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Tachogenerator Interface

As most gas turbines use either their generator or a dedicated tachogenerator to give gas-generator or shaft rotational speed (via ouput voltage or frequency) I needed an interface that could cope with anything an engine might present.

The circuit I eventually settled on is pretty much a saturating-AGC, it has very good performance with voltages ranging from 50mV to 100V and frequencies from under 1Hz to over 200Hz.

The diode clamp on the input is a neat little construct that provides excellent clamping while only presenting the capacitance of a single zener/silicon diode combination. It's low-leakage as well.

Please feel free to use this circuit in your own hardware, it was very kindly designed by an analog wizard at my place of work.

PSPICE Schematic of the tacho interface

60mV 1Hz input test

3V 80Hz input test

PSPICE File Package: DOWNLOAD