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imc C-SERIES - Manual, Version 4 R 3 - 2018-10-19

121CS-7008-FD, CL-7016-FD

5.8.4.1.2 Thermocouple mounted without ground reference

The thermocouple is installed with electrical isolation from the device's Ground / Chassis and is therefore

not connected with the device's ground. This is achieved by, among other techniques, having the

thermocouple adhere to non-conducting material. As a result, the thermocouple's voltage floats freely

against the amplifier ground voltage.

In this case, the amplifier must provide the necessary ground potential.

Thermocouple measurement without

ground reference

In the operating software, activate "Isolated thermo couple" at the amplifier tab. In this measurement

mode, the unit itself provides the ground reference by having Terminals -IN and -VB connected internally.

This connection is only made in the Thermocouple mode and not with voltage measurements.

Warning: The thermocouple itself may not be ground referenced!

If it was mounted with a ground reference, there is a danger that a large compensation current will flow

through the thermocouple's (thin) line and the connector plug. Compensation currents are a danger

with every single end measurement. For that reason, single end measurement is really only allowed -

and only then really necessary- if the thermocouple has no ground reference of its own.

5.8.4.2 PT100/ RTD measurement

Along with thermocouples, PT100 can be connected directly in 4-wire-configuration (DSUB-plug:

ACC/DSUBM-UNI2). The 4-wire measurement returns more precisely results since it does not require the

resistances of both leads which carry supply current to have the same magnitude and drift. Each sensor is

fed by its own current source with approx. 1.2 mA.

IMC C SERIES User Manual

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