Transfer function measuring and recording system

THE SYSTEM DESCRIBED gives a polar plot of the transfer functions of industrial processes, process controllers, and instrument servomechanisms. Included in the system is an accurate mechanical signal generator which produces pneumatic, electric, and motion sine waves having a frequency range of 1/30 to 720 cycles per minute. A data sampling technique is employed which by-passes the need for having recorders with a dynamic response considerably better than the system under test. Furthermore, the Nyquist plot is recorded directly on a single sheet of paper thus simplifying the data reduction, handling, and storage problem. As the transfer function may be studied while the test is in progress, the operator is assured that he will not miss any significant points of the plot.