Difference PT100 and K probe

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gr3

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I know K has 2 wires and PT100 has 3. But is one better than other?
 
Rumor has it the PT100 is more accurate and remains consistent over time better than a k-type thermocouple.
 
RTDs tend to be a bit more accurate but as technology has advanced the differences are becoming small. Thermocouples are more physically robust.

Note that the two require very different circuitry (thermocouples are active, RTD's passive) so make sure you get something your controller can connect to. Many will do either (by choosing the correct terminals, moving a jumper etc.) but some are set up for one or the other.
 
To expand:

Thermocouple- it's a probe that uses two different metals joined at a point (the actual thermocouple), that junction generates a small voltage in relation to the temperature, that's why AJ said they are active. There are many types out there with different metals making the probe. Most common are type K and type J. To use them all wire from the temperature reading device to the probe has to be made of those same metals or you will have errors. So you have a K probe connected to K extension wire.


RTD (resistance temperature device)- is a resistor/ resistance that is known at a certain temp that make up the probe. Temperature effects the actual resistance. Typical types are PT100 and PT1000. There are two wire, three wire and 4 wire most commonly used. One wire goes to one side of the sensor and the others all go to the other side. These extra wires help cancel out the resistance of the wire itself. Almost any wire can be used to extend the probe length.

Both styles work just fine. I have a mixture of both. TC's are faster in response time than RTD's but that not a concern for us Brewers.
 
One wire goes to one side of the sensor and the others all go to the other side.
In the 3 wire configuration 1 wire goes to one side of the resistor and the other two go to the other side. This allows the use of a bridge circuit to cancel the actual wire resistances. In the four wire configuration two wires go to each side of the resistor. Two are used to supply the excitation current and the other two to sense the voltage across the resistor. Since voltage measuring circuits can be very, very high impedance the resistance of the wires connected to the voltmeter is immaterial. Since excitation is by a precision current source the resistance of the excitation wires doesn't matter either.
 
In the 3 wire configuration 1 wire goes to one side of the resistor and the other two go to the other side. This allows the use of a bridge circuit to cancel the actual wire resistances. In the four wire configuration two wires go to each side of the resistor. Two are used to supply the excitation current and the other two to sense the voltage across the resistor. Since voltage measuring circuits can be very, very high impedance the resistance of the wires connected to the voltmeter is immaterial. Since excitation is by a precision current source the resistance of the excitation wires doesn't matter either.


Thanks AJ, never used a 4 wire, only TC's in the nuclear industry.
 
They seem to be pretty rare in industry. Perhaps they are used more in the very accurate calibration instruments. Guess the bridge circuit sans current source is cheaper.
 
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