What are the different types?
Most users of temperature probes will be familiar with the terminology Pt100, Pt500 or Pt1000. These are the standard values for this type of sensor, but what does it mean?
Pt is the chemical symbol for Platinum and denotes its use in the sensor. Other sensors may use Cu (copper) or Ni (Nickel) accordingly.
The number relates to the resistance value at 0°C. So a Pt100 probe will have a resistance of 100Ω at °C, and it follows that a Pt1000 RTD will be 1000Ω at 0°C.
How does the PT100 sensor work?
As the temperature in your application changes then the electrical resistance will also change. An increase in temperature will increase the resistance of the temperature sensor.
The measurement is completed by your instrument by applying a small measurement voltage and utilising a bridge type circuit.
Are RTD’s interchangeable?
Yes. All sensors manufactured by Process Parameters Ltd conform to the relevant British and International standards that apply. In the case of Platinum Resistance Thermometers we apply BS EN 60751 which covers the characteristics, accuracy and colour coding systems used. This means that you can take a Pt100 and replace it with another and it will simply work, there is no need for any configuration. In some applications there is a requirement for a procedural calibration check.
PT100 Temperature Sensor or Thermocouple?
Thermocouples are made with two dissimilar metals or conductors where a temperature difference between the hot and cold junctions (join) of the thermocouple generates a small voltage signal which changes with temperature. They are best suited to elevated temperatures (up to 1700°C) or very low temperatures (down to -200°C) and are also ideal where there is any vibration (where a Pt100 is more likely break). If you need a fast response temperature sensor we recommend the use of thermocouples.
How accurate are RTD’s?
Part of the standard that we operate to governs accuracy. In theory a RTD pt100 can be extremely accurate but you need to consider a few factors when thinking about accuracy.
First of all there are five accuracy bands; Class B, Class A, 1/3 DIN, 1/5 DIN and 1/10 DIN. Class B is the least accurate, 1/10 DIN is the most accurate. The table below gives the accuracy for each tolerance band at different temperatures. Note that accuracy is best for all classes at 0°C and worsens for increasing and decreasing temperature.
