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placed in areas where a high electromagnetic field
strength exists. Leading causes of interference include
AM and FM radio station transmitters, television station
transmitters, induction heaters, and motors (with
commutators) of 0.25 horsepower (200 watts) or greater.
Small tools with universal motors are generally not a
problem when they operate on separate power lines.
Motors without commutators generally do not cause
interference.
Field strengths below 2 volts per meter are unlikely to
cause interference. Field strength can be measured by a
tunable meter such as the Model R-70 meter manufactured
by Electro-Metrics Division, or broadband meters such as
the HOLADAY™ HI-3001 meter or Model EFS-1 meter
manufactured by Instruments for Industry, Inc.
You can estimate the field strength produced by radio
transmitters by dividing the square root of the emitted
power in kilowatts by the distance from the atenna in
kilometers. The result yields the approximate field
strength in volts per meter and is relatively accurate for
distances greater than about half a wavelength (150 meters
for a frequency of 1000 KHz).
Solutions to Radio-
To reduce or eliminate radio-frequency interference
Frequency
problems from nearby induction heaters or 0.25
Interference Problems
horsepower motors, either move the equipment causing
the problem or move the MERLIN II system control unit
to a different location.
To reduce or eliminate radio-frequency interference
problems from nearby radio station antennas, choose from
among the following solutions:
●
Do not run MERLIN II system station wire in the same
conduit as ac cable, or next to ac circuits if the station
wire is exposed. If possible, do not cross station wire
2-10 System Grounding Requirements