Armfield - Process Control Technology - PCT40 Multifunction Process Control Teaching System

The PCT40 contains everything that is needed to perform a range of single-loop process control experiments in conjunction with a PC.

It includes a variable volume process tank, a hot water tank with electric heater and indirect heating/cooling coil, a hot water pump, two nondedicated pumps, three on/off solenoid valves and a proportioning valve. The instrumentation includes temperature sensors, two differential water pressure sensors, a mechanical level sensor (float switch) and an electronic level sensor (conductivity). The inlets and outlets of the various pumps, valves and tanks incorporate self-sealing quick-release fittings. This enables the configuration to be quickly changed, offering a wide variety of different loops.

The PCT40 includes a computer interface (USB), and all of the parameters can be controlled directly from the computer, (ie the pump speeds), the valve positions and the heater power. The computer also displays the readings from the various measurement sensors. The software supplied with the unit includes on/off, time proportioned and proportional/integral/derivative (PID) algorithms where all the parameters are easily accessed and adjusted by the user. This approach means that a separate electronic console is unnecessary for most applications.

The flexible nature of the system also enables a wide variety of different disturbances to be applied to the loops to permit the effectiveness of the control parameters to be compared. As all these disturbances are under software control, they can be repeated precisely during the optimisation process, thus enabling an excellent degree of fine-tuning to be implemented. A pressure regulating valve with filter is also included to isolate the equipment from fluctuations in the water supply pressure.

The type of loops achievable with the basic PCT40 include:

• Tank water level by varying input flow
• Water flow rate by varying pump speed
• Temperature of water in a vessel by varying the heater power
• Temperature of water heated indirectly by varying the flow rate

(All these loops are under software control)

The PCT41 extends the capability of the basic PCT40 by adding an additional process vessel, complete with a heating/cooling coil and a stirrer. The inputs and outputs incorporate quick release fittings, enabling the PCT41 to be added quickly and easily.

The PCT41 also includes a conductivity probe to enable cost-effective fluid property demonstrations to be performed.

The addition of the process vessel enables more complex process control problems to be addressed, including remote setpoint demonstrations. Again these all take place with the repeatability advantages that electronic and software control brings.

Additional loops that can be implemented with the PCT41 include:

Single loops in combination:

• Conductivity control of reactor contents by varying flow rate of one component
• Temperature control of reactor contents by varying heating fluid flow rate
• Temperature control of heating fluid by varying heater power

Remote setpoint control:

• Ratio control of two flows (Fig 1)
• Cascade control of conductivity and flow (Fig 2)
• Feedforward control of flow to flow
• Feedforward control of flow combined with feedback control of conductivity (All these loops are under software control)

The PCT41 includes a conductivity probe as part of the basic supply. This conductivity probe can be used to demonstrate fluid property control systems without the maintenance problems, which can be experienced with pH probes. However, as pH control is probably the most common industrial application of this type of control system, users may wish to implement true pH control loops. This can easily be implemented by adding the PCT42 pH Sensor Accessory to the combined PCT40 + PCT41 systems.

The PCT 43 is an electronic control console that can be used to control the PCT40 (+PCT41/42) instead of a computer. It includes controls for the pumps, valves and heater, plus a display for the sensors. It incorporates a commercial PID controller, complete with RS232 interface. Using this console also enables the sensor data to be logged and displayed on a computer (using the PCT40 USB interface), but with the control functions being implemented in the PCT43 hardware, rather than the computer software.

Facilities include:

• Use of a commercial PID controller
• Simple interfacing to other PLC and/or PID controllers
• Use of 4-20mA interfaces
• Use of serial communications (RS232) in a control system
• Simple SCADA demonstration (requires PC)

The PCT44 is a pneumatic control valve, plus associated components, for use with the PCT40/41 system. Retaining the flexible concept of the whole range, it can be plumbed into many of the flow control loops, and provides a good illustration of pneumatic valve technology.

Note: This accessory requires a compressed air supply