Armfield Engineering Education

PROCESS CONTROL TECHNOLOGY

PCT40 Multifunction Process Control Teaching System - issue 3

The Armfield PCT40 system provides a cost-effective way of teaching a wide range of process control techniques in a simple basic unit. More advanced aspects of process control can be addressed by adding optional extras to the basic system.

Ordering Specification

• A multi-function process control teaching system, capable of demonstrating level, flow, pressure and temperature control loops
• Desk top mounted and includes a built in USB computer interface
• Options include: reactor vessel with conductivity measurement, pH measurement, pneumatic control valve and electronic console
• Includes the following process control demonstrations:

Process principles

‚ Calibration of sensors (via PC software)
‚ Inflow cand outflow
‚ Outflow control
‚ Direct heating
‚ Indirect heating
‚ Batch and continuous operation
‚ Effect of sensor lag

Measured variables

‚ Level - on/off switch (fixed hysteresis)
‚ Level - differential on/off switch (adjustable hysteresis)
‚ Level - proportional pressure sensor (slow system response)
‚ Flow - Proportional turbine sensor
‚ Temperature - on/off switch (fixed hysteresis)
‚ Temperature - proportional thermocouple sensors
‚ Static pressure - proportional sensor (fast system response)
‚ Differential pressure - proportional pressure (fast system response)
‚ Conductivity - proportional sensor
‚ pH - proportional sensor

Controller types

‚ Manual control
‚ Effect of reverse/direct action
‚ PID proportional output with adjustable P, I & D terms
‚ Remote set point control
‚ Ratio, cascade and feedforward with feedback loops

Capabilities

> The basic PCT40 is used under computer control to demonstrate a variety of single control loops. It can be quickly reconfigured between processes, such as level control, temperature control, flow control and pressure control. The advanced software allows the student to change the control parameters, record results and analyse the results for the different configurations

> The PCT41 expands on the capabilities of the PCT40, and offers a wider range of control loops and strategies, including remote set points, dual loops, fluid property control (using conductivity). Again all these are under software control

> Other Accessories are available, including a control console with commercial PID controller, plus a pH probe and a pneumatic valve for those wishing to implement specialised demonstrations

> Large range of demonstrations from straightforward hardware

> Computer control as standard

> Computer generated loop disturbances for repeatability, allowing small variations in control parameters to be investigated

> Flexible system, suitable for project work

Description

PCT40 Basic Process Control 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 non-dedicated 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 are brought to a connection manifold, which uses self-sealing quick release fittings. This allows 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, i.e. 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 allows for a wide variety of different disturbances to be applied to the loops to allow 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 allowing 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 flowrate by varying pump speed
> Temperature of water in a vessel by varying the heater power
> Temperature of water heated indirectly by varying the flowrate

(All these loops are under software control)

Software Capability

The system is supplied with a complete educational software package with a wide range of facilities and functions. For most applications the computer is the primary interface between the user and the equipment.

The software displays real time process mimic diagrams, with readings of the relevant sensor outputs, and controls for the system inputs. The on/off, time proportioned and PID control algorithms are accessible through 'pop-up' control boxes, which give the user access to all the key control parameters, including the proportional band, the integral time and the derivative effect.

The software is supplied with detailed mimic diagrams, and full instructional help texts for ten predetermined student exercises when using PCT40 and an additional four exercises when using PCT41. These predetermined strategies have been carefully chosen to illustrate a wide range of the system capability and possible control strategies, i.e. level, flow, temperature, pressure, fluid characteristics, single PID loops, cascade and multiple loops, remote set points, etc. However, because of the flexibility of the system, many more control situations are configurable than it is possible to provide predefined student exercises for. Because of this, Armfield have included a user configurable option with the software, which allows the full range of capability from the system to be explored. This is particularly useful for student project work. Whichever configuration is being used, the software provides powerful data logging and graph plotting facilities, together with sensor calibrations and a wide variety of display and data export options.

The computer communicates to the PCT40 using a standard universal serial bus (USB) interface.

When used with the PCT43, the software also provides a simple SCADA demonstration. The process is controlled using the PID controller in the PCT43, but the P, I & D values can be accessed and varied by the computer, using the RS232 interface. At the same time the status of the process can be displayed on the computer by using the USB interface for data logging only.

Universal Software Interface

For users who wish to write their own software, e.g. in Matlab or LabView, full instructions are given for communications with the PCT40 via its built in USB interface. Advanced users are also given the facility to include their own process control algorithm, written in a suitable language such as C++. This is useful for exploring advanced and non-linear control systems.

EQUIPMENT SELECTION

Computer control Hardware control
Single loop Multi-loop Remote set point Single loop
Level PCT40 - - PCT40 + 43
Flow PCT40 - - PCT40 + 43
Temperature PCT40 - - PCT40 + 43
Pressure (basic) PCT40 - - PCT40 + 43
Pressure
(using Pneumatic control valve) PCT40 + 44 - - PCT40 + 43 + 44
Fluid Property (conductivity) PCT40 + 41 PCT40 + 41 PCT40 + 41 PCT40 + 41 + 43
Fluid Property
(pH) PCT40 + 41 + 42 PCT40 + 41 + 42 PCT40 + 41 + 42 PCT40 + 41 + 42 + 43

Requirements

Requires: Personal computer or PCT43

Cold water supply

(1.5 l/min at 2 Bar gauge)

Single-phase electrical supply (see below)

Order Codes:

PCT40-A 220-240V, 50Hz
PCT40-B 110-120V, 60Hz
PCT40-G 220V, 60Hz

Computer Requirement

The system is designed to be used with a personal computer (not supplied). The computer must have a USB connection available, and run Windows 98 or above.

Shipping Specification

Volume: 0.56m³
Gross weight: 35kg

Overall Dimensions

Height: 0.7m
Width: 1.0m
Depth: 0.54m

Extended 2 year Warranty on all Armfield Products

DATA SHEET

PRODUCT CATEGORY:
Engineering Education