From RS Pro a high-quality and reliable Pt100 PRT (Platinum Resistance Thermometer) or RTD (Resistance Temperature Detector) thin film sensing element encased in a ceramic housing or sheath. This PRT sensing element is designed to be installed into a probe sheath or other equipment and provides accurate and reliable temperature measurement for a wide range of applications.

An RTD is a type of temperature sensor based on the correlation between metals and temperature. As the temperature of a metal increases so does its resistance to the flow of electricity. This resistance can be measured and converted to a temperature reading. In a Pt100 RTD, the ’Pt’ stands for platinum (platinum wire or film) and ’100’ means that the temperature sensor has a resistance of 100 Ohms at 0°C. Platinum is the most reliable metal due to its linear resistance to temperature relationship over a large temperature range.

A thin film platinum Pt100 sensor consists of a thin layer of platinum (usually 1 micron thick) on a ceramic substrate. This is then covered with a layer of epoxy or glass for protection against high voltages and to maintain a high insulation resistance. The thin layer of platinum results in the sensor having a high resistivity and fast response times to changes in temperature. This thin film temperature sensor is enclosed in a protective ceramic sheath 35mm in length and 5mm in diameter for assembly into a housing, sheath or other equipment allowing it to be used in harsh conditions

• High stability thin film sensing element with a precision output
• IEC 60751 Class B accuracy/tolerance
• Protective ceramic sheath
• Stock numbers 237-1657 and 237-1635 have a 4 wire output for an accurate reading

These thin film PRT sensors are suitable for surface and immersion applications where protected. Their flat design means they offer a minimally intrusive means of measuring temperatures on flat surfaces. Applications and industries include the following:

• Air conditioning and refrigeration
• Chemical industry
• Plastics processing
• Stoves and grills
• Air, gas and liquid temperature measurement
• Exhaust gas temperature measurement
• Food processing
• Laboratories

The PRT temperature sensor works by placing the sensor element (or process end) into the equipment or process that requires temperature measurement. As the temperature of the platinum resistance thermometer increases it’s resistance to the flow of electricity increases. For every increase per degree of temperature the electrical resistance also changes by a set ratio, this is called the temperature coefficient. For platinum, this ratio is .00385 ohm/ohm/°C which means for a Pt100 with a 100 ohm resistance the increase in resistance per degree of temperature would be 0.385 ohms. The total resistance reading can, therefore, be measured and converted into temperature.

The resistance generated by the temperature sensor is measured by passing current through one of the wires to produce a voltage. This voltage is then measured using a suitable bridge or voltmeter and the resistance calculated in ohms using Ohm’s Law (R=V/I). Once the resistance is known you can convert it to a temperature reading using a calibration equation or a conversion table. A temperature measurement device or calibrator can also be connected to the leads of the probe that will automatically convert the measured resistance into a temperature reading.