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Chapter 11 Special Procedures
Noisy Readings
In general, noisy readings are caused by poor connections either to the input terminals or to the test
load. If noisy readings are encountered, check these connections first.
Inductive Loads
The measurement of highly inductive loads (such as large transformers) may also yield noisy readings.
This is due to the very high impedance to line voltage exhibited by the load causing an excessive
amount of noise pick-up. This effect can be significantly reduced by using fully shielded cables. It may
also be helpful (and will cause the settling time to be reduced) if the unused windings on transformers
being tested can be short- circuited during the measurement. This will significantly reduce the
inductance of the winding under test and will also prevent these windings from producing dangerous
voltages during connection and disconnection of the ohmmeter.
Drifting Displays
All Valhalla ohmmeters use a high impedance voltmeter as part of the resistance measurement process.
This voltmeter is a highly accurate and stable 4½ digit analog-to- digital converter (A to D). Unless it is
receiving a definite input signal, the output display of this A to D is ambiguous. The display may
indicate a randomly wandering number, or it may flash indicating an overrange condition. This
unpredictable display may make it seem to appear that the instrument is experiencing some sort of
malfunction. It is, in fact, just a characteristic of the voltmeter circuit and should not be mistaken for a
fault in the instrument.
The display indications should be ignored unless there is a definite measurement being taken. If this
wandering display is not acceptable, the ohmmeter can be made to indicate an overrange condition
whenever the terminals are opened either by using a 4-wire Kelvin type lead set (Valhalla Option "K")
or by shorting the V
HI
and I
HI
terminals together.
The display should indicate a stable reading when the test leads are securely attached to the device
under test. If the display appears to be erroneous when connected to a load, recheck the test leads for
integrity and cleanliness. If all external items appear to be functioning properly, the problem may be
the ohmmeter. In this case, please call the factory.
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