Noise Filters; Rf Measurement Probe - IBM 5500 Operational, Installation, And Maintenance Manual

Noise Filters

RF Measurement Probe

problem. If the amplitude of this noise rises above 3 volts, it can corrupt the
data signal and cause line checks or other errors. 1 to 3 volts can cause
problems; below 1 volt will not cause problems.
This type of noise is induced into the twinax cable due to the close proximity
of power cables, heavy electrical equipment, fluorescent lamps, or due to poor
grounding of the devices connected to the twinax cable. Faulty grounding of
any device on the same power circuit as the 5500 Control Units can cause
noise to be induced. Twinax shield braiding offers a better path to ground for
RF interference than a poor utility ground on a power circuit. The ground loop
tester (if available) can detect a poor ground. Also, use a meter to verify that
the power outlets (for 5500's connected to this twinax run) have the proper
voltage and that live, neutral, and ground are wired properly.
A power line filter unit can be used to filter noise components from the utility
AC power, to suppress a known noise source as a problem determination aid,
and help reduce interference introduced into the system through the main
power circuit.
When the cable is within one building, a single station protector may also be
inserted in the twinax line. The internal capacitors in this unit offer a high
impedance to 50/60Hz, but a low impedance to twinax data signals, so they
will reduce the level of any induced 50/60Hz noise. If the cable connects two
separate buildings, a pair of station protectors are required.
Intermittent Transients
Intermittent transients are more difficult to troubleshoot. Determine the
failing devices or lines, the frequency and time of the failure. Look for a
pattern, and try to correlate the errors with something specific occurring in the
environment (machines being switched on in a factory, use of fluorescent
lamps or fluorescent lamps that are flickering, vending machines, typewriters,
dimmer controls, power short in a circuit into which units are plugged).
Check for good grounding of all devices on the power circuit. A power line
filter can reduce interference from noise that is being introduced into the
system through the main power circuit. A power line monitor can provide
useful information on the size and times of transients. Exceptionally large
transients can cause permanent damage to logic cards.
An RF probe can be used to measure high frequency current in electrical
conductors. In conjunction with a "Zapper", it can be used to determine how
quickly the system ground can dissipate RF noise.
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