What is the standard and tolerances for RTD Pt100 Sensors?

Pt100 sensor accuracies are defined under IEC 60751 and are commonly referred to as IEC standard or DIN standard. This standard requires that the Platinum resistance (sensing) element has a resistance at 0ºC of 100.00 ohms (hence the acronym Pt100) and a temperature co-efficient (change in resistance per ºC) of 0.00385 between 0 and 100°C.

The two most widely used tolerances specified in IEC60751 are as below:
at 0ºC: Class B = ±0.12 ohms / ±0.3ºC
at 100ºC: Class B = ±0.30 ohms / ±0.8ºC
For other temperatures, use the equation: ± (0.3+0.005 |t|)

at 0ºC: Class A = ±0.06 ohms / ±0.15ºC
at 100ºC: Class A = ±0.13 ohms / ±0.35ºC
For other temperatures, use the equation: ± (0.15+0.002 |t|). Tolerances for the range -200ºC to +850ºC are also shown in the table below.

There are also some tighter tolerances available which are generally accepted in industry but may be given different numbers from different suppliers:
1/3 DIN (1/3B) = ±0.040 ohms / ±0.10ºC (at 0ºC) or ±1/3 (0.3+0.005 |t|)
1/5 DIN (1/5B) = ±0.024 ohms / ±0.06ºC (at 0ºC) or ±1/5 (0.3+0.005 |t|)
1/10 DIN (1/10B) = ±0.012 ohms / ±0.03ºC (at 0ºC) or ±1/10 (0.3+0.005 |t|)

It is worth noting that whilst 1/3 DIN is a widely used term, it and the other fractions are not included in the standard. However, the IEC 60751:2008 standard includes the tolerance class 'AA' which is almost identical to 1/3B; having the equation ±(0.1+0.0017 |t|).

Pt100 Tolerances according to IEC 60751

Temperature Class A Class B
±ºC ± Ohms ±ºC ± Ohms
-200ºC 0.55 0.24 1.3 0.56
-100ºC 0.35 0.14 0.8 0.32
0ºC 0.15 0.06 0.3 0.12
100ºC 0.35 0.13 0.8 0.30
200ºC 0.55 0.20 1.3 0.48
300ºC 0.75 0.27 1.8 0.64
400ºC 0.95 0.33 2.3 0.79
500ºC 1.15 0.38 2.8 0.93
600ºC 1.35 0.43 3.3 1.06
650ºC 1.45 0.46 3.6 1.13
700ºC - - 3.8 1.17
800ºC - - 4.3 1.28
850ºC - - 4.6 1.34

Specifying a Pt100 sensor

Once the required tolerance / accuracy class for the application is established and the number of wires required for the instrumentation is known, the next consideration when specifying a Pt100 sensor is on the more practical side so as to specify a sensor able to withstand the temperature range and physical needs of the application.

We offer a wide range of Pt100 sensor styles and constructions and there are sensors in this range to suit a wide range of applications from immersion sensors to surface and air temperature measurements.

If we look at a basic immersion or general purpose RTD Pt100, then we must first look at the temperature range required. Most Pt100 applications tend to be lower temperature measurements when compared to those required of thermocouples and our general purpose sensors are a good choice for applications up to 250ºC. If a higher temperature than this is required, then our mineral insulated Pt100s are a good choice. These are rated for use up to 600ºC and also have the advantage that they can generally be bent or twisted to suit the application space. Both styles of sensor are fitted with a length of cable for easy connection to instrumentation.

Beyond this, some applications may require a terminal head to be fitted to the sensor which may also include a 4 to 20mA transmitter. Other requirements may require a connector to be fitted to the RTD sensor, so that extension leads can be attached or so it can be connected directly to an instrument.

There are also some more specilised applications such as surface temperature measurements where we can supply magnetic Pt100's, self adhesive patch RTDs and Pt100's for pipe surface measurements.

Where applications require a fast response to temperature changes or where the application requires a smaller sensor, we offer a range of miniature Pt100 sensors and a range of Pt100s with a swaged tip.

For applications requiring the measurement of air temperatures, we can supply sensors with perforated tips which allow airflow around the sensing element. Indoor air temperature RTDs are also available for energy management in buildings.

There are specific sensors that have been predesigned for more specific applications such as for use in autoclaves, the plastics industry and in bearing applications and these can found on our main Pt100 sensor page.