The Essentials of Process Control (EPC) range of products takes students through the fundamentals of principles of process control, and progresses to give them a thorough grounding in the control of physical processes. Four independent process units demonstrate level, flow, temperature and pressure as the controlled variable. The concepts of closed loop control, including on/off control, proportional control, proportional/integral and proportional/integral/derivative (PID) control can be explored and demonstrated. Some units also cover both time proportioning and analogue control of the same parameter. To demonstrate industrial control systems, two further controlling devices are available, a full function industrial PID controller with autotune, and a programmable logic controller (PLC).
PCT50 is a highly visible and easy to understand water level control process. It comprises two clear acrylic tanks; a process tank mounted above a sump tank. Water is pumped up to the process tank and drains back to the sump tank via two valves, one manually variable and the other switched by software. Each valve can also be fitted with different-sized external orifices to change their characteristics. This flexible arrangement allows a wide range of control scenarios to be set up, including two fundamentally different processes, ie:
Level control by proportionally varying pump speed (Inflow control)
Level control by time-proportioned opening of a solenoid valve (Outflow control)
When using inflow control, repeatable disturbances can be implemented using the solenoid valve, and varied by using different orifice sizes. When using outflow control the pump speed can be stepped to provide a full range of repeatable disturbances. These techniques allow direct comparison of different controller settings.
PCT51 is a visible and easy to understand water flow control process. Water stored in the sump tank is pumped through a parallel pipe arrangement mounted on the lid of the tank and returns to the tank via two outlets, a software switched divert valve prior to the flowmeter and a manually operated variable valve after the flowmeter. Both outlets also incorporate interchangeable orifices to vary their characteristics.
The PCT51 demonstrates flow control by varying pump speed. Repeatable disturbances can be implemented using the solenoid valve and a wide range of different control investigations can be implemented using the interchangeable orifices and adjustable valves.
The PCT51 is an ideal system for demonstrating the onset of instability, the importance of filtering on the sensor output, and the trade-off between filter weighting and proportional gain on stability.
PCT52 is a a visible and easy to understand temp-erature control process. A fan blows air over a heater with radial fins and through a vertical clear acrylic duct. Sensors measure the surface temperature of the heater and the air temperature in the duct. This allows two different control implementations to be demonstrated with very different parameters, ie:
In each case the temperature is controlled by varying the heater power and repeatable disturbances implemented by switching the fan speed, hence allowing direct comparison of different controller settings.
PCT53 is a highly visible and easy to understand pressure control process, which uses pumped water to generate air pressure in a closed tank. It comprises two clear acrylic vessels, an upper process vessel mounted above an open sump tank.
The process vessel is sealed and so the air inside the tank is pressurised as water from the sump tank is pumped into it. Water drains from the process tank back into the lower sump tank via two outlets, one continuous and one incorporating a remotely controlled solenoid valve. Both outlets incorporate interchangeable orifices plus a hand operated variable valve, allowing the flow of water to be varied continuously to suit particular demonstrations.
This flexible arrangement allows a wide range of control scenarios to be set up, including two fundamentally different processes, ie:
When using inflow control, repeatable disturbances can be implemented using the solenoid valve, and varied by using the different orifice sizes.
When using outflow control the pump speed can be stepped to provide a full range of repeatable disturbances. These techniques allow direct comparison of different controller settings.
PCT 54 is an industrial PID controller incorporated in a console with input and output connections and controls on the front panel, designed primarily for use with the Armfield EPC series of process control products but suitable for use as a general purpose PID controller. It is supplied preconfigured for proportional analogue PID control, but can be reconfigured to give time-proportioned control using a digital output. The user has full access to the configuration of the controller menus via the buttons on the front or using a USB connection to a PC.
An additional analog output and digital switch allow an uncontrolled device on the process, such as a water pump or solenoid valve, to be operated remotely allowing disturbances to be applied to the process.
PCT 55 is a programmable logic controller (PLC) with graphical touch screen control panel designed primarily for use with the Armfield EPC series of process control products, but can also be used to control other items. It is supplied with PID control algorithms implemented in ladder logic ladder logic and configured to suit each of the EPC processes.
The user has full access to all the software and algorithms with the following features:
PCT56 is a trainer designed to introduce the essentials of signal conditioning applicable to process measurement sensors. It comprises an electronic console with inputs for sensors with three different types of electrical output, voltage current and resistance. The resistance input can be configured as two-terminal or a four-terminal bridge drive.
Controls on the console allow for ranging, fine scaling and offsetting of the measured values, the output being displayed on a 3.5-digit LCD display. Terminals allow the voltages to be monitored at each stage (voltmeter required). Thus many different sensors with different electrical outputs can be investigated and calibrated on this equipment.
For training purposes, the PCT56 is supplied with three pressure sensors of the same range, but different electrical outputs, plus a simple pressure vessel which can be pressurized using a hand pump.
The pressure vessel also incorporates a fitting for a reference instrument, such as the Armfield H12-8 digital pressure meter. The calibration vessel is fitted with a direct reading Bourdon gauge to give continuous indication of pressure inside the vessel for safety purposes.