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SS001V2
When you connect the CB400 to the mains supply it will select the insulation
0.25MΩ test position by default. Use the cursor keys to select the appropriate
function and value for the instrument to be tested.
3.1 Recording reference values for ongoing accuracy records
When using the CB400 to check an instrument for the first time it should be in
current calibration.
When the first set of tests for any instrument are undertaken.
●A separate test record sheet should be kept for each instrument.
●Each test should be repeated 3 times to establish the initial test value for
each particular instrument.
●The value obtained over the three tests should be similar and within the
instrument manufacturer’s tolerances.
●The average value over the three tests should be recorded on the
instrument test record as the Reference Value.
●It is the Reference Value which will be used for future accuracy checks on
the instrument.
3.2 Check box calibration values
Important: As there are always slight differences between the values of
components used, the actual check values of each check box are likely to vary
slightly from the nominal values on the CB400 face label.
Each CB400 is calibrated and the actual values of your individual CB400 are
shown on the calibration summary label inside the lid. It is this calibrated value
rather than the nominal value shown on the panel label that should be used
when comparing measured readings to an instrument manufacturer’s
specification.
3.3 Checking Continuity Performance
What is meant by ‘nulling’ test leads and why is it important
Continuity measurements are often made on circuits with very low resistances
with values of less than 1Ω. Most measuring instruments measure the total
resistance value between the instrument terminals including the resistance of all
connected test leads, whereas the required result is that for the circuit without
the test leads. It is therefore necessary to measure the resistance of the test
leads and deduct this value from the overall result; this is known as lead nulling.