This instruction will perform feedback monitoring.
Check the signal state of the output Q to determine if it is the opposite of the signal state of the feedback input FEEDBACK.
Output Q is set to 1 as soon as input ON = 1. This requires feedback input FEEDBACK = 1 and no feedback errors.
Output Q is set to 0 as soon as input ON = 0 or if a feedback error is detected.
A feedback error ERROR=1 is detected if the opposite signal state of the feedback input FEEDBACK (for output Q) does not follow the signal state of output Q within the maximum tolerance feedback time. Save feedback errors.
If a discrepancy between the feedback input FEEDBACK and output Q is detected following a feedback error, the feedback error is acknowledged according to the parameter assignment of ACK_NEC: • If ACK_NEC = 0, the acknowledgment is automatic. • If ACK_NEC = 1, a rising edge at input ACK must be used to acknowledge the feedback error.
ACK_REQ = 1 The output signals and then indicates that a user acknowledgment is required at input ACK to acknowledge the feedback error. After acknowledgment, the instruction resets ACK_REQ to 0.
To avoid the detection of feedback errors and the need for acknowledgment in the event of passivation of an F-I/O controlled by output Q, the value status of the QBAD signal of the associated F-I/O or the QBAD_O_xx signal of the associated channel/inverted value status must be supplied to input QBAD_FIO .
The procedure for creating and programming a safety program in STEP7 V16 is almost the same as for a standard program. Fail-safe FBs and FCs can be programmed in the F-FBD or F-LAD programming language, and fail-safe DBs can be created in the F-DB programming language. STEP7 Safety Advanced V16 provides some typical fail-safe application blocks that can be used in the safety program. When compiling the safety program, safety checks are automatically performed and additional fail-safe blocks for error detection and fault response are inserted. This will ensure that faults and errors can be detected and trigger appropriate responses to keep the F-system in or into a safe state. In addition to the safety program, standard user programs can also run on the F-CPU.
Open the safety main program block FB1 and call the FDBACK function block in the safety function library on the right
