B&K Precision 1655A - Manual - Manual (Page 23)

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VARIABLE VOLTAGE SOURCE
Both the Model 1655A and 1653A AC Power Supplies offer
continuously variable output voltage from 0 to 150VAC. Several
applications are listed below, but the versatile instruments may be
used in any application where an ac power source of any value
from 0 to 150 volts is required, and within the maximum current
rating of the instrument.
24 VOLT APPLICATIONS
Class II industrial control equipment operates from nominal 24
volt, 60 Hz ac power. Such equipment is widely used in
industrial plants. These power supplies can be adjusted to 24
volts ac for bench servicing of the equipment.
130-150 VOLT APPLICATIONS
The ability to go higher then 130 volts is indispensable in
component and equipment testing where specifications must be
exceeded to verify designs and overvoltage margins.
TROUBLESHOOTING EQUIPMENT THAT BLOWS
FUSES
One of the problems with troubleshooting equipment with a
severe overload or short is that it repeatedly trips its circuit
breaker or blows fuses. Full power cannot be applied long
enough for normal voltage and waveform measurements to be
performed. The variable voltage feature permits operation at a
lower voltage that does not activate the protective device; testing
and troubleshooting can be performed with power applied.
Using the Model 1655A or 1653A AC Power Supply as shown
in Fig. 10, voltage can be set to 0 volt and slowly increased while
monitoring the current. Problems such as a defective circuit
breaker that open too soon are quickly spotted. If current reaches
its normal value (typically, about 70% of the fuse of protective
device rating) at a low voltage such as 20 volts, there is a major
short in the power supply or one of the main power distribution
circuits. If current increases to its normal value more gradually,
allowing voltage to approach 100 volts or more, an overload in
one of the circuits is probably the cause. Current that increases
sharply above a certain voltage may indicate electrical breakdown
or arcing within a component. Voltage or current measurements
in various circuits (see Fig. 10) while varying the input voltage
can help isolate the fault.
INPUT VOLTAGE SPECIFICATION TESTING
Most ac powered equipment is specified to operate over a
range of input voltage such as 120VAC ±10%. Complete
performance testing cannot be conducted without a variable ac
source. Some testing may merely consist of measuring regulated
dc voltages while varying the ac source voltage; with other tests
conducted at nominal line voltage.
LOW OR HIGH LINE VOLTAGE RELATED FAILURES
Occasionally, an equipment malfunctions only during
conditions of low or high line voltage. Troubleshooting of such
problems is almost impossible without a variable ac voltage
source. Either Model 1655A or 1653A AC Power Supply serves
as a variable ac voltage source.
OPERATING INSTRUCTIONS Troubleshooting: Use As Variable Voltage Source
TROUBLESHOOTING: USING THE AC POWER SUPPLY AS A VARIABLE AC VOLTAGE SOURCE