November 2010 |
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The Protocol Implementation Conformance Statement (PIC)
& BACnet Interoperability Building Blocks (BIBB) |
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The Protocol
Implementation Conformance Statement (PIC) is a written document created by
the BACnet device manufacturer to outline the BACnet features implemented in a
device. The primary purpose of the document is to verify if the device is
compatible to the specified system and has synergy with the client’s
requirements. Therefore, every BACnet
device must have a PIC statement.
From the
document most players in the BAS industry can deduce that the BACnet device can
execute physical input/output, alarming, scheduling, data logging and data
sharing in a RS485 communication medium. This is correct but many assume all
functions relating to the features can be achieved by the device. This
assumption leads to many issues such as overestimation of the devices features
and system integration problems causing increases in costs throughout the
building life cycle. To avoid these
issues we must have a deep understanding of what is included in the PIC statement.
Let's dissect each section of the PIC statement in detail:
Profile: Outlines the specific profile of the BACnet device. BACnet standard specifies various profiles which must support certain features for the device to be classified as the profile. BACnet standard defines the following profiles:
Objects Supported: A
BACnet object is a group of properties which describes a physical or logical
point in a BAS system. The BACnet objects allow logical structuring of the
system without the requirement of proprietary programming. For example Analog Input object type describes
the physical input such as a temperature sensor. A schedule object defines a
logical point of plant schedule. Each object contains mandatory properties
which must be implemented by the vendor if the device supports the object and
optional properties. Do not assume that if a device implements a specific
object that it implements all of its properties. For example if there is a
requirement that a Binary Output change state after a certain amount time, a Binary
Output object which supports the optional properties Minimum_Off_Time and
Minimum_On_Time is required. Similarly the ability to have special exception
scheduling events (e.g. holidays) is an optional property for the Schedule
object.
Data Link and Network Options: It outlines the communication
architecture which the device operates and the networking option available to
view the device in a LAN or WAN.
As it can be
seen from this simple example, choosing the correct device to match the control
requirements is not an easy task. Many take a device which supports BACnet for
granted and assume it can perform many tasks. It is important that the decision
makers have in depth knowledge of the intricacies of BACnet and invest time during the
initial stage of the project to choose the right products to suit the
requirements. The product with the most
features does not imply it is the best product.
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