SU752175A1 - Voltage and resistance meter - Google Patents

Description

The invention relates to electrical measuring equipment and can be used in the measurement of resistance, direct current voltage or difference between two measured voltage potentiometrically (compensation) method. Potentiometers (compensators) are known that provide measurement of DC voltages and direct current resistances, which contain reference circuits, power sources of reference circuits, and an autocompensator 1.. The disadvantage of these potentiometers is that their functionality is limited, their resistance is measured indirectly and is associated with a number of intermediate calculations. Voltage and resistance meters are also known, which contain a single bridge with a voltage source connected to the inverter input input of the operational amplifier. In the feedback circuit of the operational amplifier with a series feedback voltage, the conductivities are turned on, each of which can be performed on a binary-decimal or other code and. The disadvantage of these gauges is also in limited functionality, since they cannot be used as direct-measure resistance meters. The closest technical solution to the present invention is a device for measuring voltages and resistances, which is a variable-current potentiometer and contains a source, a reference voltage, an amplifier, a voltage divider, a switching device and an autocompensator | 3. The disadvantage of this device is the impossibility of using it as a resistance meter with direct reading. In addition, due to the inadequacy of the input resistance, high requirements are imposed on the source of compensating voltage, i.e. it must have a very small output resistance (in thousand of ohms). The purpose of the invention is to expand the functionality of the meter by simultaneously measuring two voltages or resistances and the difference between them.

The goal is achieved by the fact that a voltage divider connected to the output of the operational amplifier and to the first input of the meter, a switch and an adjustable voltage divider with a constant input resistance are included in the voltage and resistance meter, containing a source of compensating voltage. A switch connected via parallel to the aforementioned voltage divider, the output of which is connected to another input of the switch, and the second input of the meter is connected to the control terminals uemogo voltage divider.

FIG. Figure 1 shows a diagram of the proposed voltage and resistance meter; in fig. 2 - measured object.

The meter contains a compensating voltage source 1, parallel to which a voltage divider 2 is connected, connected to the output 3 of the operational amplifier 4 and to the first input 5 of the meter. An adjustable voltage divider 7 with a constant input resistance is switched on via the switch b parallel to the voltage divider 2. The second input 8 of the meter is connected to the pins of the adjustable divider 7. The device also contains fixed contacts 9, 10 of the switch b, exemplary resistance 11, measured resistance 1 voltage source 13.

The device works as follows.

A switch b connects a divider with a constant input impedance 7 either to the output of divider 2 (position 9) or to the output of operational amplifier 4 (position 10). In position 9 of switch 6, divider 7 is a shunt that has conductivity for divider 2.

The measurement of the voltage difference is carried out as follows.

At position 10 of switch 6, the circuit is a two-row potentiometer in which one unknown measured voltage is connected via an equilibrium indicator to the terminals of the first input 5 of the meter and is balanced by divider 2, and the second unknown measured voltage is connected to the terminals of the second input 8 is balanced by a divider 7 with a constant input impedance. The determination of the percentage difference of the measured stresses occurs in the following way.

 At position 9 of switch 6, the larger measured voltage is connected to the terminals of the first input 5 of the meter and is balanced by the divider 2, and the lower measured voltage is connected to the terminals of the second input 8 of the meter and balanced by the voltage divider 7 with a constant input impedance. Denoting the division factor of divider 2 (taking into account the shunting effect of divider 7) through Kd., And the division factor of divider 7 through Kd, we obtain the following relations

Ux, Kd, E, Ux Kd Kd, - E,

where U is the larger measured voltage;

hp is the smaller measured voltage.

The relative difference between the two measured voltages is determined by the level

Ux,

-ts ---)

On the reading device for each decade, the addition to 9 (if each decade consists of 10 steps or up to 8 (if each decade consists of 9 steps), we obtain the percentage potentiometer in this way. In younger cases, the addition is performed to 10 and 9, respectively.

Measurement of resistance with a direct reading of the result according to the indications of the decades of the divider 7 is carried out in the following way.

Exemplary 11 (R) and measured 12 (RX) resistances are connected in series and powered from a voltage source 13 (E). In this case, the switch 6 is set to position 9. For measurements, the reference voltage is chosen to be round the nominal value, i.e. equal to 10, where n is a positive or negative integer. The voltage drop on the reference resistance 11 is balanced by the divider 2, and the voltage drop on the measured resistance 12 is balanced by the divider 7. Denoting the current through the measured and reference resistance as J, we get

WITH)

 ZN, EKd,

and

Xi

UXj 3h E Kd. (5) Since, by condition, Kc has a circular nominal value, Ux directly indicates the value of the measured resistance.

Despite the fact that the current CJ is non-circular and the voltage drop Uy is also non-circular, the result of measuring RX is directly expressed by KdijL (i.e. counting over decade divider 7), since it follows from (4) and (5) that

Claims (3)

3R EKd, G-RX from where Rj (Rj Thus, the result of the measurement is directly measured by the decade of the divider 7 (RU is expressed by)). In addition, the circuit (figure 1) is also a comparator of equal resistance, allowing gadium determine the percentage difference between the large and smaller measurable resistances. This follows directly from equation (3), which is applied to measure resistance, taking into account equations (4) and (5), as (i-Ke,) - - (i-Kd,). In equation (7), under R |, more is implied, and under R y is the smallest of the comparable uniform resistances. Thus, the proposed invention is a simple in structure and constructive implementation of a multifunctional measuring device capable of replacing a whole range of other measuring tools in one device, namely a high-precision potentiometer, a single and double bridges for measuring resistance, voltage comparator, resistance comparator. Claims A voltage and resistance meter containing a source of compensating voltage, in parallel with which, a voltage divider connected to the output of the operational amplifier and to the first input of the meter, is different in that in order to extend the functionality by simultaneously measuring two voltages or resistances and the difference between them, a switch and an adjustable voltage divider with a constant input resistance are included in it, connected through a parallel switch to the aforementioned voltage divider, the output of which is connected to another input of the switch, and the second input of the meter is connected to the terminals of the adjustable voltage divider. Sources of information taken into account in the examination 1. Netrebenko K.A. Digital voltage dividers, M., Energie, 1970, p. 30-31. 2..Ornatsky P.P. Automatic measurements and instruments. Kiev, Higher School, 1971, p. 123. 3. Alexandrov B.C. and Pr Nishnikov V.A. Instruments for measuring small DC voltages and currents. L., Energie, 1971, p. 25