Problems with fractional alarm levels

[mihonyc]

Hi

We use LV8.6 with DSC module under XP Pro.

I am building an application which should configure/monitor alarms on locally deployed numeric double shared variables.

I don't seem to be able to set fractional alarm levels neither through Project Explorer nor through Distributed System Manager. E.g. I try to set level of HI_HI alarm to 1.50. What I see is that the values does change when I enter it, but it gets rounded up to the closest integer if I open Properties for this shared variable once again (or use property node to read it).

If I use property node to set the levels I am able to get them set to fractional values. There is an issue with auto-acknowledgement of the alarm in the this case though (the alarm does not get auto-acknowledged when the variable's value gets back to non-alarm range).

I would appreciate any comments on the issues I'm experiencing.

Thank you in advance!

[jareds]

Lockia,

It looks like there may have been a problem with this in LabVIEW 8.6.  I've found that it works fine in LabVIEW 8.6.1 and 2009.

Have you been able to get other alarms to auto-acknowledge?  Or have you only tried with the fractional ones? 

[mihonyc]

Jared,

thank you very much for reply and please excuse me for the delayed response.

I've upgraded to LV 8.6.1. and this solved the problem partially. Now I am able to set fractional alarm levels (both programmatically and through Project Explorer/Distributed System Manager). I am still having a problem with auto-acknowledgement of alarms with fractional levels.

To reproduce the issue you may want to do the following.

In Distributed System Manager enable e.g. HI_HI alarm of some double shared variable and set a fractinal level for this alarm. Now if you set the value of the variable above the alarm level you'll see that the variable goes into alarm state. If then you set a new value of variable below the alarm level the alarm will not auto-acknowledge and the variable will still be in alarm. (The situation is pretty much the same if I all this happens "programmatically " when my application is running).

If you perform all the same steps with an integer alarm level or for the boolean shared variable you'll see that after changing the variable back to non-alarm value the alarm clears.

Now I'm pretty sure that this is an internal bug within the LV and it does not have much to do with my code.

I'd appreciate it very much if some of NI engineers confirmed it.

Have a nice day!

[jareds · Accepted solution]

How far below the alarm level have you tried going?  In LabVIEW 2009 at least, there's a deadband that can be set for each alarm.  By default the deadband is 1, which means that you need to move at least one point below the alarm to cause it to auto-acknowledge.  Here's a good help file which explains how exactly this works.  In short, if you want to auto-acknowledge when the value drops exactly below the alarm level, then you need a deadband of 0.  I hope this helps. 

[mihonyc]

Jared,

thank you for your comment.

You were right, the alarms did not auto-acknowledge because of the deadbend setting. I guess I was confused because the deadbend happens to be set not in relative units (%) but in absolute units. E.g. if HI_HI alarm levlel is 5.50 and you want the alarm to auto-acknoledge at 5.49 you need to set the deadbend to 0.01.

Have a nice day!