SU405078A1 - DIGITAL RESISTANCE METER - Google Patents

Description

I

This invention relates to the field of digital electrical engineering.

Digital resistivity meters are known, comprising a measuring circuit of current-generating and measurable resistances, a comparison device, a sweep voltage generator, a driver, and a digital time interval meter.

However, these meters use two comparison devices, two sweep voltage generators, one of which is switched, and two power sources separately for the measuring circuit and for the sweep generators. In addition, these meters have insufficient measurement accuracy due to the effects of instability of the power supply, switching elements and uncompensated drift of the comparison devices.

In the proposed meter, the sweep voltage generator is designed as an active voltage divider, to the midpoint of which a passive integrating RC circuit is connected, the output of this circuit is connected to one of the inputs of the comparison device, the second input of which is connected to the midpoint of the measuring circuit, and connected through a driver with a digital meter of time intervals and through a push-pull amplifier with a measuring circuit

and a sweep voltage generator. This simplifies the circuit and increases the measurement accuracy. FIG. shows the diagram of the meter where:

1-measuring circuit of the current-setting resistor 2 and the measured resistor 3 (3-- parasitic capacitance of the resistor 3); 4 is a comparison device; 5 - push-pull amplifier; 6 - active divider resistors 7 and 8;

9 - passive integrating C-chain on elements 10 and 11; 12 - shaper; 13 - digital time interval meter.

FIG. 2 is a timing diagram illustrating the operation of the meter (a -

voltage at the midpoint of the measuring circuit, b - sweep voltage, a - distortion of the voltage fronts due to the parasitic capacitance of the measured resistor and the nonideality of the push-pull amplifier).

The device works as follows. In the initial state, the containers 3 and 11 are charged with the voltage of a certain polarity, coming from the output of the push-pull amplifier 5; since the starting impulse

t is on an arbitrary part of the charge cycle, this first cycle is idle and shaper 12 is not fixed. At the time of equality of the voltages at the inputs of the device 4 comparison, it works and

switches the polarity of the voltage at the output of the push-pull amplifier; at the same time meter 13 fixes the beginning of the first measuring cycle. Voltage - from the output of the amplifier 5 is fed to the measuring circuit 1 and to the sweep voltage generator.

The transient process in the measuring circuit ends for a time much shorter than the time constant / C-circuit, therefore at the moment of subsequent comparison of the voltages at the inputs of the device 4, the voltage at the midpoint of the measuring circuit almost reaches the set value. The ratio of the shoulders of the divider 6 is chosen to be 1: 1 from the condition of compensating for the nonlinearity of the divider formed by resistors 2 and 3. The moment of equal voltage at the midpoint of the measuring circuit and the sweep voltage at the output of the C circuit is fixed by the imaging unit 12 as the end of the first measuring cycle. Similarly, the time intervals of the subsequent measuring cycles are formed. A digital time interval meter measures them by a counting method — by accumulating counting pulses at a given number of intervals, and if necessary using averaging, i.e., reducing to one-odM interval.

A feature of the circuit is the use of only one comparison device.

and one bi-polar sweep voltage source, which allows to simplify the circuit and at the same time improve the measurement accuracy by eliminating the influence of the drift of the comparing device, the effect of the switching elements in the measuring circuit and the instability of the supply voltages.

Subject invention

A digital resistance meter containing a measuring circuit from a current-carrying and measurable resistance, a comparison device, a sweep voltage generator, a driver and a digital time interval meter, characterized in that, in order to simplify the circuit and improve the measurement accuracy, the sweep voltage generator is the active divider of the voltage, the midpoint of which is connected passively integrating, / C-circuit, the output of this circuit is connected to one of the inputs of the comparison device, Torah input of which is connected to the midpoint of the measuring circuit, and an output driver connected through a digital meter intervals of time and through a push-pull amplifier - a measuring

chain and generator sweep voltage.