T6V4 Channel 5 and 6 Input Setup with Thermocouple Leads
SYMPTOMS
Thermocouple results on channels 5 and 6 are outside the specification tolerance range.
SOLUTION
Channels 5 and 6 on the T6V4 data logger are 'shared' channels and can be used to measure both temperature and voltage. Because of the module circuit design to accommodate this feature, inputs 5 and 6 are low impedance, approximately 30 kW (30 kilohms). The other temperature channels are nominally 1 MW (1 megohm).
This low impedance means channels 5 and 6 are affected by the resistance of the thermocouple leads and the temperature being measured. Under these conditions the data logger may produce results outside the tolerance range quoted in the specification.
Channels 5 and 6 may also produce out-of-tolerance readings with voltage connected to these inputs even if the data logger is set to read temperature. Page 23 of the Owner's Manual refers to both these conditions under the 'WARNING' section:
'Thermocouple channels 5 and 6 have a low input impedance due to the fact that they are shared with the voltage channels 9 and 0. If thermocouples of a resistance higher than a few ohms (e.g. thermocouples with wire lengths longer than typically 2 to 3 meters) are used in these channels a small error will be introduced. This error is proportional to the ratio of the thermocouple resistance to the input impedance.'
FAQ ID: 11620 Last Reviewed: 27 September 2005