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  #1  
Old 09-04-2018, 09:48 PM
Canadian_JOY Canadian_JOY is offline
 
Join Date: Aug 2007
Location: Ontario, Canada
Posts: 1,772
Default Will AFS Mag RPM Sensor Work With GRT EIS?

I'm shortly going to be removing our AF2500 engine monitor and replacing it with a GRT EIS and a Sport EX EFIS to round out the GRT equipment in the panel.

Here's my dilemma... I really like the AFS tachometer sensor that screws into the bottom of the Slick magneto housing. I like that it provides tach readings whenever the motor is spinning the magneto, irrespective of ignition switch selection. I really like that it doesn't mess with my P-leads which I consider to be two of the most critical wires in the airplane. In short, I want to keep using it.

My question to this esteemed group... Has anybody successfully made this AFS sensor work with the GRT EIS? If so, how did you do it? What settings did you use in the EIS?

I'm assuming I will have to power the sensor and provide it a ground, just as it currently gets from the AF2500. I would use the regulated sensor power output of the EIS for this function. My big concern is whether or not the EIS is capable of reading the output of this sensor.

Thanks for sharing your knowledge and experience on this topic!
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  #2  
Old 09-04-2018, 10:03 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 5,350
Default

Id call GRT and ask. But...why not use the GRT system? The GRT system ties into the P leads at the ignition switch(es) with large resistors. Even if the line shorts out downstream the mag will be unaffected. During mag check it will auto switch to the functioning mag.
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  #3  
Old 09-05-2018, 07:30 AM
Canadian_JOY Canadian_JOY is offline
 
Join Date: Aug 2007
Location: Ontario, Canada
Posts: 1,772
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Bob - thanks for your comments. I've omitted some detail in the interests of brevity. I have only one mag, which has the AFS sensor already installed, and I have the associated wiring run through a "Dan Horton" style firewall penetration. My second ignition is a P-Mag with its tach signal not run through the firewall penetration.

My interest in continuing to use the AFS sensor is two-fold... Firstly, it works and works well, while I have helped several other owners/builders troubleshoot flaky indications on other tach sensing methods, including the GRT P-lead resistor pick-off. Secondly, by continuing to use it I can avoid significant rework to the firewall penetration. And then there's the third reason... I don't like the "blink" that happens to the RPM display as the EIS switches from one tach input to the other. With this in mind I think sticking with the AFS sensor isn't a terrible plan. I just need to figure out whether or not the EIS has the capability of handling the signal. GRT tech support has been unable to provide a meaningful response however I'll be contacting AFS tech support to get a better characterization of the output signal from their sensor before contacting GRT again.
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  #4  
Old 09-14-2018, 10:05 AM
Canadian_JOY Canadian_JOY is offline
 
Join Date: Aug 2007
Location: Ontario, Canada
Posts: 1,772
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Closing the loop here for the benefit of posterity.

Firstly, a shout out to both AFS and GRT tech support. They both provided concise answers in a timely fashion.

Now let's look at the sensor itself... According to AFS the sensor is described as follows:
- the sensor can operate between 4.5V to around 16V provided between V+ and Gnd
- the output provides 20mA of latching sink current to the Gnd lead
- output is a “2 per revolution” pulse train

With this info in hand, GRT was able to provide the following guidance:
"You can connect the sensor directly to the tach input of the EIS. Set the TachP/R to 2. you may need to set the TachSens (Tach sensitivity) to "H" (default is low) if you are unable to obtain an RPM reading at low RPM."

My next comment here will likely be to summarize results of testing with the AFS magneto sensor connected to the GRT EIS66R. That might be awhile as I'm not inclined to take the airplane down for a major mod with such good weather around.
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