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338 Keysight 34970A/34972A User’s Guide
Relay Life
As a relay is used, the contacts begin to wear and the resistance of the closed
contacts increases. The initial contact resistance of a relay is typically 50 mΩ (plus
lead resistance). When the contact resistance exceeds 20 to 50 times its initial
value, the contact resistance becomes very erratic and the relay should probably
be replaced. For most applications, a relay with contact resistance greater than
1Ω should be replaced. The graph below shows the typical contact resistance
characteristics of the relays used on the 34970A/34972A switching modules.
Relay Load
For most applications, the load switched by the relay is the most important factor
affecting relay life. As shown in the graph below, relay life is maximized by
switching low power. As the power switched increases, relay life deteriorates.
1k 10k 100k 1M 10M 100M
0Ω
1Ω
Typical Relay Lifetime
Relay Operations (Cycles)
Relay Contact
Full Load Typical Signals No Load
Maximum Switching Capacity
Voltage Switched
300V
240V
180V
120V
60V
0.2A 0.4A 0.6A 0.8A 1A
10 mA 20 mA 30 mA 40 mA 50 mA Reed (34902A)
Armature (34901A, 34903A, 34904A,34908A)
Current Switched
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