Methods of testing small servo mechanisms and data-transmission systems

The testing of small servo mechanisms and data-transmission systems requires the design of equipment for applying input signals of varying types and for measuring the resulting response at the output shaft. The mechanisms to be tested were all of a type in which a relatively small power was available, and the testing equipment described was specially designed to ensure observations of great accuracy, i.e. within about 2 min of arc, and to require a negligible amount of power to operate it. Direct methods of measuring response by a pen or pointer on a revolving drum were impracticable, and the basis of the equipment was the use of mirrors and light beams. Equipments are described for applying step-function signals (which represent sudden movements of the input shaft over various angles) both to servo mechanisms and data-transmission apparatus, and also for the accurate measurement of the response. A description is given of a harmonic generator which can be used to apply signals of accurate sine-wave shape, varying in amplitude from 1° to 80° and with frequencies from 0.15 to 20 c/s Methods of determining the maximum amplitude of the harmonic response and the phase lag are described. The results of tests on (a) a range-conversion servo mechanism, (b) a 2-in Magslip receiver driven by a 3-in Magslip transmitter, (c) a 3-in synchro repeater driven by a Magslip transmitter, and (d) a German 500-c/s data-transmission system are given. A special brake, designed to enable the operation of a small servo mechanism under load to be studied, is described. Methods of observing the error in response with continuous rotation of the transmitter shaft owing to irregularities of construction are given, and also methods of estimating the average error in response owing to steps of different type and amplitude.