SU789895A1 - Apparatus for measuring resistance ratio - Google Patents

Description

one

The invention relates to instrumentation technology and can be used to create instruments for checking the relationship of resistances and resistors.

A digital ohmmeter is known, which contains a voltage divider formed by etshonny and measurable resistors and connected to a reference voltage source, and an integrator, the inputs of which through a switch are connected to the corresponding points of the divider. ONweTp is based on the determination of time intervals proportional to the values of the measured and reference resistance, and their subsequent division

The disadvantage of the ohmmeter is low speed due to the fact that the measurements are carried out in two cycles with the memorization of the results. This also leads to errors in the measurements.

The closest technical solution to the proposed is a digital ohmmeter containing a divider formed by a reference and measurable resistors, three comparators, the first inputs of which are connected between.

the second input of the first comparator is connected to the midpoint of the divider, the second input of the second comparator is connected to the grounded terminal of the measured resistor, the second output of the third comparator is connected to the source of the reference voltage and

10 with a reference resistor, a switch connected in parallel with the reference resistor, the outputs of the first and second comparators are connected via the first driver of the strobe and the first

15 a selector with a first input of a digital splitter, outputs of the first and third comparators are connected via a second selector with a second input of a digital splitter, and a reference frequency generator, the output of which is connected to both selectors. An ohmmeter compares the voltage from a generator of a linearly varying voltage with a voltage drop across

25 reference and measurable resistors with subsequent conversion of these voltages into time intervals, then into a digital code, and finally, digital division is performed i

3Q values

Comparators work in. the moments of the passage of the linearly increasing voltage across the zero potential; the equality of the linearly increasing voltage across the measured resistor (and ,,) and the equality of the linearly increasing voltage to the voltage (DO + and) on the divider.

A disadvantage of the known technical solution is that the fixation of each of the three moments of operation of the comparators is carried out with certain errors, the operation of the digital division of the obtained values of the two resistances also has errors. In addition, the well-known ohmmeter is complicated in construction.

The purpose of the invention is to improve the accuracy and simplify the design.

The goal is achieved by having two comparators, the first inputs of which are interconnected, and the second inputs connected to the midpoint of the splitter and the measured resistor, respectively, to a device for measuring the ratio of resistance, which contains a divider formed by the reference and measurable resistors. , DC source, counter, entered integrator, temporary gate driver, whose inputs are connected to the comparators' outputs, output - to the control input of the counter, the counting input of which connected to the output of the reference frequency generator, the integrator input is connected to the midpoint of the divider, the output to the first inputs of the comparators, the output of the DC source is connected to the measured resistor, the second, the output of the reference resistor is connected to ground.

The drawing shows a block diagram of the proposed device.

The device contains a reference resistor 1, a measuring resistor 2, an integrator 3, comparators 4 and 5, a temporary gate shaper b, a counter 7, a reference frequency generator 8, a DC source 9.

The device works as follows.

With the passage of current through the divider on the reference resistor 1, a voltage drop of LKE / a is formed on the measuring resistor 2 - 3R) ;. The voltage SQd is fed to the input of the integrator 3, at the output of which we have a linearly increasing voltage

Zke t

where t is constant time

integrator 3.

On. the inputs of the comparator 5 are the voltage of the ZR from the midpoint of the wake ti ti tel and voltage

from the exit

(t

integrator 3.

at the moment of coincidence of these two voltages, comparator 5 is activated. This moment can be defined as

-1R - t, -ZKe

where t t.

Thus, at time t t, the signal arriving at shaper b from comparator 5 opens the temporary gate and the counter 7 begins to be filled with pulses of the reference frequency generator 8. Comparator 4 is triggered at the time of voltage matching.

Las

to

(Rg + R)

t

those. the second match happens at the moment

. (R9 +) –d –i R,

The signal received at this moment on the former by the comparator 4 closes the temporary gate and stops counting.

The filling of the counter 7 takes place during the time interval

/. - (Ra + RX) -. (V iHL

o DR

thirty -

When t is selected

h 1 - Ra

Consequently, the counter 7 records a number proportional to the desired ratio. Moreover, the measurement accuracy does not depend on the stability and internal resistance of the direct current source and the converter circuit.

At the output of the former, gates are formed, the width of which is proportional to the desired relation, therefore there is no need to memorize and then divide the values proportional to the individual R and Rg. This improves measurement accuracy and speed.

Claims (2)

1. USSR author's certificate  586402, cl. G 01 R 27/00, 19.11.75. 2. USSR author's certificate No. 602882, cl. G 01 R 27/00, 01.10.75 (prototype).