Reference Multimeter and 8 ½ Digit Multimeter
Guidelines to Avoid Measurement Errors
125
Guidelines to Avoid Measurement Errors
To avoid errors, see Table 25.
Table 25. Guidelines to Avoid Errors
Sources of Inaccuracy Avoiding or Minimizing Inaccuracy
Thermal EMFs can cause series (Normal) mode
interference, particularly where large currents
have a heating effect at junctions. In otherwise
thermoelectrically-balanced measuring circuits,
cooling caused by drafts can upset the balance.
Screen thermal junctions from drafts.
• Before taking readings allow time for thermal
equilibrium to be reached.
• Use conductors, joints and terminals with a
good margin of current-carrying capacity.
• Avoid thermoelectric junctions where
possible:
o Use untinned single-strand copper wire of
high purity.
o Avoid making connections through Nickel,
Tin, Brass and Aluminum. If oxidation is a
problem, use gold-plated copper
terminals, and replace the terminals
before the plating wears off.
o If joints must be soldered, low-thermal
solders are available, but crimped joints
are preferred.
o Use low-thermal switches and relays
where they form part of the measuring
circuit.
o Balance one thermal EMF against another
in opposition, where possible. (Switch and
relay contacts, terminals, etc.)
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