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English version under development, please refer to the french version for the complete information

Platinum temperature sensors (PRTD - Platinum Resistance Temperature Detector) are very commonly used in the industry for accurate measurements. Their principle is based on the variation of the electrical resistance of a platinum conductor (wire or foil) with the temperature. Their well-known electrical characteristics are stable and are described by standards as IEC 60751, ASTM E1137, ... and the previous standards IEC 751, DIN 43760, ...

The references of the common models are Pt100, Pt500, Pt1000. The name of the model indicates the value of the electrical rsistance of the sensor at a temperature of 0C. For example the most common model, the Pt100, means that the sensor has an electrical resistance of 100 ohms at 0C.

The change in electrical resistance is nearly linear with the temperature change. For example a Pt100 has a coefficient of about +0.4 ohm/C at 0C and +0.35 ohm/C at 300C.

Some sensors are able to operate in temperature ranges beyond -200C or +800C.

3-wire Pt100 sensor

3-wire Pt100 sensor

Depending on how they are manufactured, the sensors are divided into tolerance classes:

    class         at -100C       at 0C      at  100C     at 200C      at 300C

B   F(W)0.3       +/- 0.80C    +/- 0.30C    +/- 0.80C    +/- 1.30C    +/- 1.80C
A   F(W)0.15      +/- 0.35C    +/- 0.15C    +/- 0.35C    +/- 0.55C    +/- 0.75C
AA  F(W)0.1       +/- 0.27C    +/- 0.10C    +/- 0.27C    +/- 0.44C    +/- 0.61C
1/5  DIN          +/- 0.16C    +/- 0.06C    +/- 0.16C    +/- 0.26C    +/- 0.36C
1/10 DIN          +/- 0.08C    +/- 0.03C    +/- 0.08C    +/- 0.13C    +/- 0.18C

Selecting a highly accurate sensor is only really useful, if the electronic interface is also of a sufficient accuracy, and above all if the mechanical and thermal coupling is fully mastered between the sensor and the medium to be studied, because it can introduce by itself an error of several degrees.

Pt100 sensor

Pt100 sensor   5 mm  x  2 mm

How to connect a Pt100 sensor to a data acquisition system

A platinum temperature sensor can be connected to an electronic system by the way of 3 different configurations : 2-wire, 3-wire, or 4-wire. The selection of the configuration and the selection of the electronic hardware depend entirely on the measurement accuracy which is requested for the specific plant instrumentation.

- The 2-wire configuration is the simplest one, but provides no measurement accuracy as soon as the effect induced by the electrical resistance of the wiring is of the same order of magnitude as the desired accuracy. For example and unless it is considered as a systematic error taken into account, a common 24AWG wire (85 ohms/km) will introduce a significant error of about 0.4C per meter of wiring when connected to a Pt100 sensor, but only 0.04C when a Pt1000 sensor is preferred.

- The 4-wire configuration theoretically represents the method providing the best accuracy, because the voltage is measured directly at the active part of the sensor with a high impedance interface so that the electrical resistance of the wires are no longer involved in the error of measurement. But in practice, it doesn't necessarily mean that this wiring configuration must absolutely be preferred.

- The 3-wire configuration very often ensures sufficient accuracy for medium distance wiring, and several analog or digital methods can be used to easily interface the sensor, all based on the assumption that the 3 wires have obviously pretty much the same electrical resistance. For example and also depending on the quality of the electronic interface, the use of a 18AWG wiring (21 ohm/km) quite appropriate for a medium distance may introduces an error smaller than 0.4C per 100 meters of wiring when connected to a Pt100 sensor.

2 wires Pt100 connection 3 wires Pt100 connection 4 wires Pt100 connection
2-wire Interface Example of a 3-wire Interface : VPt = V1 - 2 x V2 4-wire Interface

The main reasons for the inaccuracy of the measurement (Please refer to the french version)

The Pt100 sensor versus the Pt1000 sensor (Please refer to the french version)

Pt100 resistance/temperature calculator (Please refer to the french version)

USB acquisition modules for temperature measurement

Temperature is a very important physical parameter often taken into account in technical tests and physics experiments. TECHNETEA most often implements 3-wire Pt100 and 2-wire PT1000 interfaces in its data acquisition systems for test benches or laboratory tests, but other configurations can also be considered (4-wire connection, Pt500, etc ...) for some more specific cases.

When several different types of electronic interfaces are routed on the same Printed Circuit Board, the resulting acquisition module can also measure other physical parameters than only temperatures ; or it can even relay power to perform more complex functions as for example temperature controls. Consequently, the wide variety of possibilities leads to imagine the design of specific custom-made data acquisition modules especially compact.

Refer to : Electronic interfaces and data acquisition modules

4 x Pt100 3 x Pt100 + 1 x output 16 x Pt1000
4 inputs for 3-wire Pt100 3 inputs for 3-wire Pt100 + 1 isolated ouput 16 inputs for 2-wire Pt1000
-40C/+200C input range

Analyse temprature sonde de contact 8 x Pt1000
Thermal analysis with 8x Pt1000 sensors
Real time display software
(10 mm) Pt1000 sensor (with connector)
for contact measurement
Acquisition module with 8x 2-wire Pt1000
under development