Thermocouple and translator box for AIT signal

AHarada · 09-26-2008, 12:22 AM

Since our cars have horrible AIT sensor heat soak issues, on top of having extremely slowly reacting sensors, it seems like there would be a good benefit to have a more accurate, faster reacting system. Many relocate their sensors to an area less prone to heat soaking (away from the UIM). This may help, but doesn't address the real problem IMO.

I did some experimenting tonight and it proved to me that the stock sensor is very sluggish when it comes to registering temp changes. I blew a hair dryer into the primary port of the UIM and kept an eye on the temp and voltage readings from my commander. The temps did go up fast. After blowing compressed air into the port to clear out all the hot air I just blew in there, the sensor dropped only a few degrees. Then took about a minute to return to reading ambient temp. It dropped steadily throughout the minute, but there was no actual change of the temp in the UIM.

So my plan is to use a fast reacting thermocouple, placed in the elbow, wired to a simple circuit translator board. Then the translator sends a 0-5V signal to the ECU.
http://www.simplecircuitboards.com/Thermocouples.html

Output calibration wouldn't be hard at all to figure out. We could just heat the stock sensor up to various temperatures, and log the temperatures as well as the voltages (sensor check screen) via the commander.

The ECU interprets a 0-5V signal. The sensor is a PTC (positive temperature coefficient) type, meaning as temp goes up, so does resistance. So I'm guessing the ECU sends a 5V reference signal, and uses the returned signal as it's temp signal. The stock AIT sensor has a green wire and a brown/black stripe wire. I'm not sure which one is which, but that's not hard to figure out.

So the output from the translator box spliced to whichever wire is the temp signal, and done.

Thoughts?

cewrx7r1 · 09-27-2008, 07:05 PM

According to the spec sheet for those:
Output = 10 mV per C.
Thus at 30C the output would be 300 mV.

The strock one runs off 5VDC and the resistant changes varies the voltage.
You would need another converter!

09-26-2008, 12:22 AM	#1
AHarada Rotary Fanatic Join Date: Mar 2008 iTrader: (1) Posts: 162 Rep Power: 17	Thermocouple and translator box for AIT signal Since our cars have horrible AIT sensor heat soak issues, on top of having extremely slowly reacting sensors, it seems like there would be a good benefit to have a more accurate, faster reacting system. Many relocate their sensors to an area less prone to heat soaking (away from the UIM). This may help, but doesn't address the real problem IMO. I did some experimenting tonight and it proved to me that the stock sensor is very sluggish when it comes to registering temp changes. I blew a hair dryer into the primary port of the UIM and kept an eye on the temp and voltage readings from my commander. The temps did go up fast. After blowing compressed air into the port to clear out all the hot air I just blew in there, the sensor dropped only a few degrees. Then took about a minute to return to reading ambient temp. It dropped steadily throughout the minute, but there was no actual change of the temp in the UIM. So my plan is to use a fast reacting thermocouple, placed in the elbow, wired to a simple circuit translator board. Then the translator sends a 0-5V signal to the ECU. http://www.simplecircuitboards.com/Thermocouples.html Output calibration wouldn't be hard at all to figure out. We could just heat the stock sensor up to various temperatures, and log the temperatures as well as the voltages (sensor check screen) via the commander. The ECU interprets a 0-5V signal. The sensor is a PTC (positive temperature coefficient) type, meaning as temp goes up, so does resistance. So I'm guessing the ECU sends a 5V reference signal, and uses the returned signal as it's temp signal. The stock AIT sensor has a green wire and a brown/black stripe wire. I'm not sure which one is which, but that's not hard to figure out. So the output from the translator box spliced to whichever wire is the temp signal, and done. Thoughts?

09-27-2008, 07:05 PM	#2
cewrx7r1 The Judge Join Date: Feb 2008 iTrader: (0) Posts: 196 Rep Power: 17	According to the spec sheet for those: Output = 10 mV per C. Thus at 30C the output would be 300 mV. The strock one runs off 5VDC and the resistant changes varies the voltage. You would need another converter!