8000 SERIES OPERATION MANUAL TRANSMILLE LTD.
TRANSMILLE LTD. PAGE 56
Getting the best out of the multimeter.
The 8000 series are accurate multimeters measuring a very wide range of input 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.
Power line and low frequency Pick up and noise
These effects are most noticeable when using high resistance (100kohms and above) and low
current. All constant current sources have a very high output impedance which will pick up noise just
like the high value resistance . To reduce pickup, use screened leads and try earthing the low side of
the multimeter output.
For high value resistance it is essential that the cables insulation resistance will not effect the
accuracy. Most PVC cables will only have insulation resistance of around 10GΩ, this will give an
error of 1% on the 100mohm output.
Low AC Current is particularly difficult as the capacitance of screened leads will shunt some of the
current away.
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