Risk of self-heating
The current through the sensor will cause some heating: for example, a sense current of 1 mA through a 100 ohm resistor will generate 100 µW of heat. If the sensor element is unable to dissipate this heat, it will report an artificially high temperature. This effect can be reduced by either using a large sensor element, or by making sure that it is in good thermal contact with its environment.
Using a 1 mA sense current will give a signal of only 100 mV. Because the change in resistance for a degree celsius is very small, even a small error in the measurement of the voltage across the sensor will produce a large error in the temperature measurement. For example, a 100 µV voltage measurement error will give a 0.4 °C error in the temperature reading. Similarly, a 1 µA error in the sense current will give 0.4 °C temperature error.
Because of the low signal levels, it is important to keep any cables away from electric cables, motors, switchgear and other devices that may emit electrical noise. Using screened cable, with the screen grounded at one end, may help to reduce interference. When using long cables, it is necessary to check that the measuring equipment is capable of handling the resistance of the cables. Most equipment can cope with up to 100 ohms per core.