Transmille 1000-Series - Manual (Page 95)

1000 SERIES OPERATION MANUAL
TRANSMILLE LTD. Version 1.30 Page 95
Getting the best out of the calibrator.
The 1000 series are very accurate calibrators producing a very wide range of output
signals. To make the best possible use of the range of outputs and to eliminate
errors this section details some common sources of errors and offers some
techniques to reduce them.
Thermally generated EMF voltage errors.
At every connection in a measuring system different metals come into contact with
each other, each junction forms a thermocouple. The voltages generated at these
junctions are called thermoelectric voltages and are dependent on the type of metals
in contact and the difference in temperature.
This effect, of course, is used to measure temperature with thermocouples, however
this effect will cause large errors in low voltage measurements, as thermocouple
voltages for some metals can be in the millivolt region. Copper is best but many
standard test plugs are made from nickel plated brass and should not be used.
Gold plated copper plugs are available for low level work. If the test lead has been in
use on a high current range this will have made the plug warm, which will also
increase the error.