My take on this is that the circuit and firmware in the EC2 is set up for a
specific sensor.  The early version used a 10K thermister, and the later
version, a 3K.  In putting in some other sensor than the one Tracy supplies,
you best have some input from Tracy.  If yours has about a 3K resistance at
ambient, it may be OK.

In the current version one side is connected to pin 1 (ground) and the other
to pin 31.  Early version connected pin 11 (+5v, I think) and pin 31.

I'm having some issues with mine right now, and it may be because I have a
10K sensor, and a newer replacement ECU.  You can connect a fixed resistor
in place of the sensor (probably a 3K Ohm in your case), and it will work
just fine until you are sure what you need. Al


To: Rotary motors in aircraft
Subject: [FlyRotary] EC2 probe grounding.

Just pinging the group on this.

Chris (and every once in a while I) are to the stage of wiring up goodies to the EC2. We have the injectors, resistors and most of that stuff done. Next is the inlet air temp sensor for the EC2 (to be followed by all the other sensors for the EM2).

There are two wires for the EC2 air temp sensor. There are conflicting instructions and diagrams with regards to a new and old scheme that involve 2 of 3 possible pins on the plug (I think it was 1, 11 and 31, but not positive - you can look at the EC2 diagrams regarding this.

Anyways, the VDO air temp probe I am using is a 1/8" NPT 300 degree F with a terminal on top that can receive a female spade connector.

The top terminal is clearly insulated from the rest of the probe, and the body of the probe is the ground.

What is the best method for wiring this type of probe.. obviously one wire to the top terminal, the positive if so designated. But do we put a ring terminal on the body of the probe and hook up the second EC2 wire to it? Or do we consider the engine block the ground, which the intake will be firmly attached to, and connect the second wire to our forest of tabs grounding block on the firewall.

It seems that grounding the probe with a ring terminal can introduce a ground loop because now there are two potential paths back to the EC2. Are the air temp leads electrically isolated (transformer coupled, for instance) or is a ground loop possible.

More than anything else, I would like to hear from those of you who are flying with the EC2, because at this point I need practical, not theoretical help. I know Tracy is off the grid, so I may wait a while to hear from him, but the rest of you with EC2 rotary time, please tell me how your set-up is set up.

Dave (and Chris)

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