Handy, Cheap Thermocouple Amplifier Circuit....

**Pete@IE** · 08-15-2008 06:59 PM

This one goes out to all the guys with LM-1's or standalones who are into datalogging.

Hello again guys,

I've been playing around with this circuit for a little while now, and it works awesome. This will let you hook up a standard K type thermocouple and get a 0 to 5V analog output, which you may datalog, run into an ecu, whatever you feel like. It is scaled from 0 to 1100C linearly, so

0V = 0C
1V = 220 C
2V = 440 C
3V = 660 C
4V = 880 C
5v = 1100C

Here it is:

I recommend getting everything from digikey.com . I would / did build this in a project box, on a sheet of perforated breadboard. I would recommend buying a HIGH QUALITY K type thermocouple, preferably with an inconel sheath. I am using this upstream in my exhaust manifold and it is 100 times better then my VDO one which is installed right after the turbine, which is slow and unresponsive. I used a 1/4" diameter thermocouple from omega instruments.

Also keep in mind you cannot extend thermocouples with regular wire, you need to use thermocouple extension wire, or you will inadvertently basically make 2 extra thermocouples where you make the joint, which would not be compensated for by the AD595 chip. This stuff is generally only available in rolls but we may be able to provide it for you by the foot.

Also, watch out for differences in grounds between your tc amplifier circuit and your ECU. My amplifier reads perfectly when connected to a multimeter but has a voltage offset when hooked up to my haltech which i had to program out.

All in all this is a great project for a tinkerer or somebody who likes to understand the nitty gritty of how things work. It's a lot of fun and relatively inexpensive, the thermocouple and the chip are the two most expensive things, at about $20-$50 and $12ish respectively. Have fun with this guys, I know I did, and I'm going to be whipping up a few extra's to use just around the shop.

**MattzWarsteiner** · 08-19-2008 11:02 PM

EGT probe, kinda cool Pete. How do you mount the thermo thingie? Drill a hole?

**Pete@IE** · 08-24-2008 01:14 AM

Yup, same as any other kit, just drill and tap, or weld a bung on for a compression fitting, and insert your thermocouple.

**GetBoosted84** · 08-27-2008 06:17 AM

The image you posted before is not showing... can you give me a direct link or re-host?

Thank you btw. This is really helpful!

**mike-2ptzero** · 08-27-2008 08:37 AM

Might want to mention that if you have a LM1 you will also need the RPM cable which allows for 0-5 volt logging. I would try this on my LM1 but I just upgraded from the RPM cable to the LMA3 which allows for the probe to be hooked up directly to it.