SU711494A1 - Arrangement for measuring capacitor capacitance - Google Patents

Description

The device relates to the field of measurement technology and can be used in devices for measuring capacitance.

A device [1] for measuring capacitance is known, which comprises a self-oscillator with a measured capacitance, a reference self-oscillator, shapers, valves, a meter of periods and difference of periods, consisting of recalculation schemes of a larger and shorter period, a trigger for coincidence matching, a pulse generator, a reverse counter, divider by two. However, this device has a low accuracy of measurement due to the occurrence in time of the frequency difference between the reference and measuring generators.

A device [21 for measuring capacitance of capacitors is known, comprising a measuring generator, the input of which is connected via a switch to a reference and measured capacitors, the outputs of the measuring 25 generator are connected to the control inputs of the key, the other input of which is connected to the output of a pulse crystal oscillator, a control unit ,, pulse counter,. adders. thirty

However, this device has low measurement accuracy at low capacitance values (less than 10 pF due to the insertion capacitance of the switches).

• The aim of the invention is to improve the accuracy of measuring capacitors.

This goal is achieved by the fact that in a device for measuring capacitance of capacitors containing a measuring generator with an oscillatory circuit, the output of which is connected to the clamps for connecting the measured capacitor, a pulsed crystal oscillator, pulse shaper, counter, reversible counters, I elements, and a control unit, first, the second, third and fourth outputs of which are connected to the control inputs of AND elements, the fifth output is connected to the input of the `` Setting 0 '' reverse counters, parallel to the oscillatory the circuit of the measuring generator includes a switch, and the output of the measuring generator through a pulse former is connected to the input of the counter, the output of which is connected to one of the inputs of the control unit and to one of the inputs of the first element And, the other input of which is connected to the output of the pulse crystal oscillator and with one of the inputs of the third and fourth elements And, and one of the inputs of the second element And is connected to the output of the pulse shaper, the other input of the second element And is connected to the zero output of the first reversal meter, with other inputs of the third and fourth ^ cements AND and the control unit, you-. the moves of the first and second elements And, respectively, are connected to the input of addition and subtraction of the first rever At the end of the subtraction from the reversible counter 7, a signal of zero state is received, which closes the elements 10 and 11 And, while supplying a signal to the control unit 1. In this case, the control unit 1 transfers the device to the second period of operation. In this case, switch 5 is closed and switch 4 is opened. Capacitance Co is connected to the circuit. + C * The operation of the circuit is further similar to that described10. First, the number of this counter will be written to the reversible counter, and the outputs of the third and fourth elements AND are connected respectively to the addition and subtraction inputs of the second reversible counter, the sixth output of the control unit is connected to the addition input of the first reversible counter.

The drawing shows a functional electrical diagram of the device.

The device comprises a control unit 1, a measuring generator 2, a pulsed crystal oscillator 3, switches 4 and 5, a counter 6, reversible counters 7 and 8, elements 9, 10, 11, 12 And, a pulse shaper 13.

The device has two periods of operation. In the first period, switch 4 closes and switch 5 opens. A capacitance C _h5 + С _о + С _{х is} connected to the oscillating circuit, where С ^ ₅ is the capacitance of switch 5. Oscillations from measuring generator 2 are supplied through pulse former 13 counter 6, counter b, together with the control unit 1, open the element 9 And, which passes pulses from the pulse crystal oscillator 3 to the 'reverse counter 7. Through K pulses, the counter 6 closes the element 9 And and gives a signal to the control unit 1. In this case, the counter 7 will be recorded number _x ravkt Noe ί ->

.. ^υ . where K is the coefficient of recalculation of the counter 6, Τ _υ is the oscillation period of the pulsed quartz generator. From the control unit 1, the unit enters the reverse counter 7. jq The control unit turns off the element 9 AND and connects the elements 10 and 11 AND. In this case, the number from counter 7 starts to be subtracted to zero by pulses with a period. Subtraction time will be equal

Kto

From the control unit 1, an additional unit is supplied to the reverse counter 7.

The control unit 1 disables the element-9 And connects the elements 10 and 12 AND.

The time to subtract the number from the reverse counter 7 will be equal to

From the counter 8, a number equal to

At the end of both periods of work in the counter 8 will be recorded number

However, at the same time, element 11 AND will be opened ₍ and a number will be written in the counter 8:

Thus, if we select the ratio CT _ o 'equal to 1, then a number equal to the value of the capacitance will be recorded in the 41CH counter-clock counter 8.

Claims (2)

1. USSR author's certificate No. 310198, cl. G 01, R 27/26, 1968 (equivalent). 2. „Measuring equipment 5, 1975, p. 16 (prototype).