View Full Version : COV - Change of Value using AX JACE
04-09-2009, 08:57 PM
I'm working on a project where several BACnet systems need to poll the value of a point on an AX JACE using COV or change of value. I'd really appreciate any feedback on your thoughts of how this should work. Good or bad comments are welcome. Thanks!
04-10-2009, 05:14 AM
Firstly, not all Bacnet devices support COV. It is becoming more prevalent though.
Basically using COV helps to shorten the poll queue, that is, the number of subscribed points that the controller has to read in its poll sequence. A point that is set on COV will not be called in the poll queue unless the COV flag is set (upon changing over the COV threshold).
With a couple of thousand points the poll time can be 60 - 90 seconds which makes the graphics look slow and crap.
If your devices do not support COV then look at using a Poll on demand folder (I used these in R2 but do not know if they are in AX - haven't used it in a while). This is a separate folder where you can add points. This will exclude them from the poll queue until such time as they are viewed in workbench or else from a graphic.
Hope that helps - I am no Bacnet guru but have made this work for me in the past - I got a 90 sec poll time down to about 18 seconds.
04-11-2009, 05:52 PM
Barry, Thanks for the info. I'm hoping that I can use the COV in order to supply multiple BAS checking the AX JACE for the desired status. The main thing that I am concerned with is making sure that we do not cause too much network traffic. In either case, I should have a couple systems up next week and will let you know what I discuver. It's pretty impressive that you were able to cut down the polling time from 90 to 18 seconds. Thanks again!
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