BACnet proxy points and BACnet devices are configured to use COV subscriptions however points are listed as Polled when added to database.

Issue

BACnet proxy points and BACnet devices are configured to use COV subscriptions however points are listed as Polled when added to database.

Product Line

TAC I/A Series

Environment

Niagara G3 all version, ENC-520, ENC-410

Cause

The “Use Cov” property is set to false in the BACnetNetwork Default Tuning Policy.

The "Use Cov" property default is "False". If set to "True", and the assigned proxy points are under a BacnetDevice that supports the Subscribe COV service, any necessary updates (Niagara proxy subscriptions) are attempted using BACnet COV subscriptions to the device. If the subscription attempt succeeds, the “Read Status” property of the point’s BacnetProxyExt displays “COV”. If the subscription attempt for a proxy point fails, normal polling is used and the “Read Status” property shows “Polled”.
 

Resolution

The “Use Cov” property must be set to true for COV subscription to function. It’s a good idea to create a separate tuning policy for BACnet COV subscriptions.

Creating a new Tuning Policy
1. Expand Tuning Policies under the BACnetNetwork
2. Right-clicking an existing policy, then choosing “Duplicate” in the shortcut menu. “Name” it as desired.
3. Open the tuning policy you just created
4. Set “use Cov” to true and save.

Assigning the new tuning policy to the proxy points under the BACnetDevice that is configured for COV subscriptions.
1. Expand the Points folder of the BACnet Device
2. Double-click on the proxy point you wish to configure to use Cov
3. Click on the drop down menu next to Tuning Policy Name and select the tuning policy you created. Save.

Configuring the BACnetDevice to use COV
1. Open the BACnetDevice under the BACnetNetwork
2. Set the “Use Cov” property to True.

Note: Typically, you create multiple tuning policies in the BACnetNetwork—especially if you have multiple BACnet network ports enabled. This allows you to reference different tuning policies from BACnet proxy points under different networks (often with vastly different performance capabilities). For example, points under a BACnet MSTP network would likely use different tuning policies than those under a BACnet IP network.

Reference the “About BACnet Tuning Policies” section of the Niagara AX-3.x BACnet Guide document for additional information.