Sm 1226 F-Dq 2 X Relay - Siemens SIMATIC S7 Functional Safety Manual

1.4.4

SM 1226 F-DQ 2 x Relay

Output channel a.0: Two circuits controlled as one process output channel.
Refer to the isolation description in the SM 1226 F-DQ 2 x Relay (Page 185) Specifications, Digital
outputs table.
S7-1200 Functional Safety Manual
Manual, 02/2015, A5E03470344-AA
1.4 S7-1200 Fail-Safe signal modules (SM)
The SM 1226 F-DQ 2 x Relay is an S7-1200
signal module (SM) for use in fail-safe appli-
cations. The F-RLY has two output channels
(F-DQ a.0 and F-DQ a.1). Each channel in-
cludes two circuits that switch mechanically-
linked contacts at the same time. Each circuit
has two contacts in series controlled by inde-
pendent relay coils.
Each circuit can directly control an actuator in
SIL 3 applications. You can use the two cir-
cuits together to control redundant contactors
or relays for SIL 3 applications with interpos-
ing relays.
The F-RLY uses two microcomputers to im-
plement the safety function. Different micro-
computers control the two series relay
contacts in each circuit. Control of each relay
coil by one microcomputer is verified by the
other microcomputer monitoring the mechani-
cally-linked sense contact.
The series contacts in each circuit are
switched in sequence to avoid common mode
failure by the welding of both contacts.
Product overview
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