Improving Relay Life for PXI-2567

Monitoring Relay Usage

• Use the niSwitch Get Relay Count VI or the niSwitch_GetRelayCount function to track relay usage. You can then analyze the relay counts on your PXI-2567 to better manage the use of each relay.
• Edit test sequences to reduce the number of switching cycles.

Preventing High Currents from Damaging Relays

High inrush current can damage relays when switching with capacitive loads. This is because the inrush current needed to charge the capacitive load may be substantially higher than the steady-state current through the system. To mitigate damage from high currents, consider the following approaches:

• Use series resistance when switching with capacitive loads to prevent high inrush currents from damaging relays. Examples of capacitive loads include: DMMs, long cabling, and DUTs.
• Turn off power supplies or other voltage sources connected to the relay before switching to ensure that voltage levels are the same on both sides of the relay.

Limiting Flyback Voltages

Flyback voltages are large counter electromotive forces that occur when relays that are connected to inductive loads open. This counter electromotive force generates large voltage spikes across your relay contact because of the reactive energy stored in the load. The flyback voltages can severely damage the relay contacts and greatly shorten the relay life. To limit flyback voltages at your inductive load, consider either of the following options:

• Install a metal oxide varistor (MOV) for AC loads as shown in the following figure.

  
  

  

  
  

• Install a flyback diode for AC loads as shown in the following figure.