EFILive LMM Pyro for datalogging EGT's

[McRat]

This is something I started playing with back in 2007 and had it working, but then got sidetracked.

Here's the thing, the LMM pyro will read from absolute zero (-460?)F to 2000+ degrees. Unlike a convention pyro, it's a thermistor. That means it's resistance (ohms) varies based on temperature.

A conventional pyro outputs voltage, measured in millivolts (thousandths of a volt) and needs an amplifier if you want to drive a gauge with it. This is why pyros are more expensive than other gauges. And they have short lives when exposed to very high heat because they are two different metal connected at the end. The metals expand at a different rate and eventually break the connection at the hot end.

The LMM pyros are readily available, sometimes for free, and have survived inside Casper for over a year.

Using boiling water, room temperature, refrigerator, and freezer in my kitchen, I came up with this:

275ohms = 212 F
218 = 72 F
204 = 40
191 = 10

Appears to origin at absolute zero, -460 F

Each ohm is 2.45 deg F in this range when offset by 460 deg F.

Truck idles at 200F - 268o

But later I found (thanks Cobra) the GM table for the translation, and found that 2.45 deg/ohm is only good from -40 deg to 700 deg. Those temps can be OK for IAT temp use, but not for pyro use.

To get good accuracy up high, I came up with a formula: Ohms^1.19 - 1.11*Ohms - 292 = degrees F.
This good to within 10 deg F from 1832F to -40F. There is a more accurate formula, but even this is beyond the accuracy of everything else in the system.

Now to make this into a Calculated PID. Next step.

 

[McRat]

Next step would be to get the readings in a format EFILive can understand.

Remember those orange plastic thingies in your EFILive box? Those are external data ports connectors you screw wires into, then plug into the bottom of the V2 unit. But they read in 0 to 5 volts, not ohms, so first we need to turn ohms into voltage.

Well, it's no secret to anyone I hate electricity. But I did figure two things:

Your voltage in your truck will vary from 12.0 -14.5 volts, this is too much range to use for gauges without a voltage regulator. Use P/N 7812 from Radio Shack will hold the voltage still enough for use. The center pin is ground, the left pin goes to any 12v source on your truck, and the right pin gives you 12.0 volts anytime the engine is running.

Second, while more range between the reading voltages is better, the only thing I could figure out was to use a 1200 ohm resistor to bring the voltages down to 4.9v at 1832 F, and 1.84v at room temperature. I really want 4.9 volts at 1832 F, and .5v at 400 deg F so I have more accuracy to the data, but I don't how to do that yet.

 

[motohed]

you are way too knowledgeable for me to handle i hate electricity

 

[McRat]

looking

 

[kidturbo]

Did you ever get that LMM sensor scaled out?

I was working on a similar mod to use the LMM probe with the V2 a while back but lost interest. I did manage to get a donor LMM probe mounted up in a regular EGT k-type socket [see pic below] before I quit on it. Ya gotta drill out the socket [I used a carbide DG bit], then trim down the ring on the probe with a grinder, but they WILL fit nicely in a standard EGTprobe spot when done.

If someone has 3 known temp points [high, med, low] on the ohms scale, I do have a cool program to chart the rest of the scale that I used for the IAT mod.

Sorry for the poor pic. A hose and the heat shielding is blocking this view, but it's wired in and ready to test with. Somewhere I have pics of the socket mod also.