Siemens SIMATIC ET 200AL, System Manual

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Product overview
2.4 Fail-safe digital outputs
Digital I/O module F-DI 4+F-DQ 2x24VDC/2A, 4xM12 (6ES7146-5FF00-0BA0)
Equipment Manual, V1.0, 05/2021, A5E51082342-AA
15
See also
Accessories for the ET200AL distributed I/O system
( https://support.industry.siemens.com/cs/us/en/view/89254965 )
2.4 Fail-safe digital outputs
The digital outputs of the F-DI 4/F-DQ 2 Fail-Safe module are for use in fail-safe applications
and are suitable for various actuators such as the following:
•
Solenoid valves
• DC contactors
• Indicator lights
The two digital outputs each have P- and M-switches that are rated to connect 24 V DC
actuators with up to a 2.0 A rating. The two digital outputs use the load voltage 2L+ with a
maximum current of 4.0 A. This means that the total current usage by the two digital outputs
cannot exceed 3.96 A because the 2L+ supply uses about 40 mA.
Outputs
The fail-safe digital outputs consist of two output channels (F-DQ x.0 to x.1). You can use
each output for SIL 3 applications.
Connections Output channel
X14 0
X16 1
Each output consists of two switches:
•
A P-switch connects 24 V DC positive (L+) to the load.
• An M-switch connects the load to M or 24 V DC return.
Both switches must be ON for current to flow to the load.
The fail-safe digital outputs use two microcontrollers to implement the safety function. One
microcontroller controls the P-switch while the other microcontroller controls the M-switch.
Status of the P-switch is fed back to the other microcontroller (the one that controls the
M-switch). Likewise, status of the M-switch is fed back to the other microcontroller (the one
that controls the P-switch). The microcontrollers use the feedback to verify that the output
switches are operating properly and in the commanded state.
You must configure a "Maximum readback time" that specifies the allowed delay for the
output voltage to respond to the switch change.
The fail-safe digital outputs regularly test each P- and M-switch to verify that each switch is
still functional and under independent control. Your configured "Maximum readback time"
also sets the duration of the "OFF" test pulse. You must configure a "Maximum readback time
switch on test" which sets the duration of the "ON" test pulse. Choose these durations short
enough to not affect your load.