GB732532A - Improvements in or relating to frequency responsive speed indicators particularly tachometers - Google Patents

Abstract

732,532. Frequency measurements. SANGAMO WESTON, Ltd. July 11, 1952 [July 19, 1951], No. 17189/51. Class 37. [Also in Group XXXVIII] A high-speed tachometer comprises an A.C. generator driven by a shaft to produce frequencies proportional to the shaft speeds which are converted by modulators and filters to frequencies showing a greater percentage frequency change with shaft speed change than do the output frequencies of the generator; such frequencies being amplified to operate a vibratory armature relay which charges and discharges a condenser to produce an average current in a ratiometer coil which is a function of the relay operating frequency, whereby the ratiometer displays the shaft rotational speed on an expanded scale. A single-phase tachometer generator 10 is driven from the shaft 11 of a jet engine at e.g. 7000-8000 r.p.m., and the output at e.g. 700-800 c.p.s. passes through a high-pass filter 13 of e.g. 650 c/s. cut-off, to a modulator 14 where the input frequency is combined with a constant frequency of e.g. 650 c/s. from e.g. a tuning fork 15, and the constant frequency component and the unwanted sideband are removed from the output by a lowpass filter 16 of e.g..150 c/s. cut-off. The resultant output frequency varying over a range of frequency (e.g. 50 to 150 c/s.) having a greater percentage rate of change with respect to shaft speed than the input frequency from the tachometer generator, is amplified at 17 and energizes a vibrating reed relay 18 whose vibratory contacts 19, 22 when closed charge a condenser 21 from a battery 23 through a resistor 24, and whose contacts 19, 20 when closed discharge the condenser through coil 26 of a moving-coil ratiometer whose other coil 27 is continuously connected to the battery through a resistor 28. The average current from the condenser is proportional to the frequency energizing the relay so that the indicator effectively indicates the shaft speed over an expanded scale range. The entire speed range, e.g. 0-8000 r.p.m., may be indicated by a moving-coil instrument 30 energized by the rectified voltage output of the tachometer generator. Specification 682,534, [Group XXXVIII], is referred to.