ELECTRONIC AUTOMATIC SUMMING POTENTIOMETER

N. V. Podbornov, V. K. Skripchenko, V. N. Titov

(Presented by the scientific seminar of the Faculty of Physics and Technology)

In continuous automatic monitoring of certain production processes, it is necessary to measure two or several electromotive forces produced by sensors with different characteristics, followed by summation of the measurement results and recording of the sum on chart paper. Such a case occurs, for example, in determining and recording the instantaneous values of the sum of two streams entering a chemical reaction apparatus.

Below is a description of an instrument intended for continuous automatic recording of the acidity of a solution by adding the readings of two sensors according to the proposed method [1]. The instrument performs compensation measurement of the emf in each channel, with registration of the total value of the readings of both channels.

Fig. 1. Schematic diagram of the instrument.
1 — stabilized power supply for the measuring circuit; 2 — electronic amplifier; 3 — reversible motor.

The summing potentiometer is constructed on the basis of the ÉPP-26M1 electronic automatic potentiometer and assemblies of standard automatic potentiometers. The schematic diagram of the instrument is shown in the figure.

Summation is carried out on the principle of using a two-rheostat bridge [2].

The measuring circuit of the first channel has the measuring rheostat \(R_{p1}\) and the rheostat \(R_{p2}\), which performs the function of the zero-shift rheostat.

The zero-shift rheostat \(R_{p2}\) and the rheostat of the compensating measuring circuit of the second channel \(R_{p3}\) are paired, and the sliders of the rheostats are moved by the reversible motor of the second channel circuit.

Thus, the reading of the emf of the sensor of the first channel, as a result of shifting the electrical zero of the first compensating circuit by rheostat \(R_{p2}\), is made from the point that corresponds to the algebraic value of the quantity measured by the second channel. The position of the slider of rheostat \(R_{p1}\) corresponds to the summed value of the sensor readings. The scale of the measuring circuits is regulated, respectively, by rheostats \(R_n\) and \(R_b\), which makes it possible to use sensors having different characteristics. The instrument has one common scale with two pointers, one of which indicates the value of the quantity delivered by the first sensor, while the other indicates the summed value of the measured quantities. The summed value is recorded on chart paper. The origin of the reading is shifted over the entire scale by the paired rheostat \(R_e, R_{p2}\) for the first channel and by rheostat \(R_{p3}\) for the second channel.

The measuring circuit is powered from a stabilized power supply.

All units are mounted in the housing of an EPP-26M1.

Laboratory tests established that the reduced relative error of the instrument does not exceed 1%. When the instrument supply voltage is changed by \(\pm 10\%\) from nominal, the error of the readings does not exceed the above value.

REFERENCES

1. N. V. Podbornov, V. N. Titov. Method for measuring the pH of solutions. Author’s certificate No. 161955 of October 13, 1962.

2. N. A. Pikulev. Summing devices based on units of series automatic potentiometers. Priborostroenie, No. 7, 1964.