the correction value generation circuit 8, or if it is configured to be disconnected from the measurement system during measurement using a switch, the gain adjustment circuit 3
It is also possible to provide it on the output side.

Furthermore, the resistance value setting circuit 7 and the correction value generation circuit 8 are not limited to a three-digit configuration, but can also be configured with three or more digits or three digits or less, and are not limited to integers, but can also be configured to set decimal points. is also possible. In this case, for example, an 87
Settings such as ゜5Ω are possible, further improving practicality.

Furthermore, the display circuit 4 is not limited to the meter 22, and is not limited to analog display; a digital meter equipped with an A/D converter can also be used as the display circuit 4. Further, it is also possible to provide an external output terminal at the output of the gain setting circuit 3 and connect it to an analog recorder, such as a pen recorder, an electromagnetic oscilloscope, or the like.

Furthermore, in the calibration value generation circuit in the above embodiment,
Although it can only output calibration value voltages corresponding to several predetermined calibration values such as 50με, 100μf, 500μE, etc., it has the same configuration as the resistance value setting circuit 7 and correction value generation circuit 8, and has a 5-digit number of digits. Then, 1 με ~ 100
Calibration values in lμE can be generated over a range of 00μE. Therefore, in this case, calibration can be easily performed without performing proportional calculations such as equations (11) and (15).

Further, in the embodiment, the operation changeover switch 9 is provided between the output end of the correction value generation circuit 8 and the input resistor 20', but in FIG.
The output end of the voltage follower 18 is separated from the output end of the voltage follower 18, the common contact 9c is connected to one end of the input resistor 20, the normally open contact 9a is connected to the output end of the correction value generation circuit 8, and the voltage follower The normally closed contact 9b may be connected to the output end of the wire 18. With this configuration, not only can the input resistor 20' be eliminated, but also calibration can be performed regardless of whether or not a load (load, pressure, force, etc.) is applied to the conversion section during calibration. , -layer advantageous.

(e) Effects As detailed above, according to the present invention, with a simple configuration,
Regardless of the resistance value of the strain gauge assembled in the measurement bridge to which the constant current source is applied, it is possible to generate an accurate calibration value voltage that is corrected according to the resistance value, and it is extremely easy to operate. It is possible to provide a calibration device for a strain measuring instrument that is simple and can enjoy all the advantages of a constant current drive system.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a calibration device for a strain measuring instrument according to the present invention, FIG. 2 is a circuit diagram showing a specific circuit configuration of the same embodiment, and FIG. FIG. 4 is a circuit diagram showing the specific circuit configuration of the correction value generation circuit, which is the main part of the present invention, and FIG. 5 is a circuit diagram showing the principle circuit configuration of the constant current source used in the present invention. , is a block diagram of a conventional device. DESCRIPTION OF SYMBOLS 1... Conversion section, 2... Buffer amplifier circuit, 3... Gain setting circuit, 4... Display circuit, 5... Standard Voltage generation circuit, 6... Calibration value generation circuit, 7... Resistance value setting circuit, 8... Correction value generation circuit, 9... Operation selector switch , 10...Current detection circuit, 11...Comparison circuit, 12...Current control circuit, 13...Unregulated power supply, 14...・・Constant current source, 15・・Wheatstone bridge circuit, 18・
...Voltage follower, 19...Operation amplifier, 20.20'...Input resistance, 21...Variable resistor for gain setting, 22...・
...Meter, 23...Reference power supply, 24-29...Calibration value generation voltage dividing resistor, 30.
...Calibration value selection switch, 31...Resistance value control output signal, 35a to 35e, 36a to 36e, 3
7a~37e...Analog switch, 38a~
38e, 39a-39e, 40a-40e, 46a-4
6c...Input resistance, 41a to 41c, 42...
...Operation amplifier, 43a to 43c, 45...
・Feedback resistor, 52...3-digit digital switch.

Claims (1)

[Claims] (1) A strain measuring instrument that applies a constant current from a bridge power source to a measurement bridge consisting of a resistance bridge using a strain gauge, amplifies the output obtained from the measurement bridge, and obtains a measurement output, has a certain reference resistance value. A calibration value generation circuit that generates a calibration value voltage equal to a voltage corresponding to a predetermined amount of strain output from a measurement bridge composed of strain gauges, and a resistance value of the strain gauges constituting the measurement bridge serve as the above reference. A resistance value setting circuit that can numerically set the resistance value of the strain gauge when it differs from the resistance value and outputs a setting signal corresponding to the numerically set resistance value, and a resistance value setting circuit that outputs a setting signal corresponding to the numerically set resistance value; A calibration value voltage that is corrected by multiplying the calibration value voltage of the calibration value generation circuit by the ratio between the resistance value set by the setting signal of the resistance value setting circuit and the reference resistance value is obtained by inserting the circuit into the circuit. a correction value generation circuit that selectively receives the corrected calibration value voltage and the output of the measurement bridge, and adjusts the corrected calibration value voltage to a predetermined level by a gain set by an external operation. A calibration device for a strain measuring instrument, comprising: a gain setting circuit that receives the output of the measurement bridge and outputs a measurement output that is correlated with the corrected calibration value voltage.