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| Subject: Tacho Problems | |
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Author: Bob P |
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Date Posted: Sat, Mar 23 2013, 10:55:42 GMT In reply to: Alan Gill 's message, "Tacho Problems" on Fri, Mar 22 2013, 11:25:32 GMT Many thanks for that info Alan. I’ll meter my coils out when I next go to the airfield (presently under 100mm snow). In the mean time I’ve checked out my rev counter by driving it on the bench from a calibrated signal generator. My rev counter is an Avia Sport but on the back it has a Ducati label. It has two wires (one from the taco output of the engine and one to earth) and uses the tacho signal to power the internals (effectively it has an internal rectifier/regulator). Providing the input ac voltage is high enough (an average of around 7 volts for 1000rpm increasing to 15 volts for 8000rpm) the needle position is determined solely by the frequency of the ac input signal – for a given frequency (engine rpm) increasing the voltage further has no effect on the needle position, but if the voltage is reduced the needle drops progressively. When the signal voltage is big enough the needle should show 1000rpm at 100 hz, 2000rpm at 200hz etc. My rev counter reads around 150rpm higher than the true rpm at all speeds between 1000 and 7000 rpm, so the error is on the safe side (when the tacho reaches the max rpm red line, the engine is really 150rpm below that). So I think my low rpm readings when one of the mags is disabled must be because the tacho signal voltage drops. As a temporary fix and to give me best tacho accuracy in the plane I’ve made a little circuit to amplify the signal from the engine to a square waveform at battery voltage. Cheers Bob [ Next Thread | Previous Thread | Next Message | Previous Message ] |
| Subject | Author | Date |
| Tacho (and battery over voltage) Problems. | Bob P | Mon, Apr 22 2013, 10:29:57 GMT |