GUI and Step7 not in sync.

Hi,

pretty fresh to PLC's, but been on a drilling rig last few days with automated machine control and monitoring. Main purpose to assist new personell on machine control, but there have been some bugs making it neccessary to use Step7. The issue im asking about here is not one of the bugs really, but for me it's the one thing I can't figure out.

There were a problem with a parameter that is calculating movement of a wire, times the load on the wire as a measure for the wear on it.

The PLC code was designed to calculate the absolute value of:
("previous position" - "current position") and multiply it with load given in tons and divide the result on 1000, and then iterate like this until the temporary value reaches 0.2 and then add this value to a parameter that keeps on accumulating and reset the temporary back to 0. I don't want to copy the actual code since it's company property. The initial problem was that the value didnt update in the GUI. I found that the temporary value was stuck at some weird looking value (1.!QQ or something like that was the floating-point representation). I went into the db and put the value to 0 and downloaded the db to the plc and that fixed the problem.

The value is updating correctly, so user wise it's no problem no more, but for some reason the value shown in the GUI is not the same as the value I can monitor in the database that the result is being transfered to using Step 7. They keep updating with the same rate, but the value in the database is higher than the one in the GUI. It's also possible to adjust the value in the GUI, but this doesn't cause the values to be in sync.

Anybody know if this is a generic issue in this field and can give me some hints about what might cause this issue? Any help would be highly appreciated!

what is the GUI you are using and what is the sample rate?
It sounds like the GUI sample rate is slower than it should be

The GUI, or HMI program is maybe a better term, is iFIX. I do not think the sample rate is the issue because the values differ with like 500 which is a value it would take days to accumulate by moving wire.

How do you know the iFix is displaying the data you are monitoring in the DB?

(NB A DB in the Siemens plc is a data block)

Concerning your "weird" floating point value, if the 32-bit data contains an invalid floating point number then something wrote that invalid number - you putting it back to zero may fix it but the likelyhood is that it will go wrong again.

L D[AR2 said:

Concerning your "weird" floating point value, if the 32-bit data contains an invalid floating point number then something wrote that invalid number - you putting it back to zero may fix it but the likelyhood is that it will go wrong again.

Click to expand...

Thanks, pretty sure that was the "number". I think your right, but then there is a flaw in the code that I need to take up with the software developers.

The HMI display is clearly not showing the value that I monitor in the data block but if I change the value in the db and download it, it affects the value shown in the HMI display. If I change the value in the HMI display it also affects the value in the db. There is a random difference on about 500 between them, and I can't find anywhere in the code that does the calculation any values being transfered to somewhere else then the db im monitoring.

edit: In the HMI display it's also possible to change hud-settings which gives you an "i" - button next to the parameters which gives you information about addresses on click. Putting the dbxxx.xxxx address given for the parameter into a VAT also gives me the almost 500 higher value then what is shown in the HMI display

Does this mean you are now all OK?

No... Still the same issue with HMI display value and monitored db value not being in sync.

Given that the HMI is not displaying the DB value you are monitoring, but some other DBxxx.xxx value - how do you know what the HMI is supposed to be showing?

L D[AR2 said:

Given that the HMI is not displaying the DB value you are monitoring, but some other DBxxx.xxx value - how do you know what the HMI is supposed to be showing?

Click to expand...

I know because this parameter is part of my bread and butter and it is explained in the source code what parameter is calculated and I fully understand the logic behind the code. The value that I monitor in the DB is increasing with the same rate as the parameter in the HMI. If I could find a value in a DB that is showing the same value as in the HMI I would not be posting this issue here, but I can't find that value anywhere, or any logic behind the value of difference between the one in DB and the one in the HMI display. In the code the calculated value is transfered only to the db that shows the value that is ~500 higher than the one in the HMI display

hi
please tell
- the plc address and format
- the ifix address and format

kalle

olavespedal said:

In the code the calculated value is transfered only to the db that shows the value that is ~500 higher than the one in the HMI display

Click to expand...

What are you using to verify this, visual inspection of the code or the cross reference?

Thanks for answers. I'll come back to your follow-up questions tomorrow