Closed Loop Electronic Pressure Controller

Electronic pressure controller provides closed loop PID
control of outlet pressure.
Image courtesy of Rotork Instruments - Fairchild

The control of pressure in a line, tank or other vessel is a common operation found in the process control field. Many pressure regulators are fully mechanical, with counterforce mechanisms used to set an equilibrium point for the regulator. While these devices are effective, they lack the level of functionality available in an electronically controlled device.

Rotork Instruments, as part of their Fairchild brand, offers a series of electro-pneumatic pressure controllers that have built in PID closed loop microprocessor control utilizing a remote analog or digital setpoint signal. The electronic controller regulates feed and bleed solenoid valves to control pressure in the signal chamber of the booster section. Outlet pressure is measured and used as a feedback signal to the controller to provide accurate control of the outlet pressure. The device functions as a volume booster and I/P transducer.

Any of the devices can be controlled from the onboard keypad or a remote signal. A remote pressure sensor line can also be used with the controller to derive the feedback signal from further downstream from the instrument. This is helpful in eliminating pressure drop effects over the distance from the controller to an identified process point. The remote sensing also can improve system response. Adding the remote sensing is simple, just remove the factory installed plug and install an adapter that facilitates a line connection.

The various models are available with volume booster sections rated for 1 to 700 SCFM. More detail is found in the specification sheet provided below. Share your pressure control challenges with process measurement and control specialists. Leverage your own knowledge and experience into an effective solution with their product application expertise.

Electro-Pneumatic Pressure Controller and I/P Transducer from MSJacobs-Cali

I/P and E/P Transducers

I/P and E/P transducers deliver a pneumatic output
proportional to an electronic input signal.
Image courtesy Rotork Instruments - Fairchild

Converting from one signal type to another is a common challenge in process control. When the application calls for conversion from an electrical signal, current or voltage, to a pneumatic signal (pressure), this calls for an I/P or E/P transducer.

I/P and E/P transducers are electro pneumatic devices that convert current or voltage input signals to a linearly proportional output pressure. These transducers are available in a wide array of configurations to accommodate almost any industrial setting or application.

The transducers pictured use, in the pilot stage, electronic closed loop feedback and a piezoceramic actuator flapper nozzle system, controlling the signal pressure of an integral pneumatic volume booster. A control diaphragm and main valve on the volume booster section controls the flow of air at the output in response to the pressure received from the pilot stage. The output pressure of the volume booster is feed into an electronic closed loop feedback arrangement to deliver accurate pressure control.

Applying the transducer is a straight forward operation, involving matching the device input and output signal capabilities with those of the application. More detail is provided in the document included below.

Share your process measurement and control challenges with instrumentation specialists, combining your process expertise with their product knowledge to produce effective solutions.

Electro-Pneumatic Transducer for Process Control from MSJacobs-Cali

Pneumatic Volume Booster Function

Pneumatic Volume Booster
Fairchild

A volume booster is used in a pneumatic control system to relay a low flow signal as one with greater flow volume. The common configuration is to provide a 1:1 ratio between the input and output pressure, keeping the input and output signals the same pressure. Products are available that deliver different ratios.

The general purpose of a volume booster is to provide a relay between a system with low flow volume and one with higher volume requirements. A typical example is a pneumatic actuator. The flow available through the pneumatic signal line may be insufficient to deliver the response rate desired from the pneumatic actuator. A volume booster, with control over an independent air supply, solves this challenge with increased flow volume at the same pressure as the control signal.

Volume boosters are simple in operation. The input signal applies force to one side of a diaphragm, the output pressure to the other. An imbalance between the two applied pressures will cause the diaphragm to move, changing the position of the valve and the outlet pressure until the two forces are again in balance. Little maintenance is required when the units are properly installed and supply air is of good quality.

The unit pictured is from Fairchild, a well recognized manufacturer of industrial pneumatic components, and provides a 1:1 ratio. There are some key points in the selection process, so reach out to a product specialist with your pneumatic system challenges and requirements. Combining your process and facility knowledge with their product application expertise will produce effective solutions.

Volume Booster for Pneumatic Control Signal from MSJacobs-Cali

Volume Booster Working Principle

Pneumatic Volume Booster
(Fairchild)

A pneumatic air volume booster reproduce a low flow control signal with a higher regulated flow output pressure. It uses an unregulated input pressure to maintain a regulated output pressure under flowing and non-flowing conditions.

The volume booster is connected to the supply line and the output plumbing. It receives a pneumatic control signal, however, from another device, such as a transducer, valve positioner or other control means.

This pneumatic signal controls the pressure into and out of the booster, while allowing the booster to flow the maximum volume of the supply line. Boosters may also be referred to as pilot-operated regulators, as your control or pilot signal maintains the pressure control.

The regulated output of a pneumatic air volume booster can be any of the following:

• A direct reproduction of the pneumatic control signal
• A multiple of the pneumatic control signal 
• A fraction of the pneumatic control signal

The volume booster ratio is the multiplier or divider of signal pressure to output pressure. For example, a 2:1 ratio means output pressure is 1/2 the signal pressure. Similarly, a 2:1 ratio would provide output pressure twice the signal pressure. Note, however, the output pressure can never exceed the supply pressure to the booster.

Often the signal pressure is lower than the supply pressure because a control device (valve positioner, I/P, etc.) will only handle a lower supply pressure.