ADLINK cPCI-7252 - Manual (Page 33)

Operation Theory 23
4 Operation Theory
4.1 Using Relay Output
The PCI-7250 contains two types of relays: Form C and Form A.
Relays R0 - R3 are form C relays, and R4 - R7 are plain form A
type. Note that the cPCI-7252 contains Form C relays only. The
differences between these two types of relays are:
1. Form C Relay: (R0 - R3)
Figure 4-1: Form C Relay
Form C type relays have three contacts: NC (Normal Close), NO
(Normal Open), and COM (Common). The COM post, located at
the middle, must make contact with either the NO post or NC post.
When the control bit is high (1), there is contact between the COM
post and NO post. If the control bit is low (0), there is contact
between the COM post and NC post.
In normal power-up and reset, the relay is in low status.
NO
NC
COM
Control Bit = High (1)
NO
NC
COM
Control Bit = Low (0)