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TechTime is a Neptronic publication aiming to inform you of common issues highlighted by our technical support team and the best way to deal with them. Each edition features three new topics and will be posted on neptronic.com.

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Time for Change

Understanding COV (Change of Value)

Newly updated Neptronic EFCB & EVCB controllers now support advanced BACnet services (COV Services).

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Native COV service at the controller level helps speed up your MS-TP refresh rate. (DS-COV-B & DS-COVP-B)


Typically, most ASC (Application Specific Controllers) are passive server type devices. Meaning, they respond only when directly and specifically requested. The request occurs when a supervision device or another controller is "polling" the network to read specific data points in order to update their own internal remote database.


For example, "Please tell me your local room temperature and room humidity". The direct result of supervision devices or other controllers that "poll" data points is that you have to wait until the point is actually polled (read) to know if this point’s value has changed or not. On large MS-TP networks of up to 64 devices per MS-TP trunk, this can create a slower response to visualization a device's points and can be problematic for real-time analysis and troubleshooting.


Supporting local BACnet COV services (Change Of Value) greatly increases the speed of a data point refresh since you do not have to wait until the supervision device or other controller "polls" (or reads) the point to update its internal database. By supporting COV, Neptronic controllers can send an update directly to the supervision device or other controller as soon as there is a change of value of any specific data point. The supervision devices or other controllers must be subscribed to the said data points.


To put it simply, it's like a road trip with kids in the car. The kids will "poll" the driver on a regular basis: "Are we there yet". The answer is repeatedly "No". This is inefficient and frustrating. If the road trip supported COV, the kids would remain quiet in the back until driver arrives at the destination and tells them: "Ok, we're here".


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Patrick Lafrance

Technical Support – HVAC Controls

Contact him at this email address patrick.lafrance@neptronic.com