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Surface-Mount Thermocouples

Surface-mount thermocouples are used when equipment cannot be penetrated. Measuring refrigerant temperature is an example of appropriate surface-mount thermocouple usage; there is no reasonable method for immersing a thermocouple in the refrigerant flow path. Surface-mount thermocouples are also used to measure solid surface temperatures. In the case of measuring refrigerant temperature, the temperature of the solid surface is being measured, and care must be taken to ensure it is the same temperature of the underlying refrigerant in the example above.

Types

Surface-mount thermocouples come in two varieties. The pre-formed type with bonding material can be used directly. Alternatively, if you solder your own thermocouple wire into an on-site thermocouple, be sure to calibrate it using both boiling and ice water, against a known (manufactured) thermocouple.

Installation

Surface-mount thermocouples may be mounted using a bonding material, or with mechanical means. The bonding material is usually an epoxy material or glue. The surface must be relatively clean and free of dirt, dust, and oil for the bonding to be reliable. Emery cloth can be used to buff a small spot clean prior to bonding. Mechanical methods of fastening include pipe clamps and electrical tape.

Isolation

Because surface-mount thermocouples are exposed to the surrounding environment, they often need to be isolated. Sunshine, air flow, and nearby heat sources can significantly affect these measurements. Therefore it is best to place insulation over all surface-mount thermocouples. For pipe-mounted thermocouples, usually an 8-12" length of pipe insulation is sufficient. The insulation should be chosen to prevent conductive, convective, and radiant heat transfer from affecting the measurement. Pipe insulation and spray foam are two methods to insulate surface-mount thermocouples.

It may also be necessary to protect the thermocouple from corrosion, such as in outdoor environments. This is only necessary for long-term monitoring.