National Instruments 8-Channel Solid-State Relay (SSR) Digital Output NI 9485 - Manual (Page 10)

NI 9485 Operating Instructions 10 ni.com
When you write an ON command to a channel, the SSR is closed
and the terminal that is connected to the load allows current to flow
or allows voltage to be applied to the load. When you write an OFF
command to a channel, the switch opens, disconnecting the circuit
so no current flows and no voltage is applied to the load.
Protecting Inductive Loads
When inductive loads are connected to the NI 9485 relay outputs,
a large counter-electromotive force may occur at switching time
because of the energy stored in the inductive load. These flyback
voltages can damage the relay outputs and/or the external power
supply.
Limit flyback voltages at your inductive load by installing one of
the following:
• For DC loads—Install a flyback diode within 18 in. of the load.
• For AC loads—Install a metal oxide varistor (MOV) rated for
30 V
rms
or slightly higher.