Tach from EI and Mag?
 

I have a Lightspped EI and a single mag setup, and am using a GRT EIS4000 for engine monitoring. Is it possible to get RPM from BOTH sources so that in the event one fails, or is switched off for any reason (runup) you can still see RPMs?

Thanks,
Bart

I have the same setup

I just tolerate the 10 seconds that I don't have a rpm reading at run-up.

You're not going to take off with an electrical failure with half of the ignition system if the EI is out.

And

If it quit in flight and you had to find home on the ground with the mag only, I doubt knowing the exact rpm would be much of an issue.

Yes.
 

There is an update to the EIS that you can purchase that among other things handles two ignition systems.

I did it and it worked as advertised using a mag and a P-mag (EI).

Call Sandy at GRT and she will make it happen.

James

Tach Pick up
 

Here another type of isolated tach pick-up that works well to signal your EFIS that is not affected by Mag or EI swithing or pulse count differences.
Aircraft Spruce link. http://www.aircraftspruce.com/catalo...endingUnit.php

Thomas S.
www.g3ignition.com

You can also wire a switch to change tach inputs. I usually leave it set to the mag input, because the RPM drop when turning off the mag is minimal. The Lightspeed produces twice as many pulses, which requires dividing by 2 to get the correct RPM number in my setup (I would only have to do this if the mag failed).

Electronics International Inc. offers a tach "R-1-4LM"

Utilizes both the EI square wave and a mag. It will show you mag drop, as well as an "outage" of either ignition source. FWIW.

Best to you,

Matt

Latest EIS can do both
 

I got a note from Sandy indicating the latest version of the EIS can accommodate dual Tach inputs from different type sources. So you would not have to divide by two when switching from reading the LS vs Mag.

Bart

James,
Can you post what your EIS settings you are using to make this work with the new modification? ie High/Low Pulses per Rev 1/2.... etc.

I have the same issue with my EIS. I talked with Sandy the week before Oshkosh. She told me about this upgrade. It cost $100. You ship your unit back to them, they make the upgrade and ship your unit back. She said there is a quick turn around. However, because of Oshkosh they will not be back into the shop until August 9th.

Allen mentions putting a switch to change the tach input. This would not work on the EIS 4000 unless you changed the pulse input setting for the tach each time you switched from EI to mag as they require different pulse inputs.

Actually it works fine, but with the pulse input set for a mag the EI setting on the switch causes the RPM to read too high by a factor of 2. Its not difficult to do the division. The switch really is just there to provide backup if the mag fails to provide a good signal. I generally don't use it to check RPM drop, because the drop with the mag switched off is much smaller than with EI switched off.

The upgrade to two-channel tach is definitely a better option if you're starting from scratch and don't mind spending a bit more (this wasn't available when I did mine).