IMC CANSAS - Page 420

420 Properties of the Modules
imc CANSAS Users Manual - Doc. Version 1.9 - 05.12.2014© 2014 imc Meßsysteme GmbH
6.20.4.1.2 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 CANSAS operating software, select the measurement mode "Thermocouple (mounted without
ground reference)".
In this measurement mode, the UNI8 unit itself provides the ground reference by having Terminals B and
D connected internally. Then a measurement which is practically single-ended (ground-referenced) is
performed. There is no disadvantage to this if there was no ground reference previously.
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. This can even lead to the destruction of
the amplifier. 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.