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| A Thermocouple is a
temperature measuring device consisting of two conductors
of dissimilar metals or alloys that are connected only at
the ends. When the ends are at different temperatures a
small voltage is produced in the wire that can be related
directly to the temperature difference between the ends.
If the temperature at one end is known, the temperature
at the other end can be determined. Thermocouple wire or extension grade wire is recommended to be used to connect thermocouples to the sensing or control instrumentation. The conditions of measurement determine the type of thermocouple wire and insulation to be used. Temperature range, environment, insulation requirements, response, and service life should be considered.
Type J (Iron vs Constantan(TM)) is used in vacuum, oxidizing, inert or reducing atmospheres. Iron element oxidizes rapidly at temperatures exceeding 1000ºF (538ºC), and therefore heavier gauge wire is recommended for longer life at these temperatures. Type K (CHROMEL®* vs ALUMEL®*) is used in oxidizing, inert or dry reducing atmospheres. Exposure to vacuum limited to short time periods. Must be protected from sulfurous and marginally oxidizing atmospheres. Reliable and accurate at high temperatures. Type T (Copper vs Constantan(TM)) is used for service in oxidizing, inert or reducing atmospheres or in vacuum. It is highly resistant to corrosion from atmospheric moisture and condensation and exhibits high stability at low temperatures; it is the only type with limits of error guaranteed for cryogenic temperatures. Type E (CHROMEL®* vs Constantan(TM)) may be used in oxidizing, inert or dry reducing atmospheres, or for short periods of time under vacuum. Must be protected from sulfurous and marginally oxidizing atmospheres. Produces the highest EMF per degree of any standardized thermocouple. Type N (Nicrosil(TM) vs Nisil(TM)) is used in oxidizing, inert or dry reducing atmospheres. Must be protected from sulfurous atmospheres. Very reliable and accurate at high temperatures. |
| Thermocouple wire can be fabricated into an accurate and dependable thermocouple by joining the thermoelements at the sensing end. | Thermocouple wire or thermocouple extension wire of the same type must be used to extend thermocouples to indicating or control instrumentation. RED color code is negative throughout circuit. | Hook-up Red Color-Coded wire to negative terminal of instrument. |
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| Temperature limit of the thermocouple depends on the thermocouple wire: wire size; wire insulation; and environmental factors. | Use thermocouple connectors if required, they are made of the same alloys and have the same color codes as extension wire. (Except Hi-Temp connectors are all colored red regardless of T/C type.) PMC thermocouple connectors are molded from strong, non-melting, glass filled thermocouple compounds. | |
| NOTE: * CHROMEL® and ALUMEL® are registered rademarks of Hoskins Manufacturing Company. PMC Corporation reserves the right to substitute equivalent product to CHROMEL® and ALUMEL® at any time. |
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