Whilst it is perfectly possible to connect a Pt100 with a two-wire connection it is important to recognise that this will introduce measurement errors due to the resistance of the lead wire. This is because the measuring instrument will measure the total resistance of the measuring circuit and not just that of the sensing element itself.
If you consider that the resistance changes per degree Celsius of temperature change is just 0.3851Ω, then it can be seen that by adding in connection wires with a resistance of even just 1Ω would lead to an error approximately +2.6°C. This falls outside of the published tolerances for this type of sensor.
Two wire connection is often used and Process Parameters many sensors with this type of connection. It is often used as a lower-cost solution They are however suited to a few special cases as follows: –
- Where the application does not have a high demand for accuracy.
- Where the sensor cable is very short.
- Where the error is determined by testing and an offset applied to the measuring instrument.
If your application demands do not fall into these then there are standard methods of compensating for the lead resistance.