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
2-40 INSTALLATION
Setpoint
Potentiometer
Adjustment
4-20 mA Signal
Setpoint
Source
J1-1,2,3
Baldor Vector/Inverter Drive
Motor
Enc
Available Only
W/Vector
Motor
Output
Motor
Feedback
Process
Feedback
J1-4,5
Third Party
Transducer
Air Pressure Sensor
Output: 4-20 mA
1/4" Hose
Air Pressure
Sense Port
Building Plenum
HVAC Blower
Intake Plenum
MN723H-10/95 11/28/95 1:11 AM Page 52 (Black plate)
Summary of Contents for 23H Series
Page 11: ...1 8 GENERAL INFORMATION MN723H 10 95 11 28 95 1 07 AM Page 12 Black plate...
Page 83: ...3 30 KEYPAD PROGRAMMING AND OPERATION MN723H 10 95 11 28 95 1 13 AM Page 84 Black plate...
Page 99: ...4 16 DIAGNOSTIC INFO AND TROUBLESHOOTING MN723H 10 95 11 28 95 1 14 AM Page 100 Black plate...
Page 125: ...5 26 APPENDIX G MN723H 10 95 11 28 95 1 21 AM Page 126 Black plate...
Page 126: ...MN723H 10 95 11 28 95 1 21 AM Page 127 Black plate...