Application

Sequence of Operation

Floating Control Actuation Auto-correct

Siemens Industry, Inc.

Application Note, App 6751

140-1331

2015-07-07

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%.

Heating Safety

NOTE:

As a safety feature, these applications include MODHTG FLO to ensure that

adequate airflow is present before heating coils are energized. When the supply

airflow (in fpm as derived from the supply air velocity sensor) is greater than

MODHTG FLO, then the internal point “ok_to_mod” is set to Yes and the modulating

heating device is allowed to modulate.

The default value is 300, which means that the airflow over the heating coil must be at

least 300 fpm.

Since CFM = FPM x Duct Area x Flow Coefficient, the default value of 300 fpm

equates to the following cfms:

In a 12-inch diameter duct and a typical flow coefficient of .7, 300 fpm equates to 158

cfm.

12 inch diameter = .75 sq ft

.75 sq ft * 300 fpm * .7 = 158 cfm

In an 8-inch diameter duct and a typical flow coefficient of .7, 300 fpm equates to 74

cfm.

8 inch diameter = .35 sq ft

.35 sq ft * 300 fpm * .7 = 74 cfm