SU1569742A1 - Transducer of signals of strain-gauge signals - Google Patents

Abstract

The invention relates to instrumentation technology and can be used in strain gauges for measuring force, pressure, acceleration. The aim of the invention is to improve the accuracy of conversion by increasing the steepness and stability of the conversion characteristic in a wide range of temperatures - achieved by introducing a thermal-dependent resistive voltage divider 6, comparator 7, low-pass filter 4 and logic elements. The force effect on the strain gauge bridges 1 and 2 leads to a differential change in their transfer coefficients. This causes a change in the phase shift of the oscillations at the output of the adder 5. When the strain gauge bridges 1 and 2 are of the same type, and the resistive divider 6 is temperature-dependent, the temperature coefficients of the resistors forming the divider are equal in absolute value but opposite in sign (moreover, if the absolute values of the temperature coefficients are equal) divider resistors and temperature coefficients of sensitivity of the strain gauge bridges), the phase shift at the output of the adder 5 weakly depends on the change in the ambient temperature, strain gauges. 1 il.

Description

1

The invention relates to control and measuring equipment and can be used in strain gauges for measuring force, pressure, acceleration.

The aim of the invention is to improve the conversion accuracy by increasing the steepness and stability of the conversion characteristic over a wide range of temperatures.

FIG. 1 shows a functional diagram of a strain gauge signal converter; in fig. 2 is a vector diagram of the process of summing the oscillations in the adder.

The converter contains two resistive bridges 1 and 2, the inputs of which are connected, a reference generator 3 connected by an output to the inputs of the resistance-measuring bridges I and 2, a low-pass filter 4, the input of which is connected to the output of the resistive bridge 1, an adder 5, a thermal-dependent resistive the voltage divider 6 connected by the input to the output of the reference generator 3, and the output to the second input of the adder 5, the third input of which is connected to the output of the low-pass filter 4, a voltage comparator 7 whose inputs are connected to the outputs of the resistor bridges 1 and 2, D-flip-flop 8, the enable input of which is connected to the output of the voltage comparator 7, and the control input with its inverse output, the HE 9G logic element, electronic switches 10-13, and the HE 14 gate connected the input to the inverted output of the D-trigger 8 and the control input of the electronic switch 11, and the output to the control input of the electronic switch 13, the input of which is connected to the input of the electronic switch 11 and connected to the output of the strain-resistant bridge 2, while the output of the resistance-measuring bridge 1 soy Inen with the inputs of the electronic switch 10 and the electronic switch 12, the control input of which is connected to the non-inverse output of the D-flip-flop 8 and connected to the input of the HE 9 logic element connected by the output to the control input of the electronic switch 10, the output of which is connected to the output of the electronic switch 13 and is connected to the fourth (non-inverting) input of adder 5, the fifth input of which is connected to the outputs of electronic switches 11

and 12, a high-pass filter 15, a phase meter 16 connected by one input to the output of the reference generator 3, and the other to the output of the adder 5, the first input of which is connected to the output of the high-pass filter 15, the input connected to the output of the strain-resistant bridge 2, in addition An RC circuit is connected to the setup R-input of the D-flip-flop 8, which ensures that the flip-flop is set to the initial zero state.

The strain gauge bridges consist of resistors connected according to a bridge circuit (the so-called quadripoles -crossed connections) are tension-bridges in such a way that the force applied to them leads to equal in magnitude, but opposite in sign, changes transmission ratios. Moreover, in the initial state, one of the strain gauge bridges is balanced, and the second is unbalanced. The voltage comparator 7 is a specialized differential amplifier with a single digital output. The principle of the voltage comparator 7 is such that when the difference in input signals is less than some known trigger voltage level U ag, a potential corresponding to a logical unit is established at the output, and if the difference between the input signals is greater than this level, Ucpaj, then the potential corresponding to logical zero.

The electronic switches 10-13 are used to switch analog signals. If the switch is in the On state, its output voltage must be exactly equal to the input voltage; if the switch is in the Off state, it should become zero.

RC circuit, one poles of resistor 17 (R) and capacitor 18 (C) of which are connected and connected to the installation R-input of D-flip-flop 8, the second pole of resistor 17 is connected to the positive pole of the power source, and the second pole of capacitor 18 is connected to common bus, provides the initial setting of the trigger 8 to the zero state. The time constant of the DRC chain (R C) is chosen such that

that when the supply voltage is applied to one pole of the resistor 17, the capacitor 18 cannot be charged instantaneously and at the first moment of time a low level potential is applied to the installation R-input of the trigger, due to which the D-trigger is set to the zero state. After a time, the capacitor 18 is fully charged, and a high potential is applied to the R input of the trigger and the trigger retains the previously set (zero) state.

The Converter operates as follows.

In stationary mode, when there is no power effect, when, for example, the first strain gauge bridge 1 is most unbalanced and the second bridge 2 is balanced, the output oscillation U0 of the reference generator 3 with a frequency through the first strain gauge bridge 1 (U ,.) and filter 4

four

low frequency (U), where it acquires a phase shift equal to (provided that the low frequency Butter second order is used)

V,

 arctg 1 dg

the output of which the potential of a single level entering the control input of the first electronic switch 10 connects the output of the first strain gauge bridge 1 to the fourth (inverting) input of the adder 5, and the unit potential of the inverse output of the second D trigger 8 goes to the control input of the second

electronic switch 11, connects the output of the second strain gauge bridge 2 to the fifth input of the adder 5. In this case, the keys of the third electronic

5 of the switch 12, to the input of which a zero potential is supplied from the non-inverse output of the D-flip-flop 8, and the fourth electronic switch 13, to the control input of which is supplied the zero potential c. the output of the second logic element HE 14 is in the open state.

The process of summing the oscillations in the adder 5 for this case is shown in the vector diagram (Fig. 2a). The total phase shift at the output of the adder is

I / arctg

KiHilKJ cc2§l woofer (l4 4h90) .K,

(one)

where Sl, w0 / cJ () H4;

u

Fnch

- cut-off frequency of the low-pass filter 4,

comes to the third input of the adder 5, at the first input of which the voltage level is zero (since the second strain gauge bridge 2 is balanced and its transmission coefficient is zero), and the second input receives the oscillation C, with frequency u) 0 through a thermal-dependent resistive divider 6 voltages

Since in this mode of operation UU, a potential corresponding to a logical zero is set at the output of the comparator 7. In this case, a potential corresponding to a logical zero is supplied to the enable input of D-flip-flop 8, the inverse output of which is connected to its control input, and the non-inverse output of the D-flip-flop 8 is set to zero potential, and on the inverse - the potential corresponding to the logical unit. The zero potential from the non-inverse output, the stroke of the trigger 8 is fed to the input of the first logical element HE 9, with

where K „is the transmission coefficient of the first M1

the resistance strain gauge 1;

Kfnch modulus filter coefficient 4 low pass; Kn is the transfer coefficient of the thermodependent resistive voltage divider 6.

In dynamic mode if available

small force (Ј

e

“T-), where Ј is relative deformation., Sensitive deformation of the sensitive element; Јt is the maximum value of the relative deformation) the first strain gauge bridge 1 is unbalanced and the value

Its transmission coefficient is slightly less than the maximum, the second strain gauge bridge 2 is also unbalanced, and its transmission coefficient is different from zero. At the same time

U0 with frequency UJ0 through the second strain gauge bridge 2 (UM) and high-pass filter 15 (IL), where it acquires a phase shift equal to (provided that the filter is used

second tweeter butterworth)

, 1.4142. arctg -AT1-BT

I- I-Ј

where $ l2 4 / 4tov

oi, fl (.- cutoff frequency of the filter 15

high frequencies

It arrives at the first input of the adder 5, to the fifth input of which simultaneously with the switch of the second Electronic Switch 11, which is in the closed potential state arctg

(K nK ± itЈjLLK #kЈosiv :: 22 l, (2)

G KM1 + KmG (KM1Kfnch + KM1Kf6ch) 31p (U-90)

where Km is the transfer coefficient of the second strain gauge wash 2;

KfV - module of the transmission coefficient of the filter 15 high frequencies.

Low-pass filters 4 and high-pass 15s are selected as active, and equality is achieved at the operating frequency, then the expression

(2) can be written as

.,.,. (K ", - KMi) cos (V-90 °)

l -arctg ---------- - -K) sin ((f (90

 m 1 lv m. 1

m,

(3)

-

With a further increase in the force-induced influence in the dynamic mode, a decrease in the transfer coefficient of the strain gauge bridge 1 and an increase in the transfer coefficient of the strain gauge bridge 2 will at some point lead to an approximate equality (with a certain degree of accuracy determined by the voltage level of the operation Ucpc (Ј comparator 7 ratio) of the transfer factors

Ј.

bridges (for Ј. 3-), as a result

at the output of the voltage comparator 7, Vits has a rectangular pulse, at the front of which D-flip-flop 8 goes into a new state: at a non-inverse output, a potential of a level of a logical unit, and at an inverse output a potential of a level of logical zero. As a result, the key of the third electronic switch 12 is closed (by the level of the logical unit at the control input from the non-inverse D-flip-flop output) and connects the output

the scarlet of the unit level from the inverse output of the D-flip-flop 8, comes the oscillation UM from the output of the second tensor-resistor bridge 2.

The process of summing the oscillations in the adder 5 is shown in a vector diagram (Fig. 2b). For ease of analysis, the cut-off frequency of the low-pass filter 4 is the cut-off frequency of the high-pass filter 15 selected such that I, H4 I%, 61 / f. In this case, the total phase shift at the output of the adder 5 is equal to

the first strain gauge 1 with the fifth input of the adder 5, and the key of the fourth electronic switch 13 also closes (the level of the logical unit from the output of the second logic element HE 14 connected by the input to the inverse output of the D-flip-flop 8) and connects the output of the second strain gauge 2 to the fourth input of the adder 5. Now the oscillation and “goes to the fifth, and the oscillation

U - on the fourth inputs of the adder.

The oscillations on the first, second, and third inputs of adder 5 are formed in the same way as with a small force effect on the strain gauge bridges. The total phase shift at the output of adder 5 is equal to

 (Kv l-KM4) cos (4-900) "ft.-arctg to-- --- ynS (e

(four).

It follows from formulas (1) - (4) that the phase shift of the oscillations at the output of the adder functionally depends on the magnitude of the transmission coefficients Km, KMg of the strain gauge bridges 1 and 2, and consequently, from the measured effect. The oscillations from the output of the adder 5 arrive at the first input of the phase meter 16, to the second input of which oscillations of the output of the reference generator 3 arrive.

The force effect on the strain gauge elements leads to a change in the transfer coefficients KW1, KM; 1 strain gauge bridges 1 and 2. This causes a change in the phase shift at the output of the adder 5 and the readings of the phase meter 16 change in accordance with

with a measured value of power voz-. action The strain gauge bridge primary measuring transducers have a sufficiently large temperature error, characterized by a temperature sensitivity coefficient (TSC) and a temperature resistance coefficient (TCR) forming the strain gauge.

When used in the proposed converter, single-type strain gauge bridges with a single-frequency TCHP and a thermal-dependent resistive voltage divider, the resistors of which have TKS of the opposite sign, equal in magnitude to the DCT of the strain-resistant bridges, the phase shift (f weakly depends on the ambient temperature).

Thus, the proposed converter makes it possible to increase by 3.6 times the steepness and by 4.6 times the stability of the conversion characteristic in a wide range of temperature variations.

Claims (1)

Invention Formula A strain gauge sensor signal converter containing a reference generator, two strain gauge bridges, the input of which is simultaneously connected to the output of the reference generator, a phase meter, a high-pass filter and an adder, the first input of which is connected to the output of the high-pass filter, and the output t in order to improve the accuracy of the conversion, a low-pass filter, a comparator, a D-trigger, four electronic switches, two NOT logic elements, and a thermal-dependent 0 five 0 A tangent voltage divider, the input of which is connected to the output of the reference generator and the second input of the phase meter, while the output of the thermodependent resistive voltage divider is connected to the second input of the adder, and the input of the thermally dependent resistive voltage divider is connected to the inputs of the strain resistant bridges and the second input of the phasemeter the output is with the second input of the adder, the input of the low-pass filter is connected to the output of the first strain gauge bridge, and the output is connected to the third input of the adder, the input of the D-flip-flop is connected to the output of the comparator The inputs are connected to the outputs of the strain gauge bridges, and the non-inverted output of the D-flip-flop is connected to the control input of the first electronic switch and the input of the first logic element NOT, the output of which is connected to the control input of the second electronic switch 5, and the input the input of the first electronic switch, with the output of the first strain gauge bridge and the input of the low-pass filter, the output of the second electronic switch is connected to the fourth input of the adder, the inverse output of the D-flip-flop is connected to the controller The main input of the third electronic switch and the input of the second logical element HE, the output of which is connected to the control input of the fourth electronic switch, the output of which is connected to the fourth input of the adder, the input of the fourth electronic switch is connected to the input of the third electronic switch, with the output of the second tensor-bearing bridge and the input of the high-pass filter, and the outputs of the first and fourth electronic switches are connected to the fifth input of the adder. 0 five 0 u, 11fnch FIG. 2