Relay Maintenance Report For National Instruments Switches

When selecting a relay for an application an important characteristic to be considered is its life expectancy. Contact of mechanical relays wear with usage, and worn contacts have a higher contact resistance. Relay life is specified as a minimum number of cycles before its contact resistance exceed a certain value. When this value is exceeded, the relay is past its useful life time. One cycle is defined as the action of opening and closing the relay. The expected life is divided into two main categories: mechanical and electrical.

Mechanical life
The mechanical lifetime specification is typically the number of switch cycles before the contact resistance rises above a specific value assuming no electrical load across contacts during actuation.

Electrical life
Switching active electrical signals, especially high power signals causes arcing across the relay contacts. This arcing produces pits on the contact surface and accelerates the contact wear. The electrical life specification is the number of switch cycles, under load, before the contact resistance rises above a certain value.


Relay Maintenance
National Instruments implemented a new feature for all switches modules released after May 2003 that tracks relay usage for all relays on a switch module. This feature is accessible using the NI-SWITCH API and NI-DAQmx API using niSwitch get relay Count and DAQmx Switch Get Relay Count respectively. This function requires a relay name and returns its number of cycle.
For you convenience, a program is available at this location: Switch Maintenance Report Programs.
The programs are written in LabVIEW and generate a report that lists all NI switch modules installed in the computer with counts for all relays on the modules.

Related Links:
How to Chooses the Right Relay
Reed Relay Protection
Switch Maintenance Report Programs

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