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Chapter 7 Tutorial
Relay Life and Preventive Maintenance
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7
Switching Frequency
Relay contacts heat up as they switch significant power. The heat is
dissipated through the leads and the body of the relay. As you increase
the switching frequency to near its maximum, heat cannot dissipate
before the next cycle. The contact temperature rises and the life of the
relay is reduced.
Replacement Strategy
There are essentially two strategies that you can use for preventive
maintenance of the relays on the switching modules. The strategy that
you choose depends upon your application, the consequences of a relay
failure in your system, and the number of relay cycles during a
measurement session.
The first strategy is to replace each relay as needed after it fails or
becomes erratic. This is suitable if you are switching higher loads on only
a few relays on the module. The disadvantage of this strategy is the
inconvenience of continually replacing relays as they near the end of
their life at different times.
The second strategy is to replace all relays on the module or simply
purchase a new module as the relays near the end of their life. This
strategy is best suited for those applications where all relays on the
module are switching similar loads. The failure of several relays over a
relatively short period of time may indicate impending failures on other
relays switching similar loads. This strategy decreases the risk of failure
during actual use at the expense of replacing some relays that may have
useful life remaining.
Note : In both cases described above, you can use the 34970A/34972A
Relay Maintenance System to track and even predict relay failures.
34970A Refresh UG.book Page 323 Wednesday, February 17, 2010 12:34 PM