EXPERIMENTAL STUDIES OF INFORMATION SIGNAL-TO-RESISTANCE CONVERTER FOR AUTOMATIC CONTROL SYSTEM

Abstract

Potentiometric sensors are widely used in the construction of automatic and automated process control systems. In potentiometric sensors, resistance is the output signal and its magnitudes depend on the magnitude of the input signal. voltage, current, digital code, angle of rotation, displacement or other signal is usually used as the input signal. In practice, the task of simulating of the signal which coming from the built-in potentiometric sensor is often appeared. An additional potentiometric sensor can be used to simulate the signal of the built-in sensor that allows setting the required resistance magnitude by changing any external parameter.
 The model of the voltage-to-resistance converter is made. This model allows simulating the potentiometric state sensor of the controlled system. The experimental determination of its transfer characteristic at different ambient temperatures is carried out. This model is based on a two-channel conversion circuit, which includes a source of optical radiation and two photoresistors optically connected to it. One of photoresistors is connected to a current stabilizer, while the voltage on it is analyzed by a tracking circuit that changes the brightness of the optical radiation source according to the magnitude of the control voltage. The transfer characteristic of the converter in the initial section has an insensitivity zone, following by a rectilinear section. Within the insensitivity zone, a change in input voltage does not change the output resistance. The magnitude of the insensitivity zone is determined by the maximum voltage on the incandescent lamp that determines its brightness, as well as the minimum possible resistance of the using illuminated photoresistor. Within the rectilinear section, the output resistance of the converter is linearly related to the magnitude of the input voltage. The conversion error does not exceed 0.6 % at an ambient temperature of 20° C. When the temperature decreases to -20° С, the conversion error increases to 7 %, which is due to differences in temperature errors of the photoresistors using in the model.