EXPRESS METHOD OF EVALUATION OF SPEED OF COMPLEX MEASURING SYSTEMS
10.33815/2313-4763.2021.2.25.075-082
Abstract
When developing a complex measuring system, it is often necessary to evaluate its dynamic parameters in order to determine the speed of response, which is especially important when creating automatic measuring instruments. Moreover, such structures often include voltage-controlled amplifiers, which actually carry out the operation of signal multiplication. In order to apply the structures used in the theory of automatic control (TAU), such elements are replaced by adders of logarithms with subsequent potentiation. To linearize the operations of logarithm and potentiation, they are approximately represented as operations of subtraction and addition of linear functions. Other non-linear operations of the measuring units are expressed in a similar way. The resulting structures are presented as TAU circuits with the subsequent compilation of their transfer functions, on the basis of which the transient response of the system as a whole is determined. As an example of the application of the above method, a circuit for measuring the capacitance of varicaps based on a capacitive divider with spatial separation of measurement channels is considered, containing a high-frequency generator, a capacitive divider, which includes a measured varicap, a controlled amplifier, two measurement channels containing high-frequency amplifiers and detectors, subtractor, comparison device, reference voltage source. One of the measurement channels is covered by negative feedback, the second contains a subtractor, due to which a signal proportional to the measured capacitance is generated at its output. It is shown how the speed of the given circuit can be calculated with an abrupt change in the bias voltage supplied to the measured varicap through the decoupling element. The proposed method for the approximate calculation of the speed of the measuring systems is quite simple and effective and makes it possible to significantly simplify the determination of the dynamic parameters of not only measuring, but also control systems containing links that carry out the operations of multiplying or dividing signals.
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