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[KB652]COV limitation

Tags: BACnet

Data acquisition
12 years ago
By BO
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Applies to:

PcVue all versions.
The BACnet implementation from PcVue version 11.2 onwards uses different technology to which this article is not applicable.
Summary:

Sometimes PcVue can no longer subscribe to all COV monitored variables. This behavior may be seen if the host PC has stopped unexpectedly (crash or disconnection).

It may be a limit of the device not specified in its datasheet as the BACnet standard does not specify a property to describe this limitation.

Details:

This behavior can occur if the BACnet network has several BACnet clients and when the PcVue network architecture includes redundancy.

When the active PcVue server is, for example, disconnected from the network the second server subscribes to the same COV variables and a device may reach its subscription limit.

You can check this behavior using wireshark (see attached file). In this case, when PcVue sends a “subscribeCOV” confirmed request, the device returns a standard error. That error indicates there is a resource limitation with the subscribe COV service.

Download attachments: BACnet_COVLimitation_WiresharkSample.png

Created on: 08 Jul 2013 Last update: 13 May 2024