Baldor 23H series Installation & Operating Manual page 51

MN723H-10/95 11/28/95 1:11 AM
Process Mode Control Example
This example shows an inverter or a vector drive controlling an HVAC process where the control will
try to keep the air pressure in the building plenum at a constant pressure regardless of intake or
exhaust restrictions.
This is a "Feedback" only type of control. The air pressure converts the pressure signal to a 4-20 mA
signal to the control. The control is driving a motor. The motor is direct driving a centrifugal fan.
The "Setpoint Potentiometer Adjustment" is used as the "Setpoint Source". It is used to set the
desired air pressure. The control will then try to adjust the "Process Feedback" from the 4-20 mA
transducer to equal the "Setpoint Source".
The advantage of this system over a damper is the cost savings from operation of the motor at
reduced speeds. In a damper system, the motor is running at full speed with all of the associated
motor losses at 60 hertz. This loss is the "no-load" power that it takes to turn the motor at full
speed. This occurs if the damper is fully closed. The best efficiency is obtained with the damper
fully opened with maximum flow. With a variable speed system, such as the inverter, the motor
losses are reduced with a reduction in motor speed. The best motor efficiency is obtained at all
speeds with the variable speed system.
Figure 2-23 HVAC Process Mode Example
Air Pressure
Sense Port
1/4" Hose
Air Pressure Sensor
Output: 4-20 mA
2-40 INSTALLATION
Page 52 (Black plate)
Building Plenum
Setpoint
Potentiometer
Adjustment
Third Party
Transducer
4-20 mA Signal
HVAC Blower
Baldor Vector/Inverter Drive
Setpoint
Source
J1-1,2,3
Motor
Output
Motor
Process
Feedback
Feedback
J1-4,5
Intake Plenum
Motor
Enc
Available Only
W/Vector