Premier Control Technologies Flow, pressure, level and temperature solutions
Tuesday, 28th November 2023
Let’s start with the basics, to control pressure we need three components:
Very simple so far!
A PID Controller can be used to control how the valve responds, this is typically set up during manufacturing for optimal use where the valve will open close as fast as possible without over/ undershooting. The desired pressure can be met rapidly in this situation. If a faster response is required the PID can be adjusted, however with a fast climb to a desired pressure there is likely to be an overshoot. This is noticed by the sensor and therefore the PCB will signal the valve to close slightly, this will cause a ripple of over and under desired pressure wave for a short length of time until it is stable, thus optimising without overshooting is the most desirable condition.
Forward pressure controllers are for controlling the pressure after the pressure controller. A supply pressure higher than the desired pressure is given to the pressure controller. The pressure controller will then reduce this in the above way. Recap: the pressure controller will start with a closed valve, the setpoint is entered, the valve will start to open until it meets the equilibrium of the pressure being measured to the setpoint selected. Thus these types of pressure controllers are used for filling applications.
Back pressure controllers are for controlling pressure before the pressure controller. Once again the exact same set of circumstances of use are used. The pressure controller receives the setpoint signal, the sensor measures the pressure, if the pressure is below or at the desired pressure the PCB signals the valve to remain closed. Only when the sensor measures a pressure above the setpoint will it signal the valve to open, releasing the excess pressure back to the setpoint value. Thus these types of pressure controllers are used for pressure relief.
The forward and backward pressure controllers use one valve for this type of control.
Dual valve pressure controllers are essentially a forward and backward pressure controller in one device. They are used for a chambre or other area of closed volume. Closed volume means non flowing. Flow cannot be continuous in a closed chambre, Pressure will flow in to the chambre through the first valve on the pressure controller to fill it until meeting the setpoint pressure. To relieve the chambre the pressure must come out of the same port (as mentioned because it is a closed chambre) here the dual valve pressure controller opens the second valve to let the pressure back out, usually to atmospheric pressure or in vacuum control to a vacuum pump.
Premier Control Technologies offer all three of these types of pressure controller. The Alicat range of pressure controllers are leading with fast response, local displays, large turndown and fast delivery.
Finally there are differential pressure controllers, these controllers keep the pressure between two points controlled. Maintaining the desired pressure difference between these two locations.
These can be in flowing or closed systems as discussed previously. Here's a video of an Alicat dual valve pressure controller:
Alicat pressure controllers are also available with a remote sense port line with the PC3 or PCD3 series. The remote sense port line allows measurement of absolute or gauge pressure at any point in your system and control of flow at a different point so you can maintain pressure exactly where it is needed.
Using a MFM and PC as an alternative to traditional pin gauge testing
Should you have any questions about the principle of pressure controllers or how they can help your application please do get in touch!
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