912ULS tacho and mag drop puzzles

No difference at all with a 220R I'm afraid. I think the 200rpm error is just calibration creep, the tacho is quite a few years old. A tiny tweak on the calibration screw fixed it.

Mike

Well, try that 220r with the Tach installed back in the plane and see if the reading corrects.

I've now put the tach back in the plane and injected the transformer "calibration" signal into the wiring. Both the tach and the MGL behave perfectly (without the resistor). The MGL was stable to one digit. I think that eliminates everything except the signal produced by the Rotax. I should be able to run the engine in a few days.

Incidentally in my Kitfox i had the same setup, a 912 with a Rotax tach and an MGL, and it gave no problems without a resistor.

Mike Wylde wrote:

I've now put the tach back in the plane and injected the transformer "calibration" signal into the wiring. Both the tach and the MGL behave perfectly (without the resistor). The MGL was stable to one digit. I think that eliminates everything except the signal produced by the Rotax. I should be able to run the engine in a few days.

Incidentally in my Kitfox i had the same setup, a 912 with a Rotax tach and an MGL, and it gave no problems without a resistor.

OK - having read the entire thread now, I gotta ask:  You've heard the saying "A man with two clocks never knows what time it is", right?  So why would you want two tachometers in the plane?  If the MGL is working correctly for you, why not save the weight and trouble, and get rid of the duplicate tach?

The MGL-E1 is there to give me 4 EGTs and 2 CHTs. It also has a small digital rpm display that you can read if you get close to the panel and it's not too sunny. Normally I wouldn't be using it.