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Fume Hood Controller Owner's Manual 
12 
 
Siemens Building Technologies, Inc. 
Basic Operation 
The Fume Hood Controller provides Direct Digital Control (DDC) technology for controlling 
fume hood face velocities in a manifolded fume hood exhaust system. 
High and Low Exhaust Flow Control 
The Fume Hood Controller can operate at two different setpoints, described as HI flow and 
LOW flow setpoints. The low setpoint can be set to zero to send the controller into an OFF 
mode. The OFF mode shuts off the flow alarms and closes the exhaust flow control device 
and allows the controller to go into a standby mode of operation. 
The Operators Display Panel (ODP) can display HI/LOW setpoint or output exhaust flow in 
CFM. Due to display limits, the actual number displayed is CFM divided by 10. 
Control Loops 
The PID loop controls the exhaust flow control device based on the values of the exhaust 
flow and the flow setpoint. The loop output controls the supply and exhaust through a time 
modulation scheme. The control loopout ranges from -100 to 100%. 
•  -100% is the maximum supply that closes the exhaust flow control device at full 
speed. 
•  0% holds the exhaust flow control device at its current position. 
•  100% is the maximum exhaust that opens the exhaust flow control device at full 
speed. 
 
Electronic 
The controller sends a separate signal to each of the two inputs that reside on the AO-E 
module. For values of 100% to 0%, the controller sends a decreasing percentage of the full 
signal length to the retract input. For values of 0% to -100%, the controller sends an 
increasing percentage of the full signal to the extend input. 
Pneumatic  
The controller sends a separate signal to each of the two solenoids that reside on the AO–P 
module. For values of 100% to 0%, the controller sends a decreasing percentage of the full 
signal length to the exhaust solenoid. For values of 0% to -100%, the controller sends an 
increasing percentage of the full signal length to the supply solenoid. 
Calibration 
Air Velocity Sensor - Calibration of the controller's air velocity sensor is periodically required 
to maintain accurate air velocity readings.