Connections between the thermocouple or Pt100 and associated instruments may involve a physical interface with installed wiring and/or sensors. Such interfaces take the form of special connectors, terminal strips, barrier blocks and extension cables.
Due to their location in often adverse environments such as hot working zones of furnaces and machinery, temperature sensors are liable to corrosion and mechanical damage. The need for occasional replacement is inevitable and the use of suitable polarised connectors permits error-free, fast, positive and reliable interchange with no risk of dangerous cross connection.
Plugs and sockets for this purpose are produced to internationally recognised patterns, namely standard (round pin) and miniature (flat pin) versions. Ideally, connectors from the various manufacturers will interconnect directly and be fully compatible; generally, this is achieved. Many variants of the in-line connectors are produced including 3 and 4 pin versions, panel-mounting types and a wide range of multi-way panels and accessories.
Colour coding of the connector bodies is utilised to ensure clear identification of each thermocouple type since the pins and receptacles will normally be of the appropriate thermocouple alloy or compensating material; an international standard IEC584-3 1989, mod. defines these colours for thermocouples. The colour for connector bodies are expected to align with the specified colours but are not expected to be a precise match; such matching is difficult to achieve in mass production mouldings although colours to ANSI/MC96.1 presently dominate the USA markets. The use of the appropriate thermocouple alloys eliminates measurement error due to interconnection via different metals.
The connectors can be mounted directly on to the “cold end” of probes or fitted to extension cables. Good quality products should withstand up to 220°C continuous operation although some manufacturers do not offer such a high temperature rating.