S7-1500 turn on SF LED intentionally

[grnick50]

Hello all,

I was wondering if there is a way to turn on the SF LED using an instruction in the program.

i.e. My PLC has no HMI and it has modbus TCP comms. I want when the communication is lost to turn the SF LED on.

I used Gen_usrMSG & Program_Alarm instructions to write a message in the Diag buffer but it does not turn the SF LED on.

Regards

 

[mk42]

I'm really curious if there's an answer to this. I've spent a lot of my career trying to get red LEDs to turn off on Siemens processors; I've never tried to turn one on before.

 

[boneless]

I guess you could call an FC that you didn't download? Or do an invalid BCD conversion?

This reeks of bad practice... I think adding a light would be more appropriate..

 

[grnick50]

What I did to get the LED on is to intentionally write to a non existent PQW.
I do this after I generate a user message in the diagnostic buffer which says "Ignore Q 224 Error" this is a Modbus FLT.

It works.

 

[mk42]

What I did to get the LED on is to intentionally write to a non existent PQW.
I do this after I generate a user message in the diagnostic buffer which says "Ignore Q 224 Error" this is a Modbus FLT.

It works.

I have to back up boneless, this sort of solution sounds like the exact opposite of a "best practice". Do you have no free outputs to hook up an LED on the panel?

 

[grnick50]

Personally I would never do that. As you say I could use a Lamp or a basic HMI to do the alarming.

The question was raised in a training class I was teaching for TIA portal.
The student asked if he could light the SF LED if a Modbus station is lost, in the same manner as when a Profibus station is lost.

Personally I would not follow that practie but I have to answer the question, of course noting that I dont agree with that.

regards

 

[Bratt]

You can write custom messages to the diagnostic buffer that will be displayed if you have a 1500 with the small screen on the cpu.

 

[dwoodlock]

can you not just display an alarm for a communications fault on the display panel??

https://support.industry.siemens.co...500-display-and-web/91821/?page=0&pageSize=10

If you look at that thread you can find some direction about how to do it.

As others are saying, using the SF for not an SF, just doesn't sound like the best route.

 

[Lare]

SFC51?

http://www.plctalk.net/qanda/showthread.php?p=654255

 

[L D[AR2P#0.0]]

I thought this was leading to using the SF LED to flash out a message in morse code and then using a mobile phone to display it....

 

[ASF]

"we don't want to spend the money on a fault lamp, because the PLC already has a red light on it! Just use that one and we'll cut a hole in the panel door so the operators can see it!"

But seriously, I'm impressed, not only that you found a way to do it, but also for your commitment to answering a student's question accurately

 

[grnick50]

I believe that when you train someone, you have the obligation to answer as much as possible. It is not my buisness why the student needs to know that and how he/she will use it.

As I said although I disagree I had to answer.
The question came up when we were going through the diagnostics instructions of the 1500 and specifically the LED instruction that reads the LED status.
So for some student it was natural to think "If I can read the LED, why cant I write it status"?
You will be amazed of what you are being asked in a training, but regardless the trainer needs to answer since at the end of the day he is being assesed by the students.

Regards

 

[ASF]

I wish half of my trainers back in the day thought that way. The response I usually encountered was a blank look, half an hour trying to work out the problem doing things I'd already tried, and then when they were clearly no closer to finding a solution but were all out of ideas, the classic "no, I want you to figure it out yourself, it's a test".

Which in some ways wasn't the worst thing, because it taught me perseverance and to find a way to find things out on my own, but still