Siemens PLC Fault Safety Function - FDBACK Function Block Case Download

1 Problem Description：

When it is necessary to control the motor through a safety circuit, AC contactors and safety output modules are usually used to achieve control, and feedback monitoring is used to ensure safety. In this case, the safety PLC will monitor the condition of the AC contactor in order to timely detect internal faults, especially problems such as poor contact of contacts, and take corresponding measures to ensure that normal operation does not affect the realization of safety functions. If the power contactor is detected to be in an unsafe state, such as poor contact or wiring issues, the system will issue an error signal and activate safety functions to prevent any potential safety risks.

2 Instruction Introduction：

This command will perform feedback monitoring.

Determine whether the signal state of output Q is opposite to that of feedback input FEEDBACK by checking its signal state.

After inputting ON=1, output Q will immediately be set to 1. This requires feedback input FEEDBACK=1 and no feedback errors.

As long as input ON=0 or if a feedback error is detected, output Q will be immediately set to 0.

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, a feedback error ERROR=1 will be detected. Save feedback error.

If a difference is detected between the feedback input FEEDBACK and output Q after a feedback error occurs, the ACK_ NEC parameter allocation confirmation feedback error: • If ACK_ If NEC=0, confirmation will be automatically performed If ACK_ If NEC=1, the rising edge at the input ACK must be used to confirm the feedback error.

ACK_ REQ=1 outputs a signal and then indicates that a user confirmation is required at the input ACK to confirm the feedback error. After confirmation, this command will ACK_ Reset REQ to 0.

When the F-I/O controlled by output Q undergoes passivation, to avoid detecting feedback errors and avoiding the need for confirmation, input QBAD must be used_ FIO provides QBAD signals for related F-I/O or QBAD signals for related channels_ O_ Xx signal/inverted value state.

The process of creating and writing security programs in STEP7 V16 is almost identical to standard programs. You can use F-FBD or F-LAD programming languages to write fail safe FB and FC programs, and use F-DB programming language to create fail safe DBs. STEP7 Safety Advanced V16 provides some typical fail safe application blocks that can be used in security programs. When compiling a security program, it will automatically perform security checks and insert other fault safe blocks for error detection and fault response. This will ensure that faults and errors can be detected and trigger appropriate responses to keep the F system in a safe state or enter a safe state. In addition to security programs, standard user programs can also be run on F-CPU.

3 Usage：

When FEEDBACK=1, after input ON=1, output Q will immediately be set to 1. At FDB_ If FEEDBACK=0 within the time set by TIME, the output Q remains at 1.

When FEEDBACK=1, after input ON=1, output Q will immediately be set to 1. At FDB_ Within the time set by TIME, if FEEDBACK=1, the output Q remains at 0. And request fault confirmation.

4. Extended Thinking:

FDBACK function block can only be called in PLC with F. If we want to use it in conventional PLC, can we write a feedback program.

Program segment 1 is the condition for output.

Program segment 2 is the detection of feedback time.

Program segment 3 is the fault setting after exceeding the feedback time, which needs to be manually confirmed, otherwise it cannot be output again.

Program segment 4 is for resetting faults.