Safety PLCs have great monitoring and diagnosis capabilities, which allow them to maintain the health of the safety function even if internal failures occurred. A safety PLC will detect the internal failure of any safety module connected to the safety control circuit.
One of the crucial aspects of any safety circuit is the acknowledgment step before allowing your process to run again. Safety standards dictate the need for acknowledging the safety condition before starting the process again.
This ensures that running the machine was enabled after an operator recognized the risk condition, cleared the risk, and acknowledged the safe operation once again.
In this article we will talk about one useful safety PLC instruction in TIA Portal; this is the ACK_GL or Global acknowledgment function.
Contents:
The acknowledgment step is one of the most important aspects of any safety control circuit, it simply means that if there is any risk condition that has occurred and stopped your machine, the machine can’t run again until an acknowledge signal is provided, even if the risk condition is cleared.
We saw in previous articles explaining different common safety functions like the ESTOP or the SFDOOR instructions, there was always an ACK signal that needs to be provided before the output can be ON again, even if the risk is cleared.
This is to ensure that whoever will acknowledge the safety condition will ensure that the machine can now safely start working again. See picture 1.
That was for the safety instructions, but what about the safety modules?
As you know, safety PLCs and their safety modules are designed, tested, and certified to comply with safety standards, which include diagnosis, monitoring, and redundancy of input and output signals and Self-diagnosis of internal software and hardware failures.
That means, when an internal failure in one of the safety modules occurs, the safety PLCs will detect that failure and the safety module will go into what is called passivation. Which means your process will probably stop.
And after you clear this fault, you will have to acknowledge the safety condition again before the system can run. The acknowledgment step of the safety input/output modules or F-I/O is known as reintegration.
When passivation occurs in an F-I/O with inputs, the safety PLC will provide the safety program with fail-safe values instead of the process data pending at the fail-safe inputs in the PII.
When passivation occurs in an F-I/O with outputs, the F-system transfers fail-safe values to the fail-safe outputs instead of the output values in the PIQ provided by the safety program.
After you clear this fault, you will have to perform acknowledgment or reintegration of the F-I/O again before the system can run.
A passivation to an F-I/O will occur if any of the following cases are present:
Reintegration for an F-I/O module with inputs, the process data pending at the inputs in the PII are provided again for the safety program.
For an F-I/O with outputs, the F-system again transfers the output values provided in the PIQ in the safety program to the fail‑safe outputs.
This can be done automatically or following user acknowledgment in the F-I/O DB depending on the hardware configuration of the module, but the safety standards insist on making it with an acknowledgment.
as we mentioned before, any safety module whether it is a safety input module or a safety output module will have built-in self-monitoring and diagnoses functions, these functions run in the background, to ensure the safe operation of your module.
An F-I/O DB is the built-in dedicated data block that is used by the safety PLC to store related data of the safety module. See picture 2.
As you can see from picture 2, each safety module has a lot of internal parameters and configurations related to the monitoring and redundancy of the module, and each safety module will have a data block or a DB. To store these data inside. See picture 3.
As you can see from picture 3, the DB of the safety input module, has a lot of parameters inside, these parameters provide all data related to the safety module.
For example, if one of the safety input modules F-DI was taken out of the power rail, the safety PLC will pick up this fault and stop the process until the safety input module is put back into its place, but even then the process will not start until you acknowledge the F-DI for reintegration as we mentioned before.
If an F-I/O fault is detected by the F-I/O, the passivation of the relevant F-I/O will occur. Once the F-I/O fault or channel fault has been eliminated, reintegration of the relevant F-I/O should be done. You can assign a reintegration by user acknowledgment either two way.
As we said before, we can use the ACK_REI bit of the related safety module to separately reintegrate this module when it is passivated.
If passivation has occurred, you will need to a rising edge trigger with the ACK_REI bit after you clear the module fault. See picture 4.
The ACK_GL or Global acknowledgment instruction creates an acknowledgment for the simultaneous reintegration of all F-I/O or channels of the F-I/O of an F-runtime group after communication errors, F-I/O errors, or channel faults. So you wouldn’t have to separately reintegrate each module. See picture 5.
Download the Safety PLC logic in PDF and the source code in the TIA portal.
P.S. password for the safety PLC code is 123
Safety PLCs provide many safety functions that are built in to ensure the safe operation of your process while considering all safety issues employed by the standards.
You can program all these safety functions using a normal PLC, but your code will be so large that you might miss some details, also, a normal PLC will not provide the internal monitoring and diagnoses that the Safety PLC provides.
Of these safety functions, there is global acknowledgment. It is very simple to use, but very important and critical for the safety of your process. And it mainly depends on the great monitoring and diagnosis capabilities of the safety PLCs.
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