As a beginner in the world of BACnet I am looking into clarification on BACnet devices. If I have a system that I want to be compatible with BACnet I am assuming that the system is considered to be an object such as an analog input and that the actual device is a controller or similar that has multiple objects that plug into it. The ASHREA standard 135-2016 states that there is supposed to be exactly one device object type in each device. Is each system on a BACnet(ie HVAC, sensors, lighting, doors, or anything else) considered a device or an object? Thanks for any help!
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A system (such as an air handler), is normally controlled via 1 or more devices. Within each device, each real-world piece of data (such as the measured air temperature, or the control signal sent to a motor) would be a input, an output or a value object.
The control logic for a complex system, like an air handler, would be contained within the collection of devices as either fixed firmware, programmable control modules, or through the configuration of some of the complex standard BACnet object types.
For example, control of a damper within an air handler might be handled by a BACnet Loop object (PID loop) tied to an Analog Output object; detection of adverse conditions with the damper might be monitored by a Event Enrollment object; and a log of the damper's performance might be generated by a Trend Log object. And the overall control logic for the air handler might be handled by a collection of Program objects.
Stepping back and looking at a larger part of the HVAC system, cooperation between the air handler, and the VAV boxes which distribute the conditioned air, might be handled by the Program objects in the air handler devices reading and writing input, output, and value objects in the collection of devices which control the VAV boxes.
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Is each system on a BACnet(ie HVAC, sensors, lighting, doors, or anything else) considered a device or an object?
Anything within a BACnet network with an "instance number" (device address) is considered a DEVICE. Despite the fact that each device must have an internal object (of type 8=device) wich represents itself. In other words, the "device object" is just a way to represent the properties of it's device, but it is NOT the device itself, nor the device is an object.
I hope I have clarified your doubt. Cheers!
gera
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I'll try to narrow the focus a little more to your question; it's kinda slightly incestual in terms of the self-referential (/almost recursive) nature of the model - at least for the one case of a 'device'.
Here's my stab at a simple summary:-
In terms of a explicit/concrete model, BACnet models the essential/high-level pieces (/players or actors within the model) as either an 'object', or a 'property' hanging-off an (/a parent) object (- most likely just one of a related set of properties that happen to belong to the parent object that's referencing it).
Each object belongs to a class/grouping of objects, or rather more correctly, an object-type (- each object is stamped with one of the standard types - in order to identify it's core/base capabilities).
You have physical devices (- "Woo-hoo! I can touch it!!" ;D).
And then you have BACnet's logical rendition of a device - it's (effectively) not a standalone item within the BACnet model - at least not as much/like an 'object' or 'property' is - it's more so only of interest in terms of 'how I get there'/location of the objects treasure chest - to side-step the device & jump straight into showing interest in it's contained 'objects' (- "stuff my wonderful [object] children, what about me [the parent device]!?" ;P); a 'device' in the BACnet world is represented as a specific one of the object-types - a 'DEVICE'-type object (or rather an object whose 'object-type' property is set to 'DEVICE').
So, not only is it more so a gateway to accessing the real items of interest within our OOP (Object Orientated Programming)-like model - the 'objects' & their associated (/child) 'properties'.
But - and here's where it's a little self-referential/egg-&-chicken; it's also represented as an object itself (above & beyond the more typical case if it just been the location where the set of device objects reside upon the BACnet InterNetwork) - that happens to be the keeper of the list of all the objects that relate to that physical device (- at least as portrayed/exposed by the vendor thru the interpretive dance of BACnet & with a slightly vendor proprietary/open rendition of how the values are conveyed), of which, the 'object-list' property of the (logical device/) 'device' object also contains a reference to the 'device' object/itself. =S
If you read this a few times, it should make some sense; and if it does, then it might at first glance seem a little like nonsense/not immediately intuitive (at least not without seeing it in front of your own eyes). ;P
DennisVM-D2i
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