© Isothermal Technology
Page 59 of 102
923 milliK manual - issue: 1.10
4
5
6
1
2
I-
I+
V+
V-
3
NC
NC
It is important that none of the current flowing between I+ and I- flows along the short circuit
between V+ and V-. There should only be a single link between the voltage and current
circuits, as shown.
5.1.2 Making a 0mV Source in a Thermocouple Connector
A 0mV source is essentially a piece of copper wire that can be connected across the
thermocouples inputs of the milliK. However, you need to take care in making this short
circuit in order to avoid creating thermal EMFs that are significant for an instrument as
sensitive as the milliK.
The best method for making a 0mV source is to take a copper miniature thermocouple plug
and short together the two pins of the connectors with a short length of copper wire. The
copper wire should remain inside the connector housing, be as short as possible and go
directly between the two terminals of the connector. Ideally, the wire used should be high
purity copper, but single stranded copper wire (tinned, plated or unfinished) will provide
adequately low thermal EMFs in this arrangement. Using a longer (even just 15mm in length)
piece of normal wire that goes outside the connector housing can produce measurable thermal
EMFs.
5.2 Checking the Calibration
The calibration of the milliK can easily be checked by attaching reference standards
(calibrated resistors, voltage source or current source) to the milliK and measuring their
values. Typically you would check the following:
0
Ω
reading on the 115
Ω
range
100
Ω
reading on the 115
Ω
range
400
Ω
reading on the 460
Ω
500k
Ω
reading on the 500
Ω
0mV on the 115mV range
