ROC827 Instruction Manual

DOC0512B

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J OR K THERMOCOUPLE

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UNGROUNDED SHEATH

 

Figure 4-15. Type J and K Thermocouple Wiring

Be sure to use the correct type of thermocouple wire to connect the thermocouple to the ROC827. Minimize connections and make sure connections are tight. If you use any dissimilar metals (such as copper wire) to connect a thermocouple to the ROC827, you can create the junction of dissimilar metals that can generate millivolt signals and increase reading errors.

Ensure any plugs, sockets, or terminal blocks used to connect the extension wire are made from the same metals as the thermocouples and observe correct polarity.

The thermocouple probe must have sufficient length to minimize the effect of conduction of heat from the hot end of the thermocouple. Unless there is insufficient immersion, readings will be low. It is suggested the thermocouple be immersed for a minimum distance equivalent to four times the outside diameter of a protection tube or well.

Use only ungrounded thermocouple constructions. Grounded thermocouples are susceptible to the creation of ground loops. In turn, ground loops can cause interaction between thermocouple channels on the thermocouple module.

Note: Use thermocouples as individual sensing devices. All modules are isolated on the field side. Be aware that you can induce ground loops by tying module-to-module commons together.

Issued Mar-06

Input/Output Modules

4-18

Page 88
Image 88
Emerson ROC827 instruction manual Type J and K Thermocouple Wiring