Keysight VXI Bus 75000 C Series, Руководство по обслуживанию

Страница: 10 / 62

12 Keysight E1463A 32-Channel Form C Switch Service Guide
General Information Relay Life
Relay Life
Electromechanical relays are subject to normal wear-out. Relay life depends on
several factors. The effects of loading and switching frequency are briefly
discussed below:
Relay Load. In general, higher power switching reduces relay life. In addition,
capacitive/inductive loads and high inrush currents (e.g., when turning on a lamp
or motor) reduce relay life. Exceeding the specified maximum inputs can cause
catastrophic failure.
Switching Frequency.
Relay contacts heat up when switched. As the switching
frequency increases, the contacts have less time to dissipate heat. The resulting
increase in contact temperature reduces relay life.
End-of-Life Detection
A preventive maintenance routine can prevent problems caused by unexpected
relay failure. The end of the life of a relay can be determined using one or more of
the three methods described below. The best method (or combination of
methods), as well as the failure criteria, depends on the application in which the
relay is used.
Contact Resistance. As the relay begins to wear out, its contact resistance will
increase. When the resistance exceeds a pre-determined value, the relay should
be replaced. Typically, a relay should be replaced when the contact resistance
exceeds 2.0 Ohm.
Stability of Contact Resistance.
The stability of the contact resistance decreases
with age. Using this method, the contact resistance is measured several (5-10)
times, and the variance of the measurements is determined. An increase in the
variance indicates deteriorating performance.
Number of Operations. Alternatively, relays can be replaced after a predetermined
number of contact closures. However, this method requires knowledge of the
applied load and life specifications for the applied load. For the Keysight E1463A,
maximum relay life is specified at 5 X 107 operations with no load and 3.5 X 104
operations at the worst-case rated load.
Replacement Strategy
The replacement strategy also depends on the application. If some relays are
used more often, or at higher load, than the others, the relays can be individually
replaced as needed. If all of the relays see similar loads and switching
frequencies, the entire circuit board can be replaced when the end of life
approaches. The sensitivity of the application should be weighed against the cost
of replacing relays with some useful life remaining.