Contemporary Control Systems BAScontrol20 User Manual - Manual (Page 40)

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5.2.8 Virtual Points (Channels VT1–VT8)
In the CControls_BASC20_IO kit are eight virtual point components (VT1–VT8) that
are used by a BACnet client to send and receive intermediate data to and from the
BASC20. By intermediate data we mean that the data is neither input data nor output
data but something in between real inputs and real outputs. It could be set-point or reset
data intended for the wire sheet or calculated or status information generated by the wire
sheet. Although BACnet allows for the reading of the BASC20 real input and output
points
— and under certain conditions the writing of real output points — virtual points
have no reading or writing restrictions. Virtual points are treated by BACnet as either a
binary variable (BV) or analog variable (AV) while real points appear as binary inputs
(BI), analog inputs (AI), binary outputs (BO) or analog outputs (AO). The BASC20 logic
engine reads the state of its inputs (AI and BI) and outputs (AO and BO), executes logic,
and then sets outputs (AO and BO) accordingly. In a similar manner, a BACnet client
can “read” the BASC20’s real inputs and will attempt to “write” to the BASC20’s real
outputs. AVs and BVs are a bit different in that they can be configured to be either an
input to the BACnet client (read) or an output from the BACnet client (write). Therefore,
we need to establish rules for the use of AVs and BVs.
If a BACnet client is to read intermediate data from the Sedona wire sheet, this is no
different from accessing data from an input component on the wire sheet. We would call
this “reading from the wire sheet” or Wire Sheet Read. The VT on the wire sheet would
have a channel type (
Chn
Type) of “float out” or “binary out.”
If a BACnet client is to write intermediate data to the Sedona wire sheet, this is no
different from logic on the wire sheet writing to an output component. We would call this
“writing to the wire sheet” or Wire Sheet Write. The VT on the wire sheet would have a
channel type (Chn
Type) of “float in” or “binary in.”
Like universal inputs, virtual points are configured via web pages that are accessible from
the main web page. Click on the title link of a particular virtual point to gain access to its
configuration page. From the Object Type parameter under BACnet Object
Configuration, select either
Analog Variable or Binary Variable
and click the radio button called
Read from Wire Sheet
— if your
intent is for the BACnet client to
read this point. If your intent is for
the BACnet client to write to this
point, click Write to Wire Sheet.
You will notice that the heading of
the virtual points will be either
Wire Sheet Read or Wire Sheet
Write depending on whether the
BACnet client is going to be
reading wire sheet data or writing
wire sheet data.
Upon power loss, all eight virtual
components are retentive up to
seven days. This allows a
BACnet client command to be
retained even if power is lost to
the controller. Backup is accomplished using a super-cap.
Figure 26 — Virtual Configuration Screen