Thermocouple Products

RTD

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RTD (Resistance Temperature Detector)

RTD is a temperature sensor that measures temperature by the change in
electrical resistance of platinum, which has a nominal resistance of 100 ohms at 0°C. Pt100 sensors offer higher accuracy and better long-term stability than thermocouples and are the preferred choice for precise measurement below
approximately 600°C. Thermocouple Products manufactures Pt100 RTDs in 2-wire, 3-wire and 4-wire configurations at its facility in Edenvale, Gauteng.

How It Works

  • Resistance-Temperature Relationship: The electrical resistance of platinum increases predictably and almost linearly with temperature. The instrument passes a small constant current through the element, measures the resulting resistance, and converts it to a temperature reading.
  • Why Platinum: Platinum is used because it has a high temperature coefficient, excellent reproducibility and consistency between units, and adequate resistance to chemical attack — properties no other practical metal combines as well.
  • The Pt100 Standard: "Pt100" denotes 100 ohms at 0°C. This is an internationally recognised standard, so a Pt100 element from any compliant manufacturer will read correctly on any Pt100 instrument.
  • Lead Resistance: Because the measurement is a resistance, the resistance of the connecting cable is included in the reading unless compensated. This is why wire configuration matters

Key Specifications & Features

  • Nominal Resistance: 100 ohms at 0°C.
  • Operating Temperature: Up to 600°C in 316 stainless steel, or 800°C in Inconel 600.
  • Wire Configurations: 2-wire, 3-wire and 4-wire.
  • Element Arrangements: Single, duplex and triplex — two or three independent elements in one sheath.
  • Sheath Diameters: 3 mm, 4,5 mm, 6 mm, 8 mm, 9,5 mm and 12 mm in standard construction; 3 mm and 6 mm in mineral insulated construction.
  • Insertion Lengths: 50 mm to 2 000 mm in standard construction; 100 mm to 1 000 mm in mineral insulated construction.
  • Accuracy & Stability: Higher accuracy and significantly better long-term stability than a thermocouple, with minimal drift over repeated thermal cycling.
  • Customisation: Any length, sheath diameter, wire configuration, termination and process fitting manufactured to order.

Common Applications

  • Food & Beverage Processing: Pasteurisation, cooking, chilling and cold storage, where accuracy directly affects product safety and regulatory compliance.
  • Pharmaceutical Manufacturing: Reactors, autoclaves, clean rooms and storage, where validated, stable measurement is a regulatory requirement.
  • HVAC & Building Services: Air handling, chilled water and hot water systems, where 3-wire Pt100 sensors are the industry norm.
  • Chemical Processing: Reactor vessels, heat exchangers and distillation columns operating below 600°C, where thermocouple drift would be unacceptable.
  • Laboratory & Calibration: Reference measurement and instrument calibration, typically using 4-wire configurations for maximum accuracy.
  • Water Treatment & Utilities: Process water, effluent and boiler feedwater monitoring, where long-term stability reduces recalibration frequency.

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