High base resistance allows for the use of long lead extensions. Lead wire can be common copper. Limitations are its limited temperature span, fragile nature, initial drift, non-linearity, lack of interchange ability. Does not provide a fail safe condition if the element should open. RTD Wire wound device, typically from Platinum wire, displaying linear resistance change with temperature.
Temperature coefficient is positive.
Precision devices for applications requiring accuracy, long term stability, linearity and repeatability. Also low base resistance prevents the use of long leads lengths, which have a measurable resistance and cause temperature indication errors. Three wire sensors, where a third wire senses the lead resistance, overcome the lead length problem. Thermocouple A junction formed by joining two dissimilar metals, which is electrically isolated from the sheath. Results in a measurable and repeatable voltage at the junction which is a function of temperature.