Constant value is logged even when logdata is set OFF using Set Tag Attributesd vi

[Uttam Kotdiya]

OS - Windows 2000
Software - Labview DSC runtime 6.1 with patches applied.

Logos 4.4.0.15
Problem :
Constant value is logged even when logdata is set OFF using Set Tag Attributesd vi. I had confirmed that Logdata is Off using Get Tag Attribute vi.
This problem is very random and I am yet not able to find out the exact reason as sometime it works fine and sometime it doesn't. So I an explaining what I am doing. I am continuously reading Energy meter and writing into tags. Also whenever I write to tag I make the logging On(LOGDATA) using Set Tag Attribute Vi. Now I had a option provided to user to stop the logging of all tags SO on a button click I set the logging off of all the tag
s using Set tag attribute vi. When I monitor the logging through Get Tag Attribute it shows logging Off. But after the force wirte time which I had set to 10 minutes it writes constant value even though the Get Tag Attribute vi shows logging Off

I see possible reasons can be
1. Had some parameters need to be set in configuration file of DSC engine
2. Many clients accessing the server.
3. Calling Set Tag Attribute vi many time to set logging on(LOGDATA).

Can anyone guess something from the above description?

[vg]

Hello,

One of the reasons why the Set Attribute and the Get Attribute might be different could be a race condition...tying to read the properties before the change has been written. Have some delay before you read the attribute.

The Historical Trend shows a constant value when it is waiting for a change. As soon as the new logged value comes in, the trend changes correctly. In other words, the Historical Trend will not show the gap of data when the logging has been turned off...it will give you a flat line. But, this will be fixed once the logging is turned on again.

Turning off the logging will keep the system from logging to the database...the Historical trend is the one that might confuse you. You can use the Read Historical Trend. VI and you will see that onc
e the logging has been turned off, no more values are generated on the database...it is only the historical trend indicator the one that is trying to fill the gaps.

Ther NI Hypertrend does not fill the gaps. Maybe this Indicator woull be less confusing for your application.

Just to recap...

Turning the Logging Off with the Set Tag Attribute.VI seems to work fine. What might confuse the user is the behaviour on the Historical Trend.

I hope this answers your question.

VG

[Uttam Kotdiya]

Thanks for your comment.
Well I am able to find out the root cause of problem and had found workaround for that.
When I set the logging off by passing in Set Tag Attribute vi for too many tags say about 4000 tags then it put constant line. Instead of this if I set logging off of about 100 tags at a time. It works fine (i.e. does not put constant value.
But I am not able to understand if that if it is not able to set the logging off properly for large number of tags then how come Get Tag Attribute vi shows the logging OFF for all the tags.