This is old news for most of you, but the topic had come up elsewhere, so I thought I'd post:
Conventional EGT gauges use a thermocouple probe. Thermocouples work because 2 different metals will generate voltage based on the metals, and the temperature. So DO NOT extend EGT probe wires if you want accurate readings. If you must, some mfrs sell probes with longer wires, or they sell a specific adapter wire to extend it. Changing the metal composition will change the voltage output. BTW- the voltage is in microvolts, so inside your gauge is an amplifier. Some use an external amplifier. This is why your datalogger won't read EGT data through a normal 0-5v port.
Now, there is a newer kind of EGT temperature sensor. It generates resistance based on temperature, so this does not apply, and it can be read through a normal ohm sensor port. It will read from below zero, to over 1850°F more accurately than thermocouples. They are found on newer engines that use EGT sensors as part of their emission system. 2008+ GM diesels use this kind of sensor. While water temp and oil sensors work this way, they do not have the range of the new EGT sensor technology.
They might be new to the GM crowd, but RTD (resistance temperature detectors) have been around for a century.
They are constructed either from a thin-film platinum, wire wound resistor, or coiled elements. None will withstand being directly in the exhaust and have to be shielded. They are slower to respond. Slower as in seconds versus fractions of a second for a thermocouple.
RTD sensors are more accurate. Thermocouples are accurate to about 5 degrees at 1300F.
I don't think that anybody using an EGT needs better accuracy if they already have one installed. If you are looking for a new EGT it's worth a look.
Quote from: Dean Los Angeles on January 18, 2013, 09:22:23 AM
They might be new to the GM crowd, but RTD (resistance temperature detectors) have been around for a century.
They are constructed either from a thin-film platinum, wire wound resistor, or coiled elements. None will withstand being directly in the exhaust and have to be shielded. They are slower to respond. Slower as in seconds versus fractions of a second for a thermocouple.
RTD sensors are more accurate. Thermocouples are accurate to about 5 degrees at 1300F.
I don't think that anybody using an EGT needs better accuracy if they already have one installed. If you are looking for a new EGT it's worth a look.
I'm pretty sure this is a new technology. I'm having a hard time finding out how they work. The core appears to be ceramic, and has a perforated stainless tube around it, you can see the element, no wires or metal film. It reacts almost instantly, and has a huge range. Pretty bizarre whatever it is. Note the holes in the tip, and deep probe length.
Here's the test chart on it:
°C
°F
OHMS
1000
1832
849
900
1652
795
800
1472
738
700
1292
680
600
1112
618
500
932
554
450
842
521
400
752
488
350
662
455
300
572
420
250
482
385
200
392
349
150
302
313
100
212
276
50
122
238
25
77
220
0
32
200
-20
-4
185
-40
-40
170
Note, -40 is the lowest I can get. Need some liquid nitrogen. Seems it's going bottom out at absolute zero?