Measurement Computing USB-PDISO8 - Manual (Page 18)

USB-PDISO8 User's Guide Functional Details
Relay contact protection circuit for inductive loads
When you connect an inductive load to a relay, energy stored in the inductive load can induce a large voltage
surge when you switch the relay. This voltage can severely damage the relay contacts. To limit the voltage
surge across the inductive load in a DC circuit, install a kickback diode across the inductive load. Refer to the
contact protection circuit in F . For AC loads, install a metal oxide varistor (MOV). igure 3-10
Figure 3-10. Relay contact protection circuit
C
V
Inductive
Load
Kickback
Diode
NC
+
-
NO
Relay
3-8