Heart beat signal

nyanpasu · Jul 30, 2021

Tom Jenkins said:
I had each slave PLC move the clock time value for seconds into a register in the read data. If the master saw the same value in that register after three data reads it would trip an alarm.

Also the way I do it.

rupej · Jul 30, 2021

daba said:
Definitely not for messaging, the PLCs need to be in RUN or Remote RUN.

I seem to recall being able to successfully send MSG read and MSG write instructions to Rockwell PLCs that are not in run mode. Am I remembering wrong?

dmroeder · Jul 30, 2021

rupej said:
I seem to recall being able to successfully send MSG read and MSG write instructions to Rockwell PLCs that are not in run mode. Am I remembering wrong?

The PLC executing the MSG obviously wouldn't be able to do anything if the PLC was in PGM mode, but the target PLC would respond regardless of what mode it is in. Communications takes place regardless, just no logic executes.

rupej · Jul 30, 2021

dmroeder said:
The PLC executing the MSG obviously wouldn't be able to do anything if the PLC was in PGM mode, but the target PLC would respond regardless of what mode it is in. Communications takes place regardless, just no logic executes.

Thanks, that's what I recalled. Just making sure that distinction is clear for anyone following the thread.

daba · Jul 30, 2021

dmroeder said:
The PLC executing the MSG obviously wouldn't be able to do anything if the PLC was in PGM mode, but the target PLC would respond regardless of what mode it is in. Communications takes place regardless, just no logic executes.

Yes, you can always READ and WRITE to another PLC, regardless of its RUN/PROG mode.

The heart-beat monitoring scenario I posted earlier works for ANY model of PLC, and is the simplest to implement.

JeremyM · Jul 30, 2021

dmroeder said:
The PLC executing the MSG obviously wouldn't be able to do anything if the PLC was in PGM mode, but the target PLC would respond regardless of what mode it is in. Communications takes place regardless, just no logic executes.

This gave me the idea to test whether a controller’s Wallclock object remains active in any mode. If so, then controllers can just read each other’s elapsed milli/micro-second counters. I’ll see if I can conjure an answer from a Logix platform.

dmroeder · Jul 30, 2021

JeremyM said:
This gave me the idea to test whether a controller’s Wallclock object remains active in any mode. If so, then controllers can just read each other’s elapsed milli/micro-second counters. I’ll see if I can conjure an answer from a Logix platform.

I'm fairly certain that if you read a PLC's clock while in PGM mode, the value continues to change. Now if you try to retrieve the result of a GSV reading the clock, it will not change because it requires the GSV to execute to pull it from the controller.

daba · Jul 30, 2021

JeremyM said:
This gave me the idea to test whether a controller’s Wallclock object remains active in any mode. If so, then controllers can just read each other’s elapsed milli/micro-second counters. I’ll see if I can conjure an answer from a Logix platform.

The Wallclock is an OS task that is always active. The problem is that no-one else can read its data.

To date there is no way a third-party can see it - perhaps it will come...

JeremyM · Jul 31, 2021

daba said:
The Wallclock is an OS task that is always active. The problem is that no-one else can read its data.

To date there is no way a third-party can see it - perhaps it will come...

Message the unit’s Wallclock object directly. It’s just a CIP object, after all.

L33er · Jul 31, 2021

The statement "PLC manufacturers don't have an inbuilt health status between networked PLC's in the config options." is not true.

Rockwell have connection status in controllogix platform in Prod/Cons. The older SLC use Message have message.ER bit, which in my opinion is sufficient.
Obviously, you can add additional check logic as needed.

pturmel · Jul 31, 2021

JeremyM said:
Message the unit’s Wallclock object directly. It’s just a CIP object, after all.

Not a documented class number, that I've seen. Would you happen to know? And can share? (Attribute #'s too, please?)

pturmel · Jul 31, 2021

Hmmm. PTP Time Sync object is documented. Not the same as the wall clock object, but much of its info is there.

Tom Jenkins · Aug 1, 2021

If you are going to use a clock for the heartbeat function as I do it is important to have a command in the logic to move it to another register. That way it the register being read will only update if the logic is running.

Aardwizz · Aug 1, 2021

If you are using Rockwell Produce/Consume tags, there's no need for a heartbeat.

Create a UDT for the data you want to transfer. Create as the very first element CONNECTION_STATUS of data type CONNECTION_STATUS, and then the rest the normal data (often DINT arrays and REAL arrays).

The PLCs will automatically handle setting the .RunMode and .ConnectionFailure bits, and the Consuming PLC can take the appropriate action.

JeremyM · Aug 2, 2021

pturmel said:
Not a documented class number, that I've seen. Would you happen to know? And can share? (Attribute #'s too, please?)

Class 0x8B (139)
Instance 1
Attributes 1-12

You'll pick it up quickly: compare local results with GSVs.

Heart beat signal

nyanpasu

Member

rupej

Member

dmroeder

Lifetime Supporting Member

rupej

Member

daba

Lifetime Supporting Member

JeremyM

Lifetime Supporting Member

dmroeder

Lifetime Supporting Member

daba

Lifetime Supporting Member

JeremyM

Lifetime Supporting Member

L33er

Member

pturmel

Member

pturmel

Member

Tom Jenkins

Lifetime Supporting Member

Aardwizz

Member

JeremyM

Lifetime Supporting Member

Similar Topics