Chapter Three: Overview How The 640B Series Pressure Controller Works
33
How The 640B Series Pressure Controller Works
The 640B Series controller compares the pressure reading to the set point, and positions the valve
to maintain, or achieve, the set point pressure. The controller functions as a PI (Proportional-
Integral) controller. Both the Proportional (P) term, and the Integral (I) term have adjustable dials
on the top of the 640B Series controller.
Example
Assume that your 640B Series controller is positioned for downstream control. The controlled
pressure volume is positioned before the 640B Series controller so the controller will regulate the
amount of gas entering the pressure system.
Figure 13: Sample Pressure Control System
When the actual pressure reading is less than the set point value, the 640B Series controller opens
the valve to increase the amount of gas entering the system. As the valve opens, gas enters the
pressure system, so the pressure rises to meet the set point value.
When the actual pressure reading is greater than the set point value, the 640B Series controller
closes the valve to decrease the amount of gas entering the system. As the valve closes, less gas
enters the pressure system, so the pressure drops to meet the set point value.
Downstream Pressure Control
Gas Flow
Controlled
Volume
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