User manual
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. The end-of-life resistance recommended by
Agilent Technologies can be found in Appendix A of the Agilent E1460A
User’s Manual.
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.
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.
Note
Relays that wear out normally or fail due to misuse should not be
considered defective and are not covered by the product’s warranty.
10 General Information Agilent E1460A Service Manual