ADLINK PCI-7251 - Manual (Page 42)

34 Operation Theory
2. Form A Relay: (R4 - R7)
Figure 4-2: Form A Relay
Form A relay only has two contacts: NO (Normal Open) and COM
(Common). The COM post can make contact either with the NO
post or not. When the control bit is high (1), the COM post and NO
post are contacted. If the control bit is low (0), the COM post and
NO post does not make contact.
In normal power-up and reset, the relay is in low status.
The relay output contacts are rated at a maximum of 0.5 at
120 VAC (resistive), 1 A 24 VDC, or 0.3 A 60 VDC. You should
reduce these ratings for inductive loads. For more information on
relay contact, please refer to the Appendix.
NO
Control Bit = High(1)
COM
NO
Control Bit = Low(0)
COM