Siemens SIMATIC S7 Functional Safety Manual

Product overview
1.4 S7-1200 Fail-Safe signal modules (SM)
S7-1200 Functional Safety Manual
Manual, 02/2015, A5E03470344-AA
23
1.4.4
SM 1226 F-DQ 2 x Relay
The SM 1226 F
-DQ 2 x Relay is an S7-1200
signal module (SM) for use in fail
-safe appli-
c
ations. 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 ind
e-
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 interpo
s-
ing relays.
The F
-RLY uses two microcomputers to im-
plement the safety function. Different micr
o-
computers control the two series relay
conta
cts in each circuit. Control of each relay
coil by one microcomputer is verified by the
other microcomputer monitoring the mechan
i-
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.
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.

Siemens SIMATIC S7 Specifications

General

Brand	Siemens
Model	SIMATIC S7
Category	Controller
Language	English