©Isothermal Technology
Page 32 of 61
914 millisKanner manual Iss. 1.00
5
5
5
5
The millisKanner Technology
The millisKanner Technology
The millisKanner Technology
The millisKanner Technology
The millisKanner uses a number of new technologies and measurement techniques to
achieve performance and ease of use that have not previously been available with similar
multiplexers.
5.1
5.1
5.1
5.1
Minimising Thermal EMFs
Minimising Thermal EMFs
Minimising Thermal EMFs
Minimising Thermal EMFs
Thermal EMFs (EMFs generated when circuits comprising dissimilar metals are exposed
to temperature gradients) are a potential source of error when working at this precision.
These can be eliminated when measuring resistance thermometers by reversing the
current and averaging the measurements (the offsets in the two measurements cancel
each other out when the readings are averaged together). However, this technique cannot
be used when measuring the voltage generated by thermocouples, so the thermal EMFs
need to be eliminated at source. For this reason, we use tellurium-copper (gold plated)
as the thermocouple connector contact material, since this combines good mechanical
properties with extremely low thermal EMFs against the copper terminations of a
thermocouple.
In order to eliminate thermal EMFs from the measurement system (already small), the
input connections are reversed between the input and output terminals of the
millisKanner. Measurements made with and without the reversal are then averaged
together to eliminate the thermal EMFs generated in the connectors and cables used to
connect the millisKanner to the milliK. The limitation is then the thermal EMFs generated
by the devices used to implement this reversal.
The millisKanner duplicates the reversal system used by the milliK. It detects that it is
making a measurement via a millisKanner, and then makes the reversal in the
