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Measurement Computing USB-PDISO8 User Manual

Page 18

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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