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AF2500 Pressure Senders with GRT EIS?

Canadian_JOY

Well Known Member
Making a change of equipment... Out with the old, in with the new.
The old... AF2500 engine monitor.
The new... GRT EIS-66R.

I've purchased the GRT oil pressure sensor and fuel pressure sensor (engine has a carb so this is the low pressure sensor) manufactured by VDO. I have to admit I'm totally unimpressed by the method of connecting the VDO fuel pressure transducer to the EIS - a kluge of resistors to get the right range to work with the AUX input. Not exactly my idea of an "aircraft grade" installation.

Has anybody successfully used the AF2500 pressure sensors with the GRT EIS? The AF2500 sensors in question are the small-diameter senders with 3-pin connectors on the end, supplying power and ground from the ACS2002 analog module and piping a 0-10V signal back to the analog module. These are very slick (not to mention expensive) senders - far better quality than the VDO units that GRT supplies.

Thanks for your helpful replies.
 
The oil sender is fixed, but all others are done in software vi offsets. I installed transducer style sensors on my EIS system
 
Thanks for your comments, Larry.

From your comment I understand engine oil pressure is looking for straight resistance to ground, thus the preference for the VDO. I'm wondering if one could just use the signal wire from the AF2500 sensor (I haven't checked to see if the AF2500 oil pressure sensor is just a resistive sensor or if it does anything more fancy with the signal output)?

Which sensors did you use, and how did you wire them? I'm assuming you used the EIS 4.8V sensor excitation provided by the EIS? In the AF2500 the pressure transducers were powered by +5V thus I think the AF2500 was looking for its signal input as a voltage ratio referenced to ground.
 
As Larry stated, the oil pressure is dedicated to use a VDO resistive sensor.

All the aux inputs can be customized to your application. In the EIS manual there is discussion of Transfer functions. Essentially the EIS assumes that the data stream is in the form of a straight line, y=mx+b. You define y which is the scale factor and b which is offset. You modify them by a factor of 10 to get integer or decimal displays. I have a more detailed discussion I can email you.

In my case the only GRT sensor I use is manifold pressure.

Jim Butcher
 
Thanks for your comments, Larry.

From your comment I understand engine oil pressure is looking for straight resistance to ground, thus the preference for the VDO. I'm wondering if one could just use the signal wire from the AF2500 sensor (I haven't checked to see if the AF2500 oil pressure sensor is just a resistive sensor or if it does anything more fancy with the signal output)?

Which sensors did you use, and how did you wire them? I'm assuming you used the EIS 4.8V sensor excitation provided by the EIS? In the AF2500 the pressure transducers were powered by +5V thus I think the AF2500 was looking for its signal input as a voltage ratio referenced to ground.

I used kavlico knock offs for fp and it is powered from the eis 4.8 vec output and the .5 to 4.5 voltage return goes to the aux input. Youneed a bit of math to get the settings right, but no resistors

Op is a non adjustable input, so must use the vdo sensor to get it to read correctly. I dont see how you could use a kavlico for this, as the eis will have an internal pull up and be looking for a resistance to grd. As well as a fixed table for voltage to presssure

The eis box is clever for 80’s technology, but woofully behind by modern standards. It is really forced into the market today by grt refusing to duplicate the functionality in their efis units
 
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Circling back on this one following completion of installation of the GRT EIS-66R in place of the previous AF2500 engine monitor.

Firstly there are two important bits of info one needs to consider. The EIS-66R (remote) EIS is DIFFERENT from an EIS4000. It runs different software. It has different sensor calibration interactions.

Secondly, the EIS-66R contains an internal MAP sensor. This makes installation a bit easier (once you discover the undocumented size of the required tubing to hook it up!). The down-side is that, unlike the EIS4000 with its remote-mounted MAP sensor, with the EIS-66R its internal MAP sensor cannot be calibrated via the usual slope and offset adjustments one would come to expect. What you get is what you get, period.

I ended up installing all of the GRT sensors rather than trying to re-use any of the AFS sensors, even though the AFS sensors are clearly higher-quality units. One should note that even the AFS carb temp sensor cannot be reused as the GRT sensor uses a different resistance range and the opposite temperature vs resistance coefficient.

The exception to the statement above is that I re-used the AFS EGT and CHT sensors as they are thermocouples so are pretty simple devices and the AFS EGT probes seem to be longer-lasting than the stock GRT probes.

That's about it for now. Still working out some minor details with the installation but generally am pretty happy with the overall result, and very happy that now I have an EFIS over on the right side of the panel and it can display engine data where with the AF2500 that panel real estate was dedicated to engine monitoring.
 
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