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Digital Tach Lag ?

7

777drvr

Well Known Member
Hi Guys,

I'm in the process of modernizing my RV-4 and have ripped out all vacuum and engine instruments and replaced them all with the new MGL Xtreme EFIS/EMS .

Everything seems to be functioning but I'm curious about my RPM indications .

There seems to be a lag in indications , most noticably on start up and shut down . I don't get any RPM indications for 2-3 s on start up and the RPM's show the idle RPM for a few seconds after shut down . Mag checks are also less responsive .

Is this life with a glass tach or is there something wrong with my setup ?

Any suggestions or comments are appreciated !

Marc
 
I'm sure there a bunch of you using EMS's from Dynon , GRT , MGL , etc...

Could I get a pirep on how responsive your RPM indications are ? Is there any perceived lag ? More at low RPM's VS higher . I've never flown behind glass in a piston plane so don't know if what I'm experiencing is normal.

Thanks,
Marc
 
What you're describing doesn't sound right.. I've never seen it on any other system (GRT, Dynon, etc..)
 
MGL Tach

I have a MGL tach in my Ercoupe. I never notice a lag during startup or when I shut the engine done, but then I don't know if I've ever checked. I have noticed a lag in my run-up, doing a mag check. When I put it on one mag , either left or right it takes a few seconds to adjust.
Russel Koch
RV9A
Working on everything.

finishing, panel and controls
 
High Frequency/Low Frequency

I have a MGL Infinity Single (small 2 1/4 engine monitor). I had the same issue with the MGL engine monitor. If memory serves me correct there is a low frequency and a high frequency setting for RPM. When I switched it to the right one (don't remember which one) the lag in RPM went away. I would bet your MGL EFIS has the same setting.
 
Dynon and P-Mag

I have the small Dynon EIS connected to a P-Mag. Works perfectly, no lags whatsoever.
 
I have an Enigma, and I do have a lag. Hadn't heard about the low/high setting...will check on that, but it's normal with the RDAC-X unit from what I know. Not a big deal, and I'm used to it now, so I don't even really notice it...I will check on the low/high tho!:cool:
 
My GRT EIS has a small lag in RPM and even a bigger lag in MP. I have been told that this is due to filtering that is built-in in the EIS as otherwise it will be too eratic. The RPM lag is very little but consistant at all RPM (high or low)

I suspect most digital engine monitor have some sort of filtering.

Hope this helps
 
Hi Guys,

I also posted on the MGL Forum and was told by Rainier that all the processing is done in the RDAC and there will be more lag with my 1 pulse per rev sender than a set up with a higher frequency .

The high/low setting is for the Infinity singles unit that does not use the RDAC interface .

I'm glad to hear from some MGL users that it's normal . Not ideal but normal !

Marc
 
I have one mag and one electronic ignition. Since my electronic ignition doesn't put out a 10v pulse, I only derive RPM from my mag for my Dynon EFIS.

When I do my runup mag check and turn of the real "mag," rpm goes to zero with about a 1/2 second lag (but no intermediate reading, or ramp-down - just says 1800 then zero). Likewise when I turn the mag back on there is about a 1/2 second delay. This makes absolute sense, since what they are doing is "averaging" counted pulses over a period of time.

Other than that, the lag is not noticeable in flight.
 
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