Siemens SIMATIC ET 200AL, System Manual

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Product overview
2.3 Fail-safe digital inputs
Digital I/O module F-DI 4+F-DQ 2x24VDC/2A, 4xM12 (6ES7146-5FF00-0BA0)
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Equipment Manual, V1.0, 05/2021, A5E51082342-AA
Figure 2-2 Operator controls and display elements
2.3 Fail-safe digital inputs
The digital inputs of the F-DI 4/F-DQ 2 Fail-Safe module are rated for connection to 24 V DC
sensors/switches and 3/4-wire proximity switches (for example, BEROs: Siemens line of no-
touch sensors) and have an EN 61131-2 type 1 input rating.
The fail-safe module has two 0.5 A sensor supply outputs that can power external sensors
(inputs). All 1oo1 and 1oo2 application modes, except the "1oo2, 2 channel 3-wire
nonequivalent" application mode, use the V
S1
sensor supply to provide power for channels 0
and 1, and the V
S2
sensor supply to provide power for channels 2 and 3. The "1oo2, 2 channel
3-wire nonequivalent" application mode uses the V
S1
sensor supply to provide power for all
four inputs and does not use the V
S2
sensor supply.
Inputs and test circuit
The fail-safe digital inputs consist of four input channels (F-DI x.0 to x.3). You can configure
these channels as four one-out-of-one (1oo1) inputs (SIL 2/Cat. 3/PL d), two one-out-of-two
(1oo2) inputs (SIL 3/Cat. 3 or Cat. 4/PL e), or combinations of 1oo1 and 1oo2 inputs.
Connections Input channel pairs
X10 0 and 2
X12 1 and 3
The fail-safe digital inputs use two microcontrollers to implement the safety function. One
microcontroller monitors inputs 0 and 1, and the other microcontroller monitors inputs 2 and
3. The corresponding channels (0, 2) and (1, 3) form a 1oo2 channel group. The lower
numbered channel of the group is called the primary input and the other channel is called the
secondary input. The first of the two inputs in the channel group conveys the signal in a 1oo2
configuration. For example, if you wire F-DI 0.0 and F-DI 0.2 in a 1oo2 configuration and
configure STEP 7 to use 1oo2 sensor evaluation, the signal state is reported at only the F-DI
0.0 input when you close or open the circuit for both.
When you configure a channel group as 1oo2, the two microcontrollers must sense the same
input change within a configured time. Otherwise, the two microcontrollers detect a
discrepancy error.
You can enable short-circuit testing if you use a sensor supply output to provide power to a
sensor. The short-circuit test checks for shorts to 24 V DC by periodically pulsing the sensor
output off and verifying that the associated input is off.
This short-circuit test also checks for shorts to the other circuit in "1oo2, 2 channel
equivalent" and "1oo2, 2 channel 4-wire nonequivalent" application modes because the test
pulses the two sensor outputs off at different times.
The microcontrollers provide internal test pulses to each other's process input circuits to
verify that sensing electronics are responsive to both "1" and "0" inputs.