Quantcast Section 4: Electrical Test Equipment

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General. This section describes several types of electrical test equipment used for
maintenance of lighted navigational aid equipment. The test equipment is listed in order of
relative usefulness. For maintenance purposes, it is recommended that every facility acquire at
least a volt-ohm-milliammeter and an insulation tester. These two units are required for many
maintenance routines and are useful for troubleshooting. Operating instructions for the
equipment listed are contained in the manufacturer's manual supplied with the equipment.
Periodic condition checks should be performed on all test equipment to ensure safe operation.
General. The volt-ohm-milliammeter (VOM), Figure 3 is a highly versatile piece of
test equipment that is capable of measuring AC/DC voltages, resistance, and low values of DC
current. The VOM is particularly useful for checking control circuit voltage and checking the
continuity of circuit components. These readings help isolate the problem when troubleshooting.
Safety. Safety must always be considered when using the VOM. Know the voltage
levels and shock hazards related to all equipment to be tested. Be sure that the VOM has been
tested and calibrated. Portable test instruments should be inspected and calibrated at least once a
year. Check the condition of the VOM test leads before making any measurements. General
safety recommendations for specific uses of a VOM are contained in the manufacturer's manual
supplied with the equipment.  High-Voltage Measurements. Never try to take direct voltage readings on power
distribution circuits rated over 600 volts. Measurement of high voltage is accomplished by
installing instrument transformers and meters.  Switch Settings. When making voltage measurements on power and control circuits,
be sure that the meter selector and range switches are in the correct position for the circuit being
tested before applying test leads to the circuit conductors. To prevent damage to the meter
movement, always use a range that ensures less than full-scale deflection of the pointer. A 1/3-
to-midscale deflection of the pointer ensures the most accurate reading.  Case Insulation. Do not hold the VOM in the hand while taking the reading. Support
the instrument on a flat surface. If holding the VOM is unavoidable, do not rely on the insulation
of the case.


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