Table of Contents
Advertisement
13.2 Metasys N2
•
The gateway acts as a Johnson Controls Metasys N2 slave, and supports
N2 analog input, analog output, binary input and binary output object types.
•
Analog input (AI) objects are used for monitoring analog status items. AI
objects support low alarm limits, low warning limits, high warning limits,
high alarm limits and differential values. Change of state (COS), alarm and
warning functions can also be enabled. An AI object will accept an
override command, but will not change its actual value or indicate override
active. A "multiplier value" is associated with the object, and is multiplied
to the point's value to produce the floating-point AI value sent to the NCU
(AI value = [point data value] X multiplier).
•
Analog output (AO) objects are used for setting and monitoring analog
control and configuration items. An AO value can be modified by issuing
an override command. Issuing a release command will not cause the AO
to automatically return to its pre-override value, nor will the AO
automatically return to its pre-override value after a certain time period of
no communication. A "multiplier value" is associated with the object, and
the floating-point AO value is divided by this multiplier to produce the result
that is passed on to a point's value (point data value = [AO value] /
multiplier).
•
Binary input (BI) objects are used for monitoring discrete (digital) status
items. BI objects support COS, alarm enabling and normal/alarm status
indications. A BI object will accept an override command, but will not
change its actual value or indicate override active. A "bit mask" is
associated with the object, and is used to determine the current state of the
BI by inspecting the point's data at the bit location(s) indicated in the bit
mask. If all of the bit locations of the point's data value indicated by a "1" in
the bit mask are set, then the BI's current state is set to "1". Else, it is set
to "0". The point data's least-significant bit (LSB) is bit #0, and the most-
significant bit (MSB) is bit #15.
•
Binary output (BO) points are used for setting and monitoring discrete
control and configuration items. A BO value can be modified by issuing an
override command. Issuing a release command will not cause the BO to
automatically return to its pre-override value, nor will the BO return to its
pre-override value after a certain time period of no communication. A "bit
mask" is associated with the object, and is used to determine the current
state of the BO by modifying the point's data at the bit location(s) indicated
in the bit mask. When the BO's current state is set to "1" by the NCU, then
the bit(s) of the point's data indicated by a "1" in the bit mask are set.
Similarly, when the BO's current state is set to "0" by the NCU, then the
bit(s) of the point's data indicated by a "1" in the bit mask are cleared. The
point data's least-significant bit (LSB) is bit #0, and the most-significant bit
(MSB) is bit #15.
48
Advertisement
Table of Contents
