- Pneumatic control valve, AISI 316 stainless steel execution
- Bourdon spring pressure gauge, range 0-6 bar
- Electronic pressure transmitter
- AISI 304 stainless steel tank
- Plastic silencer
- PID microprocessor controller
- Power supply light
- measurement terminals for the 4-20 mA input signal of the controller
- measurement terminals for the 4-20 mA output signal of the controller
- Safety valve calibrated at 9 bar
Description of apparatus:
The unit enables to study the automatic pressure control using a line provided with a tank, a control valve, a pressure transmitter and a PID controller. The line is pressurized using compressed air. The plant is provided with specific supervision software, Mod. SWPCB/EV, that enables the use from P.C. The bench can be connected in series with Mod. FCB/EV.
Experiments done on it:This unit used to control the pressure of air inside the piping.
In this unit, the PID control is carried out on the air pressure inside the piping with possibility to insert a capacity into the circuit consisting in the tank D1. The control device consists in a pneumatic valve that, according to the signal coming from the PID controller, adjusts the compressed air flow rate at the system’s input. The electronic transmitter PT1, measures the pressure in the line and sends an electrical signal to the PID electronic controller.
The signal sent by the transmitter PT1 to the PID controller is compared to the set-point value set on the controller. At this point the controller sends a signal to the output, function (PID) of the shift between the value of the process variable and the set-point. Such electrical signal is converted by an electropneumatic converter into pneumatic signal controlling the opening level of the valve.
The signals and the input and output of the PID controller can be measured with a milliammeter using the proper terminals set on the board. The pneumatic signal at the output of the I/P converter can be read directly on the pressure gauge set on the board. The controller is set at the factory to PI mode (proportional + integrative) as in the pressure control the derivative action is generally not used.