From RS Pro a high-quality and reliable Pt100 PRT (Platinum Resistance Thermometer) or RTD (Resistance Temperature Detector) sensing probe. This RTD probe has a robust construction with the sensing element encased in a rigid 316 stainless steel sheath and a bayonet fitting feature. The leads have a durable fibreglass insulation and are covered with a rugged stainless steel overbraid. This platinum resistance thermometer 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.

The probes of these Pt100 sensors have an adjustable screw threaded stainless steel spring 250 mm long with a slotted bayonet fixing cap. The bayonet cap screws along this spring and allows the immersion length of the sensor probe to be adjusted. Once in place, the bayonet cap is secured to a bayonet adapter (which must be purchased separately allowing the temperature sensor to be firmly held in place within the recess. The other end of the probe is terminated by 3 insulated wire tails which are connected to the temperature measuring equipment.

• High stability sensing element with a precision output
• IEC 60751 Class B accuracy/tolerance
• Adjustable bayonet fitting
• Rigid 316 corrosion resistant stainless 6mm diameter steel sheath for protection of sensing element
• Leads with durable fibreglass insulation and a rugged stainless steel overbraid
• 3 lead wires for an accurate reading

These bayonet style PRT sensors are designed for direct installation into the process. The bayonet fitting makes them suited for applications where the probe tip is fitted directly into a drilled hole or recess in machinery.

• 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 Pt100 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.