Application

Sequence of Operation

Airflow Control

Siemens Industry, Inc.

Application Note, App 2927

140-1311

2015-07-07

When calibration is in progress, CAL AIR equals YES. After calibration, CAL AIR

returns to NO.

The application uses Autozero Modules connected to AUTOZERO DO8. This means

that the supply and general exhaust flow control devices do not close during calibration

of the transducers.

NOTE:

The LCM does not monitor Fume Hood flow changes for 3 seconds during AVS

calibration.

Airflow Control

Supply flow and general exhaust are controlled by feedback loops that operate control

dampers so that the measured flows maintain their setpoints. The feedback gains SUP

P GAIN and GEX P GAIN are adjustable.

The damper command points (SUP DMPR CMD and GEX DMPR CMD) indicate the

rate at which the dampers move. The points do not indicate damper position. A value

of:

 100% indicates that the damper is being opened as quickly as possible

 10% indicates that the damper is being opened slowly

 0% indicates that the damper does not move at all

 A negative number indicates that the damper is closing at a corresponding rate; for

example, a value of -100% means the damper is closing at full speed

Each damper may be set up for normally open or normally closed operation. To

enhance stable flow control, an advanced algorithm is used to calculate a controllable

setpoint as the value approaches zero cfm (lps).

When the flow is slightly below the setpoint, the LCM sets the damper command to a

small positive number to open the damper gradually. If the flow is far below the

setpoint, the damper command is set to a large positive value to open the damper

quickly. The feedback gains SUP P GAIN and GEX P GAIN are adjusted to tune the

flow loops. The sample loop time for the flow loops is fixed at 0.2 seconds. I and D

Gain are inherent in the system and do not need adjustment.

NOTE:

Set VOL DIF STPT to 0 while tuning the flow loops.

Dampers can be pneumatic or electronic. Pneumatic damper motors receive

pneumatic signals from AO-P modules to accomplish damper motion. The modules

include fill and bleed solenoids that respond to DOs that are pulsed according to

damper command and direction. Electronic actuators extend or retract, corresponding

to the DOs that are pulsed according to damper command and direction.

Floating Control Actuation Auto-correct

In addition to the existing options for floating control actuator full stroke actions, all

floating control actuators are provided with additional logic to fully drive open or closed

when commanded to 100% or 0%.