WinCC Flex 2008 ADV Trend View Switch Buffer

Does anyone have any experience with these.
I'm trying to set this up and having issues with it.
I am trying to a trend to monitor inputs but they cycle to fast so I am attempting setting up a buffer so I don't miss data.

I am wondering if I need to setup an array and cycle thru it my self or how this bit buffer option works. The help file is very vague.

You need a buffer bit trend. I bugged Siemens about it enough a few years ago they made a how to for setting them up. I will find a link.


http://support.automation.siemens.com/US/view/en/21913875

Thanks alot. I will give that a try. Siemens sent me a demo HMI program with no information on how to use it. It looked like it was imported from 2005 and no longer worked.

I have tired using this as an example and I have had no success.

I am trying to monitor a M bit triggered by a 5 hz timer. I would expect the trend to be consistant, but it seems to miss often.

When I try setting up the bit buffer it doesn't seem to work at all. Has anyone done this before?

End result, I would like to be able to monitor a prox or switch for pulsing/flickering?

Thanks for any advice,
-Joel

Yes, I use it and it is easy.

You dont write it, but you do know that you have to create the buffer in the PLC yourself, with PLC code ? I think not, because the trend view in WinCC Flex cannot "miss" logging values. The trend view just displays the content of the buffer, and it is your own code that must do the logging by writing to the buffer.
The difference with the "switch" version is that it means you can display one buffer on the screen while another is being created. Do you need this ? I guess you should start with the non-switching variant first.
The only thing I fought with was to set the right Trend Transfer bit. Since it is a word, you can try to write a "-1" to it, which is the same as setting all the bits in the word.

edit: Oh yeah, one must set at least 2 of the bits in the TrendTransfer tag. The "trend Group" bit (bit 15), and the bit for the buffer in question. Like I said before, if you only have 1 buffer trend view, just write a "-1" to the TrendTransfer tag.

So if I wanted to constantly monitor an input for example.
Create 2 arrays of lets say 100 ints.
Every scan increment a counter and store the state of the sensor.
When it's full read the buffer and log to the other buffer.
And switch back and forth.

Or do you think I will not need the "Switch buffer"

Thats what I do

I have an array of 500. I have a timer that logs the data into the array then index to the next. I do the index in SCL because it makes it so easy to work with arrays. I also have a timer in the plc that resets the trigger. This is set at 500ms and makes the trend appear on the screen as the machine is running. At the start of another cycle I use the block fill to 0 the array.

You can only decide yourself if you need the switch buffer.
Without the switch buffer, and if you dont halt the logging to the buffer, the trend will display old and new values together.

With the switch buffer you can achieve that the trend updates automatically each time the buffer is full.
If you scan time is 10ms, and there are 900 points on the trend (I think that is the max), the trend will update (switch over) every 9 seconds.

I think you would need to have a switch that changes between "hold" and "update" of the display. This so that if something intersting is displayed on the curve it isnt immediately lost again.

In my experience it works quite well with ethernet.
There is a hard limit of how many bytes can be transferred at a time (240 bytes I think). You can see on the trend how the display updates the curve in steps as another chunk of 240 bytes are recieved. For an array tag set to update every second, and with a large trend buffer, it takes several seconds to display the full curve. I think that with MPI or DP, you can forget a "live update" of the curve.

To start off I will go with the option of 2 arrays of 500 and displaying when they are full. See what kind of timing issues with writing one buffer while displaying the other. This system is currently using ethernet so that should help. Thanks for the info.

I don't know if I will be able to accomplish what I want to do.

When I press the my "show trend" button the HMI takes about 4 seconds to display a trend of 500 points.

So even with a switch buffer of 500ms each.
It seems like I would fill 1, display it while filling another. While displaying the data I would end up missing some data.

Do I have to find a "sweet spot" where I can fill both buffers in the amount of time it takes to display?

Charles do you have an example of your setup? I don't see how your getting passed the displaying delay time issue. Or maybe it just isn't an issue on your system.

Is it a PN CPU or are you online via a CP343-1 ?
Are you trend values integers or reals ?

CP343-1
Integers (would just be bools but that isn't an option that I can see)

I running WinAC RTX with WinCC Flexible Runtime. I get fast updates.

CP343-1. Quite slow I am afraid.

WinAC RTX, with Flex RT. Both running on the same PC I guess. Very fast.

I gave up on the switch buffer.
The timing issues with my HMI / PLC didn't work out for me.

So I took the cheaters way out.
I just monitor the I/O/M and use a positve edge to trigger a counter and the trend shows the current counter status.

Not what I was going for but it works.