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Please, I want to know why there is 4 wire RTD and another type 3 wire RTD, both types pt100. What does PT100 mean?

The principle of operation is to measure the resistance of a platinum element (Platinum resistance thermometer). The most common type (PT100) has a resistance of 100 ohms at 0 °C and 138.4 ohms at 100 °C.

For a PT100 sensor, a 1 °C temperature change will cause a 0.384 ohm change in resistance. A 4 wire is the most accurate way of measurement, although 3 wire tends to be the norm.

please can you send me the electrical drawing for the pt100 that connect with the panel

try http://www.rosemount.com they have great explanation and technical drawing to help you solve that

3 wire are most commonaly uesed in Process Control, 4 wire for lab applicatiions. You can have head mounted transmitters, multiplexers etc. I suggest you look up temperature transmitters some of the Major manufactures web sites they will have wiring drawings.

Carmel

Hi,

I have another question regarding this topic. If I have a 3 wire transmitter and a 4 wire sensor, then I just "shorted" one pair of the sensor wire to become 3 wire and connect to the transmitter. Will this affect any accuracy? Please explain to me if possible.

Thank you very very much.

Rgds,
Dav

Unless the application needs the accuracy that a 4 wire device can give you, I would just not use the 4th wire. But before you do this, you might want to check you have a 4 wire device in the first place.

Steve
www.mtl-inst.com

In answer to Dav:

You can not do it that easy. I can send you a page with diagrams to show you the details.
ubtrefkou_5432@yahoo.com

Wont work I dont think.

The way I understand it is that the "third" wire is a temperature reference to compensate for ambient temperature and wire distance effects on the wire itself.

Within the RTD the reference wire is shorted with one of the measurement wires and the resistance measurement from the reference wire to the measurement wire is negated from the resistance across the two measurement wires. The results in a net resistance measurement of the RTD itself.

So.... if you shorted the two reference wires together you would get a radically reduced resistance which would skew your temperature reading.

I hope that made some sense.

Accuracy of 2 wire > 3 wire > 4 wire RTD. 3 wire or 4 wire rtds used to nullify the lead wire resistance in addition to actual RTD resistance for long distance cable runs.

The RTD only has two ends, two wires are connected to each end. Since these wires are quite short it will have little effect if you short two together, it's normal though just to ignore the 4th wire. You would only wire as 4 wire if you needed accuracy better than 1 decimal place.

Regards
Roy