Weird tach indication problem

[Delta Whisky]

The resistor is inserted in the tach line. I'm guessing the impedance of the RPM measuring circuit is pretty high so a high value, in-line resistor is needed to ensure spurious signal voltages are dropped below the measurement threshold.

[Maverick]

I ordered what the GRT document listed (10k ohm resistor 1/4 watt) for the 912/914. When I install the B&C, I'll install this. I assume it goes between the engine tach lead and the GRT. Is this correct?

Since these look like they belong on a circuit board, is there a particular method for splicing them into the wire?

[Eric Page]

Since these look like they belong on a circuit board, is there a particular method for splicing them into the wire?

I would cut the resistor leads to about 1/2" in length, then bend them back on themselves 180 degrees to make a 1/4" hook. Do the same with the wires you want to connect. Slip three lengths of heat shrink tubing over the wires: two small pieces to cover the joints and one longer piece to cover the entire assembly plus 1/2" on each end. Hook the wires and resistor leads over each other and press them tightly together. Hold the assembly straight and solder the joints. Shrink the short pieces of heat shrink over the soldered joints, then the longer piece over the assembly. Support the assembly at each end and in the middle so the resistor leads can't bend due to harness weight or vibration.

[Delta Whisky]

Maverick - yes, put the resistor in the one lead going to the EIS. Follow Eric's instruction and all will be well. The GRT EIS uses only one of the tach leads off of a 912 so Spook's schematic won't be the one to use in this instance.

[Spook712]

So in line in the + line?


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[Delta Whisky]

It sounds like your system uses both of the tach leads. (I'm assuming we are talking about a Rotax.?) If that is the case, I'd try it there. Good luck.

[Spook712]

Yes, the instrument has a RPM+ and RPM- input


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[Spook712]

Problem solved, a 220Ohm 2 Watts Resitor did the trick


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[Delta Whisky]

This is good news. Thanks for the update - one more tool in the tool box.

[Maverick]

My only concern is soldering. I can never seem to get the solder to grab onto the wires. I hate doing it. I don't know how electronics guys do it. Any tips for this? I've got my resistors and will do this once it gets too warm to fly which won't be long. . . unfortunately.