Application Notes on Thermocouple Transmitters.

Thermocouple temperature transmitters convert the small millivolt (mV) output of a thermocouple to a current signal (typically 4-20 mADC) that is immune to noise and voltage drops over long distances. They are used with thermocouple temperature probes, bimetallic devices that are suitable for various temperature sensing applications. Isolated thermocouple temperature transmitters eliminate ground loop problems by isolating the transmitter input from the transmitter output. Output options include analog current, analog voltage, or relay/switch output.
Metal type is an important consideration when selecting thermocouple temperature transmitters. Base metal thermocouples can measure different temperature ranges, depending on the sensor material. Each type or designation represents a specific metal type and temperature range. Type E (chromel/constantan) has a typical temperature range of -270° C to 1000° C. Type J (iron/constantan) has a temperature range of -210° C to 1200° C. Type K (chromel/alumel) has a temperature range of -270° C to 1372° C. Type N (nicrosil/nisil) has a temperature range of -270° C to 1300° C. Type T (copper/constantan) has a temperature range of -270° to 400° C. For noble and refractory metals, choices include type B (platinum 30%/rhodium) with a temperature range of 0° C to 1820° C; Type S (platinum 10%/ rhodium) with a temperature range of -50° C to 1768° C; Type R (platinum 13%/rhodium) with a temperature range of -50° C to 1768° C; and Type W (tungsten/rhenium) with a temperature range of 0° C to 2300° C.
Performance specifications for thermocouple temperature transmitters include analog voltage, analog current, resistance, and temperature. Devices that receive analog voltage inputs accept and condition voltage inputs such as 0 – 10 VDC. Devices that receive analog current inputs accept and condition current loops such as 4 – 20 mA. Devices that receive resistance inputs accept and condition analog resistance inputs such as 0 to 10 ohms. For thermocouple temperature transmitters, operating temperature is a full-required range.
There are several mounting styles for thermocouple temperature transmitters. Devices with thermohead/thermowell mounting are designed to be an integral part of a probe assembly. Some devices are suitable for mounting on a DIN rail. Others are designed to be mounted within a cabinet or rack. Thermocouple temperature transmitters that mount on computer boards are also available.

Sebastian

G.M. Technical

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