Programming Logic Operations; Programming Mode-Dependent Safety Functions - Siemens SIMATIC S7-1200 Safety Programming Manualline

3 Methods for Safety Programming
3.6

Programming logic operations

Tasks of the blocks

Generate release signals to control the safety-related actuators based on the
relevant safety functions

Link the sensor enables, operating mode enables, etc. to the control signals of
the actuators
Recommendation

Use mainly AND and OR logic elements

Reduce the use of SR blocks to a minimum

Avoid jumps in binary logic
3.7

Programming mode-dependent safety functions

Recommendation
Divide the logic into different levels (see IEC 62061):

Level 1: All safety functions that are independent of modes and plant statuses.
–
Logic ANDing of all safety functions that are always active.
–
These are typically emergency stop facilities.

Level 2: All mode-dependent safety functions.
–
Logic ORing of safety functions that are only active in certain modes.
–
For example, safety doors in automatic mode, alternating with enabling
buttons in service mode.
Example
Three safety functions are implemented on a machine: The "estop" emergency
stop function is active in each mode. The "guardDoor" safety door monitoring and
the "enablingSwitch" enabling function are only active in one mode.
Figure 3-8: Programming modes
Safety Programming Guideline
Entry ID: 109750255, V1.0, 10/2017
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