11/9/2012 3:51 PM | |
Posts: 26 Rating:
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Yes I think there is always some confusion on how point values are passed on the network. If you have a chilled water valve that is 0-100% with a COV limit or 5% and you reference this point directly in the chiller panel (where the point is not located). It will update any time the point changes value by more than 5%. I personally do not think there is a need for the virtual points. You can reference the chilled water valve position directly in the chiller panel. The thing to be aware of if someone sets the chilled water valves COV limit to .1% then yes this will create to much traffic. A.) 1000 MAX($loc1,"AHU1.CHWV","AHU2.CHWV") (PPCL IN CHILLER PANEL) If the above PPCL is in the chiller panel the points will only be updated when they change by their COV limit. This is fine as long as the COV limits are not set to low. B.) PanelA = 1000 sample(10)set("AHU1.CHWV",AHU1.CHWV.VIRT") (PPCL IN AHU1 PANEL) PanelB= 1000 sample(10)set("AHU2.CHWV",AHU2.CHWV.VIRT")(PPCL IN AHU2 PANEL) I assume the chiller panel would then reference the virt points. If so then if the points are changing value quickly for some reason or the COV limit is very low you would limit the amount of changes going to the chiller panel to every 10 seconds. This still might be the best method in case some changes the COV limit of the phyisal chilled water valve or the control of the point starts jumping around alot for some reason. C.)1000 sample(10) MAX($loc1,"AHU1.CHWV","AHU2.CHWV","AHU3.CHWV") (PPCL IN CHILLER PANEL) If the above PPCL is in the chiller panel it will still create the same amount of traffic as the example A. The points will still update based on COV limit so using a sample statement will not reduce the traffic. The sample would possibly only slow down how often the $loc gets updated. Another option to reduce COV traffic is to use Dynamic COVs. I have attached a document that discusses how this option works. AttachmentD:\tmp\download\infolink_automation_fsn_02_08aug.pdf (760 Downloads) |
Last edited by: CS Moderator at: 11/9/2012 4:39 PMreattached document |
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10/29/2013 7:30 PM | |
Posts: 3 Rating:
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This is the most interesting discussion on this topic that I've seen. http://hvac-talk.com/vbb/showthread.php?299252-Siemens-PPCL-Question And I agree, virtual points in this scenario aren't needed. But I almost always take my across-the-ALN-point-value and set a virt equal to it, then use the virtual in the code. I do this so that when the"source" panel fails\goes offline, the code in the "destination" panel doesn't fail and cease to work. The virt will hold the last known value and continue to operate around that value. |
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