MGL Avionics User Forum

I'm running a LYcoming O-320D2B (Bendix mags) and using the magneto spark-counting feature to determine engine RPM. It works fine on the ground, but as I fly and increase speed to get RPM near 2700, the RPM counter starts intermittently jumping to 3300 and back.

I have tried, endlessly, adjusting the sensitivity rheostats. Unfortunately, there's no happy medium; it either won't read at all, or at a slightly higher value it will read this spurious value at high power.
Is there a simple band-pass filter I can insert into the circuit to clean up this input and get a nice power reading? Has anyone solved this issue?

Thanks.

I have struck a couple of installs with this problem- some you can fix by tweaking the sensitivity, but I have found the quickest, simplest, most reiable solution is to fit a UMA rotation sensor to the mag body. Aircraft Spruce sell them (10-02432, 10-02433). Rock solid across the rev range.

Neat, but I don't think that can help me. That unit is 4.5" long, and I don't have that much available between the firewall and the magneto.

Don't believe that 4.5" long dimension.
The sensor fits in an inspection hole in the side of the magneto body, and will stick out about 1" max including the wiring bend.