Titus Mixing Box Controls IOM - Manual (Page 8)

Mixing Box Control Installation Manual
IOM-MBC-00 08-30-04
8 of 15
Modulating Control System
Package contents of the modulating (enthalpy) system are
as follows:
Table 8. Modulating (Enthalpy) System Package
Part Code Description Quantity
M7415A Modulating damper motor 1
W7459A Logic module 1
C7400A Solid state enthalpy sensor 1
C7150B Sensor 1
27518 Ball joints 2
27520E 18-inch pushrods 2
Modulating Damper Motor – M7415A
Spring-return, 25-inch/pound damper motor provides
modulating control of economizer systems or ventilation
dampers. Spring returns motor shaft to normal position on
power interruption. Figure 9 depicts a damper motor.
Operation
Tables 9 and 10 provide operating ratings and motor
performance respectively.
A single Damper Motor – M7415 accepts the thermistor
sensor input from the air temperature sensor, mounted in
the discharge or mixed air duct. See Figure 10.
During the occupied period, on a call for cooling, when the
outdoor air temperature is low, the damper motor – M7415
modulates to maintain between 50 and 56° Fahrenheit at
the thermistor.
If the mixed or discharge air temperature is above 56°
Fahrenheit, the damper motor opens to admit additional
outdoor air until the temperature returns to between 50
and 56° Fahrenheit. If the mixed or discharge air
temperature is below 50° Fahrenheit, the damper motor
modulates close, shutting the outdoor air damper until the
temperature returns to between 50 and 56° Fahrenheit.
During the occupied period, the damper will not close past
the minimum position.
If the fully open damper motor cannot satisfy the space
demand, mechanical cooling is sequenced on.
During the unoccupied period, the damper motor overrides
the minimum position setting and drives fully closed. On a
loss of power, the damper spring returns to a fully closed
position.
When in heating operation, outdoor air temperature or
enthalpy conditions are high, economizer operation is
locked out, and the damper motor is held at minimum
position.
Figure 9. Fully Modulating Damper Motor
Table 9. Operation Ratings
Specification Performance
Stroke Fixed 90 degrees, opens counter-
clockwise as viewed from power
end.
Timing 90 seconds
Voltage and
frequency
24 Vac, 50/60 hertz
Maximum operating
torque
25 inch/pound (2.8N-M)
Ambient temperature
rating
-25° to +125° Fahrenheit (-32° to
+52° Celsius) at 25 percent duty
cycle.
Synchronous Normally closed.
Power VA 8
Application Modulating, use with thermistor
mixed-air or discharge sensor
(C7150B)
Shaft Single-ended drive with crank arm
supplied.
Approximate
dimensions
4.5 inches (114 millimeter) high; 5
inches (127 millimeters) wide, and
5.188 inches (132 millimeter)
deep.
Component recognized by Underwriters Laboratories, Inc.