18
2 H) AI4 CO2 / Other Sensor Input Operation
AI4 CO
2
Sensor Input Operation
The VT76XXE controller features a 0-10VDC input (AI4) that is used for monitoring using any 0-10VDC
sensor or to control the building CO
2
level.
Using any 0-10VDC value for monitoring
If the AI4 input is used for monitoring purposes only (even if monitoring CO
2
with a CO
2
sensor), the AI4
parameter should be set to
None
(not CO
2
).
The value of the AI4 input can then be monitored at the network level (BACnet™ front end) under:
-
AI4 value BACnet™ object (in VDC)
Locally at the controller, the value of AI4 can only be obtained by measuring the voltage between Scom
and AI4 using a voltmeter. The value of AI4, if AI4 parameter is set to
None
, will not be displayed on the
controller’s screen at any time.
Using a 0-10VDC CO
2
sensor for control purposes
If the AI4 input is used with a CO
2
sensor for control purposes, the AI4 parameter should be then set to
CO
2
. In this case, a CO
2
value will be displayed at the end of the configuration parameters list showing the
CO
2
level measured by the sensor in ppm (particles per minute).
The value of the AI4 input will also be displayed at the network level under:
-
Room
CO
2
Value BACnet™ object (in ppm)
-
AI4 value BACnet™ object (in VDC)
When AI4 parameter is configured to CO
2
,
the CO
2
control is enabled only in Occupied mode
. The
VT76XXE will use these CO
2
values to determine the building’s CO
2
Level for the IAQ control sequence.
The following example shows the value of the BACnet™ objects as well as the values at the local
controllers based on the AI4 parameter setting and Occupancy status. The example uses a 0 – 2000ppm
CO
2
sensor with a signal of 0-10VDC.
AI4
parameter
Occupancy Sensor Voltage
CO2 display at
local controller
Room CO2
Value
Transferred
CO2 value
None Occupied
5.0VDC No 0ppm
0ppm
CO2 Occupied
5.0VDC Yes 1000ppm
1000ppm
None Unoccupied
5.0VDC No 0ppm
0ppm
CO2 Unoccupied
5.0VDC Yes 1000ppm
0ppm
