The controller is designed to modulate the AMD-xx-
TD series damper such that it maintains a desired
cfm setpoint . The setpoint is supplied via a 0-10 VDC
analog input (terminals 5 and 6) that is proportional to
that setpoint . The Vari-Green transmitter will output
a 0-10 VDC signal (terminals 3 and 4) proportional to
the actual cfm being measured by the unit . For both
the desired cfm setpoint and the cfm output, a voltage
reading of 10 VDC represents the
maximum
velocity
that was selected at the time the product was ordered .
The selected maximum velocity and the area of the
AMD-xx-TD are listed on a label adjacent to the terminal
block . Example 2 shows how to determine the voltage
corresponding to the desired cfm setpoint .
Example 2:
Determine the voltage setpoint that should be sent to
terminals 5 & 6 to achieve a flow of 4,800 CFM on a 24
in . x 24 in . AMD-xx-TD (area of 4 ft
2
) with a selected
maximum velocity of 2,000 fpm .
Maximum CFM =
4 ft2 * 2,000 fpm = 8,000 cfm
Voltage Setpoint =
10 * (Desired CFM Setpoint /
Maximum CFM)
Voltage Setpoint =
10 *(4,800 / 8,000) = 6 .0 VDC
See example 1 on how to convert the transmitter
voltage output (terminals 3 & 4) to cfm .
AMD-xx-TD Series Damper with a BACnet
Enabled Factory Supplied Controller
Figure 3
shows field wiring for an AMD-xx-TD ordered
with a factory supplied controller configured for BACnet
MS/TP connection .
1 2 3 4 5 6
9
7 8
~
+ -
24VAC
Factory Installed
Terminal Block
Factory
Installed
Jumper
BACnet
MS/TP
AMD-XX-TD w/BACnet
MS/TP Factory
Supplied Controller
Figure 3
This controller is designed to modulate the AMD-xx-
TD series damper such that it maintains a desired
cfm setpoint . The setpoint is established by the
BACnetSetpoint
datapoint . Table 1 lists all of the BACnet
datapoints . The
BACnet Setpoint
is a percentage of the
MaxCFMSetpoint
datapoint, which is set at the factory
based on the maximum velocity which is selected at the
time the unit is ordered .
Example 3:
Determine the BACnet setpoint for a 24
in . x 24 in . AMD with a maximum velocity of 2,000 fpm
and a target flow of 6,000 cfm .
MaxCFMSetpoint =
8,000 cfm (4 ft2 x 2,000 fpm)
BACnet Setpoint =
(Target CFM / Maximum CFM)
BACnet Setpoint =
(6,000 / 8,000) = 75%
With a
BACnet Setpoint
of 75% the actuator/controller
will position the damper to allow 6,000 cfm through it .
Position Control Mode
Example 3 applies when the actuator/controller is
in its factory default operating mode called “Flow
Control Mode” . However, for certain applications it may
be desirable to operate the AMD-TD as a standard
modulating damper . This can be accomplished by
changing the
DamperMode
BACnet data point (see
Table 1
) from
CurrentAirflow
to
DamperPosition
. In
“Position Control Mode” a
BACnet Setpoint
of 75% will
drive the damper 75% open instead of finding a position
that supplies 75% of the maximum airflow .
Safety Override of the BACnet Setpoint
If your application requires the ability to locally close
the damper, the factory installed jumper wire should be
removed and replaced with a normally closed “safety
switch” . When the safety switch is closed the damper
will track the
BACnet Setpoint
as if the jumper wire was
left in place . When the safety switch is open the actuator
will power the damper closed . Interlocking the damper
with a fan such that the damper closes when the fan
shuts down is an example of when the safety switch
feature may be utilized .
5
Air Measuring Dampers: AMD-XX-TD Series
