Published:2009/6/19 3:02:00 Author:May | From:SeekIC
Control and process equipment often require the indication of frequency (speed or rate) of linear or rotary mechanical movement. Motion can be detected using various pulse-generating pickups and proximity detectors that output ac or dc pulsed signals.This industrial converter can serve in a wide variety of applications. The circuit operates around a quad-FET input op amp and is designed to be selfcontained or run from a bipolar supply. The in-put signal of dc pulses or ac waveforms is applied to R2.Amplifier 1, which acts as a Schmitt trigger, supplies a squarewave output of fixed amplitude to C4. Resistor R3 and capacitor C6 filter out input noise, and R4 and R5 determine the switching levels, and Zener diode 23 sets the amplitude.Amplifier 2 gives a fixed-duration pulse on the positive transition of C4, with a time constant set by C4 and R6 and the switching level set by R7 and R8. Resistor R9 and Zener diode 22 fix the am-plitude of the pulses and amplifier 3 integrates them via R10 and C5. Diode D6 blocks negative inte-gration and R11 discharges C5 with a long-time constant.Hence, the dc output of amplifier 3 is proportional to the frequency applied to the input. Amplifier 4 inverts and buffers the negative output of amplifier 3 and provides amplitude adjustment voltage.The complete circuit is linear and sufficiently accurate providing that C4 is chosen to give a pulse duration less than the maximum input frequency and that R11 > R10.
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