SECTION IX SPECIAL PROCEDURES
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9-1. General
This section contains a number of useful tips that should be noted when working with inductive loads.
Inductive loads include devices such as transformers, coils, ballasts, wire-wound resistors, magnets and
motors. These types of devices require special consideration as described below.
9-2.
Connections and Settling Time
When connecting the cables to the inductive load, care should be taken not to draw an arc. The Test Current
should be turned Off and the cables positively clamped onto the load before applying current.
When measuring highly inductive loads the settling time of the ohmmeter is determined by the compliance
voltage of the current source. Typically, the compliance voltage of a 4300B in the Charging Inductor mode is
in excess of 20 volts. Thus, with an inductor of 1000 Henries (an extremely large transformer) the unit will
take approximately 10 minutes to settle. During settling, the unit will display overload and should be ignored
until the Charging Inductor indicator is extinguished.
The actual equation for determining settling time is as follows:
T = (L x I)/V
Where:
T = settling time in seconds
L = inductance in Henries
I = current range (in amps)
V = compliance voltage of 4300B (20V)
Note that the higher the test current, the longer the settling time.
9-3. Noisy
Readings
When measuring very low resistances of highly inductive loads, care should be taken to reduce 60Hz pickup
at the input to the 4300B. The noise pickup is caused by the very high impedance of the load at 60Hz given
by the formula:
Z = 377 x L
Where:
Z = Impedance in ohms
L = Inductance in Henries
