JPH0810121B2 - Calibration device for strain measuring instrument - Google Patents

Description

Description: (a) Technical Field The present invention relates to a calibration device for a strain measuring instrument, and more specifically, a constant current is applied from a bridge power source to a measurement bridge formed of a resistance bridge using a strain gauge to perform the measurement. The present invention relates to a calibration device in a strain measuring instrument that amplifies an output obtained from a bridge to obtain 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 an input side in order to convert a strain amount into an electric amount. Fifth
As shown in the figure, when the bridge power supply 62 for applying the voltage E is connected to the input terminals 61 and 61 'of the Wheatstone bridge 60 in which the input resistance and the output resistance are both Rg,
Bridge output voltage Eo between output terminals 63 and 63 'and input terminal 61,
The relationship between the bridge input voltage Ei between 61 'will be described. still,
64, 64 'are bridge power supply 62 to bridge input terminals 61, 61'
Is the line resistance of the connecting cable up to and r is its resistance value.

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

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

Ei = {Rg / (Rg + 2r)} · E (1) Therefore, when the connecting cable is long, the line resistance r increases and the difference occurs. If the remote sensing method is used to remove this difference, a separate wiring for remote sensing is required, and the distance from the bridge power source 62 to the bridge input terminals 61, 61 'is long (may reach 1000 m). In this case, the wiring for remote sensing is not only uneconomical, but also the workability of installation and wiring is reduced.

On the other hand, in the case of the constant current drive system, the bridge input voltage
Ei has the relationship of equation (2).

Ei = I · Rg (2) In this case, since the power supply current I is constant, the influence of the line resistance r is eliminated. However, as can be seen from the equation (2), when the bridge resistance Rg changes, that is, when the strain gauge having a different resistance (nominal gauge resistance) is replaced in the actual measurement, the input voltage Ei changes. Generally, when the bridge circuit shown in FIG. 5 is composed of strain gauges, the expression (3) is established.

Eo = K · ε · Ei / 4 (3) However, in the above formula (3), K is the gauge factor and ε is the strain. Therefore, the measured bridge output voltage
Since Eo should originally be a function of only strain ε, there is a disadvantage that the bridge input voltage Ei is added as a variable, so that accurate measurement cannot be performed or only one type of strain gauge strain gauge can be used. Therefore, a calibration value corrected by a plurality of gauge resistances, for example, a calibration value 2000με, 1000με, 500με, etc., which are corrected to fit the Wheatstone bridge composed of strain gauges having nominal gauge resistances of 120Ω and 350Ω, respectively. A calibration device for providing a value generation circuit 65, appropriately selecting a calibration value generated by the selection switch 66 according to the nominal gauge resistance of the strain gauge used, and turning on the calibration operation switch 67 and injecting it into the gain adjustment circuit 68 is already available. It is considered. That is, in this calibration device, the calibration value generation circuit
The calibration value voltage from 65 is injected into the gain adjustment circuit 68, and the gain of the amplifier 68b is adjusted by the variable resistor 68a that can be operated externally, and the pointer of the meter (indicator) 69 is set to the full scale position or a predetermined scale line. The reference position (reference value) can be set together. In the calibration device of FIG. 5 configured in this way, for example, a load transducer in which a Wheatstone bridge 60 is assembled by a strain gauge having a gauge resistance of 120Ω, and a rated capacity of 1850 με
A case of calibrating a load converter that generates a strain of (με: 10 ^-6 strain) will be described.

First, of the calibration values that can be generated by the calibration value generation circuit 65, a value that is closest to the strain amount 1850 με, for example 2000 με, is selected (the selection mechanism is not shown). Then, from the calibration value generation circuit 65, the 2000
A calibration value voltage (generally 1 με = 1 μv) corresponding to με is output and injected into the gain adjustment circuit 68. Since the calibration value 2000 με output from the calibration value generation circuit 65 and the rated strain 1850 με of the load converter are different, 2000 με
The load corresponding to ε is calculated by the following equation (4).

(2000/1850) × 10≈10.8 (t) (4) This 2000με calibration value output (voltage or waveform) is 10.8
Calibrate the measured output as t. That is, variable resistor 6
Adjust 8a and adjust the pointer of meter 69 to the 10.8t scale. Next, when the calibration operation switch 67 is turned off and the load to be measured is applied to the load converter, the soft bridge output voltage Eo is input to the gain adjustment circuit 68 via the buffer amplifier 70 and the meter is read. Displayed on 69.

However, the above calibration device can correct the calibration value only for the nominal gauge resistance of 120Ω and 350Ω. The above is one of the commonly used gauge resistors.
In addition to 120Ω and 350Ω, there are 500Ω, 1000Ω, etc. In addition, there are many cases in which a plurality of converters (bridge circuit 60) are connected in parallel, and considering the gauge resistance combined in this way, Gauge resistances will exist innumerably, and it is practically impossible to generate calibration values for such various kinds of gauge resistances.

On the other hand, it is ideal that a calibration value that can be calibrated as a strain measuring instrument can be set continuously, but in reality, there is no fractional value, for example, a calibration value with a limited multiple relationship, such as 2000 μ.
The configuration is such that ε, 1000 με, 500 με, 100 με, 50 με, etc. are generated in stages. Therefore, even if the nominal gauge resistance is limited to four types of 120Ω, 350Ω, 500Ω, and 1000Ω, and the calibration value is limited to five types of 2000με to 50με, each of the above calibration values for each nominal gauge resistance There are 4 × 5 = 20 kinds of combinations to correct (including overlapping combinations). Furthermore, if an attempt is made to make a configuration that can be corrected by the above-described synthesized nominal gauge resistance, the number of parts will increase to an unrealistic number and become bulky, making it almost impractical.

(C) Purpose The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a simple circuit configuration, even if the gauge resistance of a strain gauge incorporated in a measurement bridge has any value. An object of the present invention is to provide a calibration device for a strain setting device that can always generate an accurate calibration value voltage, is extremely easy to operate, and can fully enjoy the advantages of the constant current drive system.

(D) Configuration In order to achieve the above-mentioned object, the present invention applies a constant current from a bridge power supply to a measurement bridge composed of a resistance bridge using a strain gauge and amplifies an output obtained from the measurement bridge to obtain a measurement output. In the strain measuring device, a calibration value generating circuit that generates a calibration value voltage equal to a voltage corresponding to a predetermined strain amount output from a measurement bridge composed of a strain gauge having a certain reference resistance value,
When the resistance value of the strain gauge that constitutes the measurement bridge is different from the reference resistance value, the resistance value of the strain gauge can be numerically set, and the resistance value that outputs a setting signal corresponding to the numerically set resistance value. The calibration value is generated by inserting a circuit between the setting circuit and the input side or the output side of the calibration value generating circuit, and calculating the ratio between the resistance value set by the setting signal of the resistance setting circuit and the reference resistance value. A correction value generating circuit for multiplying the calibration value voltage of the circuit to generate a corrected calibration value voltage, and the corrected calibration value voltage selectively receiving the corrected calibration value voltage and the output of the measurement bridge. Is adjusted to a predetermined level by the gain set by an external operation and is output, and the output of the measurement bridge is received and the measurement output related to the corrected calibration value voltage is output. Is constructed by having a gain setting circuit for outputting.

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

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a calibration device in a strain measuring instrument according to the present invention.
The drawing is a circuit diagram showing a circuit configuration of the embodiment.

In FIG. 1, reference numeral 1 denotes a Wheatstone bridge circuit configured to include a strain gauge on at least one side, that is, a measurement bridge and conversion of a load converter, a pressure converter, a displacement converter or the like for converting a physical quantity into an electric quantity. Is a department
Reference numeral 2 is a buffer amplifier circuit having an amplification degree of “1” by a voltage follower or the like which receives the electric quantity from the conversion unit 1. Reference numeral 3 denotes a gain setting circuit that receives the output of the buffer amplifier circuit 2 and that is a variable gain amplifier whose gain can be externally set by a conversion resistor or the like, and 4 is a display circuit such as a meter that analog-displays the output of the gain setting circuit 3. is there. Reference numeral 5 is a reference voltage generating circuit that holds a constant voltage, and 6 is a calibration value generating circuit that divides the output voltage of the reference voltage generating circuit to generate a predetermined calibration value. Reference numeral 7 is a resistance value setting circuit configured by using three digits (three) of digital switches each having a 4-bit BCD output, and 8 is a resistance value setting circuit 7 for the output voltage of the calibration value generating circuit 6. It is a correction value generation circuit for generating a corrected calibration value voltage by multiplying the calibration value voltage by a ratio (coefficient) of a resistance value set in step 1 to a reference resistance value described later. Reference numeral 9 is 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, the calibration operation is performed when the normally open contact 9a is closed (when it is tilted to the side displayed with the CAL character), and when the normally closed contact 9b is closed (displayed with the MEAS character). (When it is pushed down to the side), the measurement operation is performed. On the other hand, 10 is a current detection circuit for detecting the supply current for driving the Wheatstone bridge circuit of the conversion unit 1, and 11 compares the output of the current detection circuit 10 with the output of the reference voltage generation circuit 5. Reference numeral 12 is a comparison circuit that outputs a control signal, 12 is a current control circuit that keeps the drive current supplied to the conversion unit 1 constant based on the control signal from this comparison circuit, and 13 is the control of this current control circuit 12. It is an unstabilized power source that receives A constant current source 14 is composed of the reference voltage generation circuit 5, the current detection circuit 10, the comparison circuit 11, the current control circuit 12 and the unstabilized power supply 13.
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, 15 includes a strain gauge having 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 having Rg with substantially the same resistance value for both input resistance and output resistance. The bridge input terminals 16 and 16 'are connected to a constant current source 14 as a bridge power source, and 17 and 17' are bridge output terminals. The bridge input terminal 16-
The voltage between 16 'is referred to as a bridge input voltage and is referred to as Ei, and the voltage between the bridge output terminals 17-17' is referred to as a bridge output voltage and is referred to as Eo. Reference numeral 18 is a voltage follower having an input impedance sufficiently larger than the bridge output resistance Rg so as not to give a disturbance to the bridge circuit 15, and outputs 1 μV for 1 με strain of the strain gauge, and a bridge is provided at its input end. Output terminals 17 and 17 'are connected to each other.

Reference numeral 19 is an operational amplifier whose non-inverting input terminal is grounded. 20, 20 'are input resistors having the same resistance value Ri, one end is commonly connected 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. Reference numeral 21 is a feedback resistor composed of a variable resistor, which is connected between the inverting input terminal and the output terminal of the operational amplifier 19. The input resistances 20 and 20 ', the feedback resistance 21 and the operational amplifier 19 constitute an inverting addition amplifier, and this circuit portion will be referred to as a gain setting circuit 3 hereinafter. 22 is a meter as the display unit 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 the gain setting circuit 3 is 1V, full scale is instructed. On the other hand, reference numeral 23 is a reference power source as the reference voltage generating circuit 5, the negative end of which is grounded and its output voltage is represented by Es. 24 to 29 are voltage dividing resistors for generating the calibration value,
Each resistance value is represented by r ₁ to r ₆ . 30 is a calibration value selection switch composed of a rotary switch that can be operated externally, and 30a to 30e are 2000 με contacts, 1000 με contacts,
There are 500 με contact, 100 με contact and 50 με contact, 30
f is a common contact. One end of the voltage dividing resistor 24 is connected to the positive terminal of the reference voltage 23, and the other end is connected in series to the voltage dividing resistor 25.
Grounded through ~ 29. Also, 2000με contact 30a
Is connected to the connection point of voltage dividing resistors 24 and 25, and so on.
00με contacts 30b to 50με contacts 30e are
And 26, voltage dividing resistors 26 and 27, voltage dividing resistors 27 and 28, voltage dividing resistor 28 and
Connected to 29 connection points. The circuit portion (the portion surrounded by the broken line in the figure) including the voltage dividing resistors 24 to 29 and the calibration value selection switch 30 constitutes the calibration value generating circuit 6. Also, when the output voltage of each of the 2000 με to 50 με contacts is expressed as V _{1 to} V ₅ , the resistance value r _{1 of the} voltage dividing resistors 24 to 29 is
The relationship with r ₆ is configured as in the following equation (5).

_{"V 1 = {(r 2 +} r 3 + r 4 + r 5 + r 6) / r 0} · Es = 2000μV V 2 = {(r 3 + r 4 + r 5 + r 6) / r 0} · Es = 1000μV V 3 = {(R ₄ + r ₅ + r ₆ ) / r ₀ } ・ Es = 500 μV V ₄ = {(r ₅ + r ₆ ) / r ₀ } ・ Es = 100 μV V ₅ = (r ₆ / r ₀ ) ・ Es = 50 μV ” (5) However, r ₀ = r ₁ + r ₂ + r ₃ + r ₄ + r ₅ + r ₆ The common contact 30f is connected to the input end of the correction value generating circuit 8, and the output end of this correction value generating circuit 8 is It is connected to the normally open contact (CAL side contact) of the operation changeover switch 9. 31
Numerals 33 are resistance value control output signals as setting signals each consisting of 4 bits of each digit of the resistance value setting circuit 7, 31 is a least significant digit, and 33 is a most significant digit resistance value control output signal.

FIG. 3 is a circuit diagram showing a concrete embodiment of the correction value generating 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 generating circuit 6. 35a ~ 35e, 36a ~ 36e
And 37a to 37e are analog switches, I is an input terminal, O 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 O are connected, and the analog switch is opened at L level. 38a-38e, 39a-39e and 40a
Input resistances 38a, 38b, 38c, and 38d are 8Ω, 4Ω, 2Ω, and 40e, respectively.
1Ω, and these resistance values are input resistance 39a ~ 39d, 40a ~
The same is true for 40d. The resistance values of the input resistors 38e, 39e, 40e are 800Ω, 80Ω, 8Ω, respectively. 41a to 41c and 42 are operational amplifiers, respectively, whose non-inverting input terminals are grounded to form an inverting amplifier. Reference numerals 43a to 43c are feedback resistors connected between the inverting input terminal and the output terminal of the operational amplifiers 41a to 41c, respectively, and the respective resistance values are 800Ω and 80
Ω, 8Ω. The input resistors 38a to 38e are commonly connected at one end to the inverting input end of the operational amplifier 41a, and the other ends are connected to the output terminals O of the analog switches 35a to 35e, respectively. Then, the input terminals I of the analog switches 35a to 35e, 36a to 36e and 37a to 37e.
Are commonly connected to the calibration value input terminal 34. In addition, analog switches 36a to 36e and
Input terminals 39a to 39e are connected to the output terminals O of 37a to 37e, respectively.
And 40a to 40e have one ends connected in series and the other ends connected in common and connected to the inverting input terminals of the operational amplifiers 41b and 41c, respectively. Reference numeral 45 is a feedback resistor having a resistance value R connected between the inverting input terminal and the output terminal of the operational amplifier 42, 46a to 46c are input resistors having a resistance value R, and one ends thereof are output terminals of the operational amplifiers 41a to 41c, respectively. , And the other end is commonly connected to the inverting input end of the operational amplifier 42. Reference numeral 47 is an output terminal of the correction value generating circuit 8 and is connected to the normally open contact (CAL side contact) 9a of the operation changeover switch 9. The output end of the operational amplifier 42 is the correction value generating circuit 8 described above.
Connected to the output terminal 47 of.

On the other hand, 48a to 48c are negative logic inputs having four input terminals.
AND gate, each output terminal is analog switch 3
It is connected to the control input terminals C of 5e, 36e and 37e. Four
9a to 49d, 50a to 50d and 51a to 51d are 4-bit BCD signals, and analog switches 35a to 35d and 36a, respectively.
.About.36d and 37a.about.37d are connected to the control input terminals C in a one-to-one manner and are also connected in a one-to-one manner with the respective input terminals of the negative logic input AND gates 48a to 48c. Note that 49a, 50a, 51a are the least significant bits (LSB), and 49d, 50d, 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 are resistance value control output signals 31 to, respectively.
Corresponding to 33, B1 is the first 4-bit BCD output terminal, B2 and B3 are the tenth and 100th 4-bit BCD output terminals, respectively, and I is the power input terminal for generating a signal, + 5V is supplied, and G Is a common contact terminal and is grounded. Also, 53a to 53c are knobs for numerically setting the 1st, 10th, and 100th resistance values, respectively, and can be set from 0 to 9; 54a to 54c are the numerical values set by the setting knobs of the above digits 0 to 0. It is each display window which displays 9.

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

In the figure, 55 is a current detection resistor as the current detection circuit 10 in FIG. 1, 56 is an error amplifier as the comparison circuit 11, 57 is a control transistor as the current control circuit 12, 5
Reference numerals 8 and 58 'denote constant current output terminals as a bridge power source, which are respectively connected to the bridge input terminals 16 and 16' of FIG. One end of the current detection resistor 55 is connected to the output terminal 58 and the inverting input end of the error amplifier 56, and the other end is grounded and connected to the negative side of the unstabilized power supply 13. The positive terminal of the reference power source 23 as the reference voltage generating circuit 5 is connected to the non-inverting input terminal of the error amplifier 56,
The base of the control transistor 57 is connected to the output terminal of the error amplifier 56, the collector of the control transistor 57 is connected to the positive side of the unstabilized power supply 13, and the emitter is connected to the output terminal 58 '.

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

When the voltage generated by the current supplied from the unregulated power supply 13 flowing in 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,
When Er is small, the base potential of the control transistor 57 is increased to increase the supply current. Conversely, when Er is larger than Es, the base potential of the control transistor 57 is decreased to decrease the supply current. As a constant current.

Now, the operation of the entire embodiment except for the constant current source 14 will be described.

Now, when the sensor connected as the input of the strain measuring instrument is a load transducer with a rated capacity of 10t and a rated strain of 1850με, and the strain gauge that constitutes the bridge circuit 15 has a nominal gauge resistance of 508Ω Will be described as an example. First, as the operation for calibration, the calibration value closest to the above rated strain of 1850 με is selected as the calibration value selection switch.
Select by 30 (Fig. 2). That is, in this case, the selection switch 30 is turned to connect the common contact 30f to the 2000 με contact 30a. 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 setting knobs 53b and 53c are turned so that the display in the tenth place display window 54b is "0" and the display in the 100th place display window 54c is "5". Further, the operation selector switch 9 is tilted to the CAL side. In the case of this example, the voltage input to the calibration value input terminal 34 (FIG. 3) is based on the assumption that the resistance value of the strain resistance (reference resistance) of the strain gauge constituting the measurement bridge is 1Ω. A voltage of 2000 μV corresponding to 2000 με is applied. The BCD corresponding to the decimal number "8" is output from the 1st digit BCD output terminal B1 of the digital switch 52, and the BCD corresponding to the decimal number "0" is output from the 10th digit BCD output terminal B2. 1 from BCD output terminal B3
The BCD corresponding to the decimal number "5" is output. That is, the BCD output signals 51a to 51c in the first digit are at the L level and the BCD output signal 51d is at the H level, and the BCD output signals in the tenth digit BCD output signals 50a to 50d.
Are all L level, and 49 of 100 digit BCD output signals
a is H level, 49b is L level, 49c is H level, 49d is L level
Level. Therefore, in the circuit of the 100th digit, the analog switches 35a and 35c are turned on and the input resistors 38a and 38c are effective as the input resistors of the operational amplifier 41a. The combined input resistance is 16 / 10Ω, and the feedback resistance 43a is 800Ω.
Therefore, the operational amplifier 41a operates as an inverting amplifier having an amplification factor of 500 times. Further, in the circuit of the tenth digit, the analog switches 36a to 36d are in the non-operating state, the output of the negative logic input AND gate 48b becomes the H level, only the analog switch 36e is turned on, and the inverting input terminal of the operational amplifier 41b is input. It is installed through resistor 39e and its output is kept at 0V. Next, in the first digit circuit, analog switch 37
Only d is turned on, and only the input resistance 40d becomes effective as the input resistance of the operational amplifier 40c. Therefore, the operational amplifier 41c operates as an inverting amplifier having an amplification factor of 8 times. When these results are shown by numerical values, the output voltage of the operational amplifier 41 is
2000 (μV) × 500 = 1 (V), the output voltage of the operational amplifier 41c is 2000 (μV) × 8 = 0.016 (V),
It is added by the addition amplifier consisting of operational amplifier 42 and is 1 + 0.01.
6 = 1.016V, calibration value 2000με is nominal gauge resistance 503
Output voltage 1.016V corrected by Ω is output from the output terminal 47.

Now, if the nominal gauge resistance and the bridge resistance are equal Rg (generally configuring the bridge as such),
Since the bridge input voltage Ei is a constant current drive system, when a constant supply current is I, the formula (6) is obtained.

Ei = IRg (6) Eo = KεIRg / 4 (7) Also, substituting the above equation (6) into the equation (3) shown in the prior art section, (7) The formula is obtained.

Therefore, assuming an arbitrary amplification system with a gain of G and an output of Et, and when Eo shown in the above equation (7) is input to this amplification system, the input / output relations are equations (8) and (8). ′ Becomes the formula.

Et = G · Eo (8) Et = G · K · ε · I · Rg / 4 (8) ′ The output Ec of the correction value generation circuit is the distortion of the bridge circuit 15 that receives the constant current I. Resistance value Rs that is the gauge reference
Assuming 1Ω, Ec = ε · Rg / Rs = ε · Rg (9) From equation (8) ', the following equation (10) is obtained.

Et = G · K · I · Ec (10) Therefore, if the output of the gain setting circuit 3 is Et, the gain setting circuit 3 is realized as an amplifier having the gain G in the equation (10). .

By the way, since the corrected correction value 2000 με output from the correction value generation circuit 8 is deviated from the rated strain 1850 με of the load converter, the load corresponding to 2000 με generated in the load converter is calculated by the following formula (11). calculate.

(2000/1850) × 10 = 10.8 (t) (11) Calibrate the measured output with this 2000 με calibration value output set to 10.8 t.

That is, the feedback resistance 21 is adjusted with the operation changeover switch 9 tilted to the normally open contact 9a side, and the pointer of the meter 22 is adjusted to 10.8t.
It should be adjusted according to the scale.

At the stage of this calibration operation, the measured value may be corrected by not adjusting to the pointer 10.8t of the meter 22 but adjusting to a full scale (scale of 10t) as described below. In this case, since the output voltage Ec = 1.016V of the correction value generating circuit 8 obtained above is applied to the input resistance 20 'through the operation changeover switch 9, the variable resistor 21 is set so that the meter 22 becomes full scale. Set. At this point in time, since no load is applied to the load converter, the output Eo of the bridge circuit 15 is 0V, so the voltage applied to the input resistor 20 is also 0V. Here, if the gauge factor K = 2.0 and the supply current I to the bridge circuit 15 is 2 mA, the gain G at this time is 1V when the full scale of the meter 22 is 1V.
Therefore, from the following equation (11), set Et = 1V and gain G
Then, G = 4 · Et / K · I · Ec = 984.25 (12), and by setting the gain of the gain setting circuit 3 to G = 984.25, the load transducer with the above rating can be calibrated at 2000 με. It will be.

Next, the operation changeover switch 9 is tilted to the MEAS side, that is, the normally closed contact 9b is closed, the applied voltage to the input resistor 20 'is set to 0V, and the measurement operation is started. And an unknown load to be measured by the above load converter (However, for convenience of explanation, this load is 10t
Is applied), the above load transformer /
Since the rated strain of is 1850 με, the bridge output terminal 1
The voltage Eo between 7,17 'is Eo = K ・ ε ・ I ・ Rg / 4 = 2.0 × 1850 × 10 ^-6 × 2 × 10 ^-3 × 508 ÷ 4≈0.9398 × 10 ^-3 from the equation (7). V ... (13) And the voltage follower 18 has 1: 1 input and output
Therefore, by substituting the equations (12) and (13) into the equation (8), Et = G · Eo = 984.25 × 0.9398 × 10 ⁻³ = 0.925V …… (14) That is, the full scale (10t Since the scale) is 1V, the meter 22 indicates 9.25t. Therefore, (4)
From the formula, the true value = (2000/1850) × 9.25t = 10t (15), and now the unknown load applied to the load converter is
Measured as if it was 10t.

As described above, according to the present embodiment, since the correction value generating circuit 8 is composed of a 3-digit digital switch, any nominal gauge resistance (of course, the strain gauge's peculiar to the strain gauge is required) in increments of at least 1 to 999 Ω in increments of 1 Ω. It may be measured resistance value)
Since the calibration value can be corrected for the gauge resistance in 1Ω increments from 1 to 999Ω, strain measurement that further expands the advantages of the constant current drive method that is not affected by the line resistance r of the connecting cable You can get a vessel.
That is, in the case of the constant current drive system, if the calibration value can be corrected by the gauge resistance, it is possible to deal with only one type of gauge resistance strain gauge, and as described above,
Even if the correction could be made, in the past, at most 120Ω and 350
It could only be corrected with two types of Ω. And if you try to increase the number of gauge resistances that can be corrected by the conventional method, the number of parts will be huge (even with simple calculation, the fixed resistor has 999
More than 999 contacts are required to switch between them, and if the number of parts increases, the assembly man-hours also increase, and the man-hours for adjustments and inspections also increase, making it virtually impossible to manufacture. According to the embodiment, it is possible to correct 1 to 999Ω, that is, 999 kinds of corrections as described above with a small number of parts, and practically any gauge resistance can be supported. As a result, while taking advantage of the constant current drive method, it is possible to improve the measurement accuracy and the calibration / measurement operator.

It should be noted that the present invention is not limited to the above-described embodiments, but can be carried out by being variously modified without departing from the scope of the invention.

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

In addition, the resistance value setting circuit 7 and the correction value generating circuit 8 are 3
The configuration is not limited to the digit configuration, and the configuration having three digits or more or the three digits or less is possible. Further, the configuration is not limited to the integer, and the configuration can be set to the decimal point. In this case, for example, 87.5 in which four bridge circuits with a bridge resistance of 350Ω are connected in parallel.
It is possible to set Ω etc., and the practicality is further improved.

Further, the display circuit 4 is not limited to the meter 22, and further, not limited to analog display, it is possible to use a digital meter provided with an A / D converter as the display circuit 4.
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 or an electromagnetic oscillograph.

Further, in the calibration value generation circuit in the above embodiment, only the calibration value voltage corresponding to several predetermined calibration values such as 50 με, 100 με and 500 με can be output, but the resistance value setting circuit 7 and the correction value generation circuit If the circuit 8 has the same configuration as that of the circuit 8 and the number of digits is five, it is possible to generate a calibration value in units of 1 με over a range of 1 με to 10000 με. Therefore, in this case, the calibration can be easily performed without performing the proportional calculation and the like like the equations (11) and (15).

Further, in the embodiment, the operation changeover switch 9 is provided between the output end of the correction value generating circuit 8 and the input resistor 20 ', but in FIG. 2, one end of the input resistor 20 (the output end side of the voltage follower 18 is provided. ) And the output end of the voltage follower 18 are separated from each other, the common contact 9c is connected to one end of the input resistor 20, and the normally open contact 9a is connected to the output end of the correction value generating circuit 8.
The normally-closed contact 9b may be connected to the output end of 18. With this configuration, not only the input resistance 20 'can be eliminated, but also the load (load, pressure,
It is more convenient because the calibration can be performed regardless of whether or not a force is applied.

(E) Effects As described in detail above, according to the present invention, the resistance value of the strain gauge incorporated in the measurement bridge to which the constant current source is applied is simple, regardless of the resistance value. It is possible to provide a calibration device in a strain measuring instrument that can generate an accurate calibration value voltage corrected according to the above, and is extremely easy to operate and can fully enjoy the advantages of the constant current drive system.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a calibration device in a strain measuring instrument according to the present invention, FIG. 2 is a circuit diagram showing a concrete circuit configuration of the embodiment, and FIG. FIG. 4 is a circuit diagram showing a concrete circuit configuration of a correction value generating circuit which is an essential part of the present invention, FIG. 4 is a circuit diagram showing a principle circuit configuration of a constant current source used in the present invention, and FIG. FIG. 7 is a block diagram of a conventional device. 1 ... conversion part, 2 ... buffer amplification circuit, 3 ... gain setting circuit, 4 ... display circuit, 5 ... reference voltage generation circuit, 6 ... calibration value generation circuit, 7 ... resistance value setting circuit, 8 ... Correction value generation circuit, 9 ... Operation changeover switch, 10 ... Current detection circuit, 11 ... Comparison circuit, 12 ... Current control circuit, 13 ... Unstabilized power supply, 14 ... Constant current source, 15 …… Wheatstone bridge circuit, 18 …… Voltage follower, 19 …… Operational amplifier, 20,20 ′ …… Input resistance, 21 …… Gain setting variable resistor, 22 …… Meter, 23 …… Reference power supply, 24 to 29 …… Division resistance for generating calibration value, 30 …… Calibration value selection switch, 31 …… Resistance control output signal, 35a to 35e, 36a to 36e, 37a to 37e …… Analog switch, 38a to 38e, 39a to 39e, 40a to 40e, 46a to 46c …… Input resistance, 41a to 41c, 42 …… Operational amplifier, 43a to 43c, 45 …… Feedback resistance, 52 …… 3 digit digital switch.

Claims (1)

[Claims] 1. A strain measuring instrument for obtaining a measured output by applying a constant current from a bridge power source to a measuring bridge consisting of a resistance bridge using a strain gauge to obtain a measured output. A calibration value generation circuit that generates a calibration value voltage equal to the voltage corresponding to a predetermined strain amount output from the measurement bridge configured by the strain gauge, and the resistance value of the strain gauge that constitutes the measurement bridge is the reference The resistance value of the strain gauge can be measured and set when it is different from the resistance value, and the resistance value setting circuit that outputs the setting signal corresponding to the numerically set resistance value and the input side or output of the calibration value generation circuit Circuit, and the ratio of the resistance value set by the setting signal of the resistance setting circuit to the reference resistance value is used to calculate the calibration value. A correction value generating circuit for multiplying the calibration value voltage of the circuit to generate a corrected calibration value voltage, and the corrected calibration value voltage selectively receiving the corrected calibration value voltage and the output of the measurement bridge. Is adjusted to a predetermined level by a gain set by an external operation and is output, and a gain setting circuit that receives the output of the measurement bridge and outputs a measurement output related to the corrected calibration value voltage is provided. A calibration device for a strain measuring instrument characterized by the following.