Automated measurement of frequency response of electrical networks, filters and amplifiers

Abstract

This paper describes the design, operation and use of a PC controlled automated frequency response measurement system using the standard bench-top test equipment available in undergraduate electronics laboratories. The system described employs the waveform data acquisition and processing capabilities of digital oscilloscopes to extract amplitudes (rms or peak), periods, frequencies and relative time delays of waveforms measured at the input and output terminals of a circuit under test. In combination with GPIB control of oscilloscope settings and the frequency of a signal generator, full automation of the frequency response measurement is achieved in a cost-effective manner by using a Lab View code developed. The frequency range is of the current system is 12mHz to 12MHz, more than needed for most electronic/acoustic and electromechanical systems frequency tests, and can be expanded by employing a signal generator with higher frequency range. Frequency response measurements are not unique to electronic circuits, amplifiers and filters. The measurement system described here can easily be adapted to determine the frequency response of mechanical, acoustical and other electromechanical and nonelectrical systems as long as appropriate transducers/sensors are introduced to do the required conversions from electrical to non-electrical quantities and vice versa. Being a much faster alternative to manual measurements, such automated measurements meet a need recently created by the heavy emphasis put on "design" in the electronics curriculum. In the design of analog electronic circuits, in particular those requiring a narrow range of specifications to be met, the cycle time of the test has become a critical factor in fitting a large number of redesign-and-test iterations into a time-limited laboratory session.