MGL Sluggish Tach Indications (Dual P-Mags)

Bob Ellis · #1 05-29-2012, 03:09 PM

I have dual P-Mags sending a 2 pulse/RPM signal to an MGL single engine monitor (E3) and to an MGL Voyager. All use the same single point ground from the engine block

The E3 is not displaying any RPM and the MGL Voyager display is sluggish. The test pilot noted that an RV-7 that he flew last september that had an MGL Odyssey using a traditional mag pick up was also sluggish wheras the analogue tach was spot on.

Does anyone have any experience with either Dual P-Mags and MGL EFIS equipment or sluggish RPM with Dual P-Mags and a.n.other EFIS?

Anyone using Vans TACHGEN transducer with MGL equipment successfully?

Regards

Bob Ellis
www.rv-8.co.uk
First flight 23 May 2012

chepburn · #2 05-29-2012, 03:16 PM

Bob,
I noticed this as well on my Odyssey installation. I queried Matt at MGL USA, and I was told that the input software filter is biased towards higher RPM...so, when you are doing a mag check at lower RPM, the response is slow to integrate. Yes, it is annoying.
At cruise RPM, the lag is not as noticable.

Chris

jbagley · #3 05-29-2012, 03:42 PM

I'm using the UMA tach sender that MGL sells and have the same experience. Slow response at low rpm. Annoying.

Omega232Devils · #4 05-29-2012, 03:52 PM

I have dual PMags with Vision Microsystems VM-1000 engine monitor and no lag at all. PMags are set to 1 ppr and diode to send 5V signal that my VM1000 requires.

chepburn · #5 05-29-2012, 03:53 PM

Quote:

Originally Posted by jbagley

I'm using the UMA tach sender that MGL sells and have the same experience. Slow response at low rpm. Annoying.

James,
Someone with more knowledge may correct me, but I don't think it has anything to do with the UMA sensor. I believe it is a software issue..

jbagley · #6 05-29-2012, 04:03 PM

I think it's partially software... As in, depending on how many pulses per revolution the transducer produces it may affect the response time of the software? In any case, it's another data point.

I used the P-Mags directly the same as Bob (original poster) before installing the UMA transducer at MGL's recommendation. The rpm doesn't jump around as much, but still sluggish at low rpm. I've decided that it's annoying, but short of replacing the MGL instrument not much I can do about it.

Quote:

Originally Posted by chepburn

James,
Someone with more knowledge may correct me, but I don't think it has anything to do with the UMA sensor. I believe it is a software issue..

Bob Ellis · #7 05-29-2012, 11:47 PM

Thanks for the responses so far guys.

As Dan has no issues with his VM1000 at 1 pulse/rev (assume he altered that as the manual says two is standard) it would appear that the P-Mag pulse is strong.

My aircraft is grounded awaiting a spare for the engine so I will have to do an engine run post maintenance. As the MGL screens are programmable I will remove all AHRS/Compass/GPS screen items and just leave the bare minimum engine items to see if the MGL processor was overloaded. If the RPM is still sluggish then there is another issue.

Regarding RPM sensitivity bias I would have thought that our pre-take off check RPM would be the most important due to the mag drop check not high RPM's.

Will feedback my results next week.

Regards

Bob
www.rv-8.co.uk

Omega232Devils · #8 05-30-2012, 12:13 AM

Hi Bob,
Just want to clarify so as to not add to any confusion.

The PMAG comes from the factory set at 2 PPR, I used EICAD to change the setting to 1 PPR. (My other option required unhooking about 40 wire connectors, removing the DPU, opening the case and changing a jumper setting to accept 2 PPR) I believe all the DPU would do if the jumper is set to accept 2 PPR is divide the signal by 2.

Wish you luck with your issue.

Dan