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Many
faults can cause control circuits to cut out through a safety
trip in the system. This can result in the system, or part of
the system, ceasing to operate. When
this sort of thing happens, many inept engineers like to press
reset buttons, make (unnecessary) adjustments to equipment and
safety devices, operate contactors by hand etc., often seemingly
at random.
However,
a structured approach to these problems would allow an engineer
to save himself an enormous amount of time, and to make proper
and long-lasting repairs to a system without inducing other faults.
All that are needed are a few
basic rules to allow you to quickly
determine which electrical component (security device or otherwise)
has failed.
Instead
of asking himself "what could be defective?" and searching
for the fault by a process of guesswork, a competent engineer
once he's (quickly) identified a fault should ask himself: Why
has this safety device tripped, and what can be done to stop it
happening again? He will find the time to perform a general inspection
of the installation and will be able to foresee recurring faults.
This
sort of attitude will be beneficial to everyone, including the
client, the engineer and the business.
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EXERCISE
1
: The
fuse FL has blown. All
other components are OK.
What
would the reading be on a voltmeter connected between 1 and 2
with the switch 's' open? And with the switch 's' closed?
EXERCISE
2
: The fuse
FL has blown. All the other components are OK. What would
the reading be on a voltmeter connected between 3 and 4 with the
switch 's' open? And
if, in addition, the coil R is broken, what
would the voltmeter read when connected between 3 and 5 (switch
's' open, and switch 's' closed)?
EXERCISE
3
: The coil R
is broken. All
the other components are OK.
What would the reading be on a voltmeter connected between 6 and
7 with the switch 's' open? And if the switch 's' is closed?
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