SU892713A1 - Frequency converter for strain-gauges - Google Patents

Description

(54) FREQUENCY CONVERTER FOR HEAT SENSORS

I

The invention relates to digital electrical measuring technology and can be used in measurement systems and monitoring and control systems using strain gauges of various physical quantities with a bridge measuring circuit.

A frequency converter for strain gauges is known, which contains a voltage source, a strain gauge, connected in series to its measuring diagonal DC differential current amplifier, integrator, and comparison unit ij

The disadvantage of this converter is the low conversion accuracy due to the instability of the parameters of the integrator, the differential DC amplifier and the comparator, the input is searched in the direct signal conversion path from the output of the measuring diagonal of the strain gauge.

A frequency converter for strain gauges is also known, which contains a power source of the strain gauge connected to its power diagonal, the first key whose output is the power switch; It is connected to the first vertex of the measuring diagonal of the tensomer, and the integrator, implemented on an operational amplifier with a capacitive negative feedback, whose output is connected to the input of the comparator unit, the output of which is connected to the input of the pulse former 2.

The disadvantage of the known converter is low accuracy.

15, which is due to the influence on its number of parameters of the device elements.

The purpose of the invention is to improve the accuracy of the conversion.

20

The goal is achieved by the fact that the frequency converter for strain gauges, containing the power supply of the strain gauge, is connected to its power diagonal, and the first key, the output of which is connected to the first vertex of the measuring diagonal of the strain gauge, and the integrator, made on an operational amplifier with a capacitive negative feedback A capacitor is connected to the input of the comparison unit, the output of which is connected to the input of the pulse shaper, a capacitor is introduced through the second and third keys connected to the diagonal and the fourth key and the first resistor connected to the inverting input of the integrator, the first key input connected to the connection point of the capacitor and the second key, the first vertex of the measuring diagonal of the tensometer connecting the second resistor to the inverting input of the integrator, the non-inverting input of the integrator connected to the second vertex -, by the measuring diagonal bus of the bridge, the control inputs of the first and fourth keys are connected to the first output of the pulse shaper, and the control inputs of volt cerned and the third key - to its second output. FIG. 1 shows a functional electrical circuit of a frequency converter for strain gauges; in fig. 2 - time diagrams. The device contains a power source 1, a strain gauge 2, an ind-integrator 3, a comparison unit 4, keys 5,6,7 and 8, a capacitor 9, resistors 10 and 1, and a pulse shaper 12, the power source 1 being connected to the diagonal power of the strain gauge 2 , the first vertex of the measuring diagonal of which is connected to the output of the key 5, the output of the integrator 3 is connected to the input of the comparator unit 4, the non-inverting input of the integrator 3 is connected to the second vertex of the measuring diagonal of the strain gauge 2, the first of which is connected to the first vertex of the diagonal 6 laying the capacitor 9 and the key input 5, and the second vertex of the power diagonal by means of the key 7 connect with the second plate of the capacitor 9 and the input of the key 8, the output of which through the resistor 10 is connected to the integrator input, which is connected to the first vertex of the measuring diagonal of the tensometer 2 through a resistor 10 The output of the comparison unit 34 is connected to the input of the pulse driver 12, the first output of which is connected to the control inputs of the keys 5 and 8, and the second output is connected to the control inputs of the keys 6 and 7. FIG. Figure 2 shows timing diagrams explaining the operation of the circuit, at the output of the integrator 3 (Ug), at the output of the comparison unit 4 (Uj). At the outputs of the imaging device 12 (Uo and U2) and on the capacitor 9 (U). The device works as follows. At time t. the output voltage of the integrator 3 reaches zero level, the comparison unit 4 is activated and, on its signal, the shaper 52 opens the previously closed keys 5 and 8, and at the time t / f closes the keys 6 and 7 connecting the capacitor 9 to the diagonal power supply of the strain gauge 2. K time tj charge on the reference capacitor 9 will be equal to where Uy, is the voltage of the power source; Cd is the capacitance of capacitor 9. At this time, keys 6 and 7 are depleted by the signal from driver 12, keys 5 and 8 close at time t, and capacitor 9 begins to discharge through resistors 10 and 1}. In this case, the voltage at the output of the integrator 3 begins to increase. At the same time, the inverter has an input (tm) of integrator 3, made on the basis of an operational amplifier with a capacitive negative feedback and with a parallel H1 1 channel of the drift zero sampling channel, and in one of the top tires of the measuring diagonal (V.1 ) The tensome bridge maintains equality of potentials. The potential difference between the second vertex of the measuring diagonal of the tensome bridge (T.k) and the inverting input of the integrator operational amplifier (t) is equal to the voltage unbalance of the tensome bridge 2. (2) and gu Jupe n, AB where g is the imbalance of the tensome 2.

As a result, at the end of the discharge of the capacitor 9, the voltage at the output of the integrator 3 begins to decrease, at time t "reaches zero level, and the recovery cycle will repeat.

In this case, the volt-second signal area from the capacitor 9 is equal to the volt-second voltage area of the imbalance 2 unbalance during the conversion cycle Tu,

 P / IM ITX (3)

De 1. The current flowing through the resistor 11 from the discharge of the capacitor 9;

1, is the resistance value of resistor 11;

tp is the discharge time of the reference capacitor 9 .. On the other hand

Ji ,, pat - uv, co. ()

Substituting (4) into (3) and solving equation (4) with respect to f -f, we obtain the function

.BUT . ,

(five)

x

where the output frequency of the transducer.

The control pulses, closing the keys 5,8 and 6,7 are separated in time, which excludes the possibility of simultaneous closing of the keys 5,6 and 7,8.

As can be seen from (5), the minimum number of parameters of the circuit elements is included in the conversion function.

Thus, due to the distinctive features of the proposed frequency converter, the conversion accuracy is improved.

Claims (2)

Invention Formula A frequency converter for strain gauges containing the power supply of the strain gauge connected to its power diagonal, and the first switch, the output of which is connected to the first vertex of the measuring diagonal of the strain gauge, and the integrator performed on an operational amplifier with a capacitive negative feedback, the output of which is connected to the input of the comparator unit, the output of which is connected to the input of the pulse former, characterized in that, in order to increase the conversion accuracy, a capacitor is inserted into it through the second and third keys connected to the diagonal power supply of the strain gauge, and through the fourth key and the first resistor connected to the inverting input of the integrator, and the input of the first key is connected to the point connecting the capacitor and the second switch, the first vertex of the measuring diagonal of the strain gauge is connected via a second resistor and the inverting input of the integrator, non-inverted integrator input is connected to the second tip of the measuring diagonal: the strain gauge, the control inputs of the first and fourth keys are connected to the first output of the pulse shaper, and the control inputs of the first and fourth keys are connected to the first output of the pulse shaper, and second and third keys - to his second exit. Sources of information taken into account in the examination of 1. March AI A.I and others. Converters of electrical parameters for control and measurement systems. M., Energie, 1976. 2. USSR author's certificate No. 572644, cl. G 01 B 7/16, 1975 (prototype). / GU