User`s guide

321
Chapter 7 Tutorial
Relay Life and Preventive Maintenance
4
7
Relay Life and Preventive Maintenance
The 34970A/34972A Relay Maintenance System automatically counts the
cycles on each relay in the instrument and stores the total count in non-
volatile memory on each switch module. Use this feature to track relay
failures and predict system maintenance requirements. For more
information on using this feature, refer to “Relay Cycle Count” on page
169.
Relays are electromechanical devices which are subject to wear-out
failure modes. The life of a relay, or the number of actual operations
before failure, is dependent upon how it is used – applied load, switching
frequency, and environment.
You can use the graphs shown in this section to estimate relay lifetimes
for your application. Additional background information is also provided
to give you a better understanding of relay wear-out mechanisms. In
general, relay lifetimes depend heavily upon the signals that are being
switched and the types of measurements being performed.
• Switching typical signal levels will result in relay lifetimes from
1,000,000 to 10,000,000 operations.
• High-power switching (>25% rating) or high-voltage switching
(>100V) applications will yield relay lifetimes from 100,000 to
1,000,000 operations.
• Low-voltage switching (<30V) and low-current switching (<10 mA)
applications will yield relay lifetimes to 10,000,000 operations.
• RF switching applications seldom exhibit relay lifetimes exceeding
1,000,000 operations due to more stringent contact resistance
requirements (typically less than 0.2).
The following table shows the time required to reach the specified
number of switch operations for several switching speeds.
Continuous
Switching Speed
Switching Operations
100,000 1,000,000 10,000,000
1 / Hour
1 / Minute
1 / Second
10 / Second
12 Years
10 Weeks
1 Day
3 Hours
2 Years
12 Days
1 Day
4 Months
12 Days
34970A Refresh UG.book Page 321 Wednesday, February 17, 2010 12:34 PM