Chapter Three: Overview How The 640 Series Pressure Controller Works
35
How The 640 Series Pressure Controller Works
The 640 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 640 Series controller.
Example
Assume that your 640 Series controller is positioned for downstream control. The controlled
pressure volume is positioned
before
the 640 Series controller so the controller will regulate the
amount of gas entering the pressure system.
Downstream Pressure Control
Gas Flow
Controlled
Volume
Figure 14: Sample Pressure Control System
When the actual pressure reading is
less than
the set point value, the 640 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 640 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.
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