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egt sensor


silver343124
06-23-2007, 05:00 PM
why are most egt sensors Thermocouples (http://en.wikipedia.org/wiki/Thermocouples) not Thermistors (http://en.wikipedia.org/wiki/Thermistors) type?
Is there anything to do with sensor response tyme?

most temp sensors like coolant temp sensor or IAT sensor are thermistor type!

KiwiBacon
06-23-2007, 10:12 PM
They're all K type thermocouples.

I have two, one has a 3mm stainless housing, the other has a 6mm stainless housing.
As you'd expect the response times are hugely different. The smaller one would take 2 seconds to follow a step change in throttle, the larger one probably 6 seconds.

BeteNoir
06-26-2007, 10:07 PM
Type K thermocouples are typically used for exhaust gas measurement since they will survive the higher exhaust gas temperatures where other types of sensors will fail. The output from a thermocouple is a voltage while the output from a resistance type sensor is a change in resistance.

The more interesting question is why someone would want to measure EGT in the first place?

KiwiBacon
06-27-2007, 12:45 AM
The more interesting question is why someone would want to measure EGT in the first place?

Is that a serious question?
EGT is one of the most informative and responsive gauges of engine load, especially in diesels.

silver343124
07-02-2007, 06:04 PM
Type K thermocouples are typically used for exhaust gas measurement since they will survive the higher exhaust gas temperatures where other types of sensors will fail. The output from a thermocouple is a voltage while the output from a resistance type sensor is a change in resistance.

The more interesting question is why someone would want to measure EGT in the first place?

I know how each of them works.

they aren't all thermocouples, IAT, and engine colant are allways thermistor type. And you have a lot of thermistors that can take temperatures up to 1100 deg C for a longer time.

here you have toyota's sensor explanation.

BTW they are all thermistor type
http://www.autoshop101.com/forms/h32.pdf

KiwiBacon
07-02-2007, 07:10 PM
they aren't all thermocouples, IAT, and engine colant are allways thermistor type. And you have a lot of thermistors that can take temperatures up to 1100 deg C for a longer time.

The post was asking about EGT, that's "Exhaust Gas Temperature". They are all thermocouples.

silver343124
07-03-2007, 07:34 AM
The post was asking about EGT, that's "Exhaust Gas Temperature". They are all thermocouples.

the post was asking WHY....

and I did not get suficient answer since on the market there are a lot of thermistors that can take much higher temperature than 700-900 deg C of exhaust gases.
Thermistors can also have very fast responce, due to its small mass - for instance IAT is fast responce thermistor.

and the responce about toyota tech site would be desired!

KiwiBacon
07-03-2007, 08:11 PM
the post was asking WHY....

and I did not get suficient answer since on the market there are a lot of thermistors that can take much higher temperature than 700-900 deg C of exhaust gases.
Thermistors can also have very fast responce, due to its small mass - for instance IAT is fast responce thermistor.

and the responce about toyota tech site would be desired!

The toyota article doesn't mention EGT probes. It mentions EGR which is a lot cooler.

The response time of an EGT probe is more related to the protective sheath it is in than the sensor itself. See my original post about my 3 & 6mm thermocouples and their response times.
The environment surrounding an IAT sensor and and EGT probes are very very different.

silver343124
07-05-2007, 08:17 AM
one technical question...

since thermocouple measure relative temperature, we actualy need two thermocouple sensors and one thermistor, as the picture below shown.
thermistor is not on the picture but, it should be where const temp on the picture is. Then the signal must be amplified and modified as the table show.
so are termocouple probes only thermocouple sensors or they have all it takes - 2 thermocouple sensors, thermistor sensor, signal amplifier and signal linearization electronics, so we get voltage that represent absolute linear temperature?

http://www.thesensorconnection.com/images/SchematicThermocouple.jpg

KiwiBacon
07-05-2007, 03:51 PM
one technical question...

since thermocouple measure relative temperature, we actualy need two thermocouple sensors and one thermistor, as the picture below shown.
thermistor is not on the picture but, it should be where const temp on the picture is. Then the signal must be amplified and modified as the table show.
so are termocouple probes only thermocouple sensors or they have all it takes - 2 thermocouple sensors, thermistor sensor, signal amplifier and signal linearizationelectronics, so we get voltage that represent absolute linear temperature?



Thermocouple probes are simply a junction of two dissimilar metals enclosed in a stainless sheath. The output is a small voltage that depends on the temp difference.
The signal amplification and conditioning is all done in the reader (whether it be a hand held multimeter or an in-dash gauge).

The cold/hot junction compensation is not an issue for EGT gauges because the temp being measured is soo much higher than ambient that the potential error is insignificant. But if you're trying to accurately read a temp which is only a few degrees higher than ambient air they are not the best choice unless you have hot/cold junction compensation as shown in the diagram you just posted.

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