Control & Instrumentation

Transcription

1 Control & Instrumentation Control & Instrumentation! Analogue & Digital Servo Trainer! Modular Servo System! Transducers kit! Programmable Logic Control Applications! Dual Conveyor plc Workcell! Elevator! Digital Pendulum Control system! Magnetic Levitation System! Twin Rotor MIMO System! Precision Modular Servo Control Workshop! Coupled Tanks System Control Engineering is of significant interest in most areas of industry - new and established. The Feedback range of Control Engineering training equipment has been designed to provide a modern, efficient approach to training the engineers and technicians working in this field. Feedback s philosophy is to equip students with the fundamental ideas and principles that underpin modern engineering practice by using versatile trainers that quickly and clearly demonstrate the required technology. Paramount to all Feedback equipment is the principle that students of Engineering and Technology should work with hardware and be allowed to take a hands-on approach. All of Feedback s teaching hardware is supported by extensive teaching and theoretical courseware, either in the form of paper manuals or software. Within the Control Engineering range, Feedback offers hardware that can be used in conjunction with a combination of:-! Conventional test and measurement equipment! Industry standard control devices! Computer Assisted Learning techniques with Feedback s Discovery software - offering on-screen instruction and embedded, real-time, virtual instrumentation! Sophisticated simulation software such as MATLAB to create challenging applications Benefits! Ideally suited for University and Technical College courses! MATLAB applications for real-time control! All products provided with in-depth teaching manuals or software! Compact, bench-top systems! Teaching material and applications relevant to industrial practice

2 Linear Servos Servo Fundamentals Trainer USB! Open and closed-loop speed and position control! Demonstrates both Analogue and Digital control techniques! Built-in PC based instrumentation! On-board square and triangle waveform generator! Independent single, two-term, or full PID control! Absolute position & incremental speed & position encoders! Continuous analogue position and velocity feedback signals! Linear or PWM motor drive! Switched faults throughout the system! LCD speed & digital voltmeter Analogue! Operational amplifier characteristics! Motor, tachogenerator and brake characteristics! Simple control & speed systems! Error channel and feedback polarity! Influence of gain! Velocity feedback! System following error! Speed control systems! Introduction to 3-term control! Applications of 3-term control! Single amplifier control circuits! Transient velocity feedback and derivative feedforward! Transfer functions & frequency response principles! Application of frequency response methods to the system Digital! A/D and D/A conversion! Motor control! Potentiometer position sensors! Digital encoders! Gray code encoder! Incremental encoder! Speed & directional encoding! Position control using analogue and digital sensors! Speed control using analogue and digital sensors! Position servo using P+D control! Position servo using P+I control! Position servo using PID control This trainer introduces the theory and practice of automatic control systems and allows investigation of open and closed loop analogue, digital, speed and position control. The system consists of three main units: Mechanical Unit: with input and output potentiometers, motor, tachogenerator, absolute and incremental encoder and on-board waveform generators. Analogue Unit: with four-input error amplifier. Optional additional time constant. Variable gain and velocity feedback. Single, two term or full PID control. Digital Unit: provides access to PC via a USB interface, has A/D and D/A converters, linear or PWM motor drive, LED display. Feedback Discovery software supports both the Analogue and Digital units and allows assignment work to be carried out with on-screen theory, background, practicals and questions. The three equipment package options are: USB Servo Fundamentals Trainer; comprising the Analogue Control unit, Digital Control unit and the Mechanical unit USB Analogue Servo Trainer; which is comprised of the Analogue Control unit and the Mechanical unit USB Digital Servo Trainer; which is comprised of the Digital Control unit and the Mechanical unit. All packages are supplied with dc Power Supply, interface cables, Discovery software and courseware. The software supplied with the Digital unit contains PC-based instrumentation, including a chart recorder. A Servo Fundamentals Trainer Upgrade Pack is also available for customers to upgrade their existing , enabling it to be connected to a PC using USB technology and Discovery software.

3 Linear Servos Complete Modular Servo System The Modular Servo System is a unique equipment designed to study the theory and practice of automatic control systems. It illustrates modern circuit and constructional techniques and has been used in technical Institutes and training establishments throughout the world for many years. The system is modular and very versatile, making it possible for individual units to be arranged to create operating block schematic systems. The system also provides a linear quantitative control application for more advanced work. The following systems are available: MS150 dc Modular Servo System; the basic dc set. MS150A ac Modular Servo System; the basic ac set. MS150-2 ac/dc Modular Servo System; the MS150-2 is used in more specialised and advanced control applications, some detailed knowledge of ac carrier systems is required. It is available as a stand-alone, complete system or by adding extra modules to the dc system. MS150-3 Complete Modular Servo System; in addition to the subject areas covered by the MS150 and MS150A, the full system allows additional subjects (see Curriculum) to be studied. Comprehensive assignment manuals are provided with each system. As well as the four main systems the modules are available separately and as two conversion kits as follows: Simulated Relay Unit SR150G Differential Synchro Unit DS150J Sample and Hold Unit SH150M Proportional, Integral and Derivative Unit PID150Y MS150 to Hybrid System Conversion Kit MS150RST MS RST to ac Operation Conversion Kit MS150UVW There is an Upgrade Pack PCI available for customers who would like to upgrade their existing MS150 system to a (see page 9). This enables an MS150 to be used with MATLAB software. dc Modular Servo System MS150! Operational amplifiers! Motor speed characteristics! dc error channel! Simple position control! Closed-loop position control! Simple speed control! Deadband & step response! Velocity feedback! Analysis of simple position control with speed response! Position response! Closed loop frequency response! Identification of motor time constants! Identification of velocity error constant Kv! Frequency and transient response! Measurement of following error! Stability considerations & the use of lead, lag and combined networks! Tachogenerator feedback and its effects on system performance including acceleration feedback! Linearisation of systems ac Modular Servo System MS150A! Motor characteristics! ac tachogenerator! Motor speed control! Characteristics of 2-phase motors! ac pre-amplifiers! Position control systems! Importance of phasing on torque and speed performance! Compensation using the adjustable notch filter! Notch filter design! Frequency selective characteristics for the elimination of noise and harmonics! Analysis of carrier systems! Frequency transformation for compensator techniques! Principles and measurement of compensation unit characteristics! Instability! Reduction in steady following error! Effects of gain and damping! Synchro link and the demodulator! Closed loop systems Complete Modular Servo System MS150-3! Relay characteristics and relay operated systems! Following characteristics of relay system! Effect of backlash on the system! Phase-plane analysis! PID control loop characteristics! Speed control! Position control! Following error! Waveform sampling! Sampled data servo control! Simulated sampled data control! Sampled data process control systems! Differential synchros

4 Transducers Transducers Kit TK & TK2942-1! Bench-top study of transducer applications! 28 proven student assignments! Manual covers theory, practice and industrial applications! Employs 14 common industrial transducers! Inclusive ac and dc instrumentation sections! Suitable for most engineering disciplines! Repeatable experimental results with minimum preparation time Electro-mechanical Transducers Utilising variation in resistance:! Wheatstone bridge! Amplifiers! Liquid depth and resistivity! Displacement! Strain Utilising variation in capacitance:! Wheatstone bridge for capacitance! Variable area and distance capacitive! Use with an oscillator and discriminator in FM systems Utilising variation in inductance:! Electromagnetic inductance! Variable inductance transducer! Mutual inductance transistor! Linear variable differential transformer! Transducer circuits Light Transducers! The nature of light! Photoconductive cell! Semiconductor photodiode! Phototransistor! Spectral response Heat Transducers! Heat distribution! Thermocouples! Thermistors! Resistance thermometers! Temperature control (on/off)! Temperature control Many engineering applications and systems depend on accurate measurements and monitoring. Transducers are fundamental to the measurement process, consequently the study of different types of transducers, how they operate and how their output signals may be processed, is essential background knowledge for any engineer. The Transducers Kit introduce students to the concepts and understanding of common transducer devices and standard signal conditioning methods. They are available in three kits: Transducers Kit TK which comprises; the Measurements Package, Electro-mechanical, Heat and Light Transducers Kits, dc Power Supply with all leads, accessories and courseware, TK Complete Transducers Kit which includes the items in TK plus Function Generator, Timer Counter, Oscilloscope and Capacitance and Resistance boxes. There is also an Introduction to Transducers Kit TK2941 available which contains the TK2941E and TK2941M. The student manual contains 28 assignments, covering the use of all three Transducers Kits (TK2941E, 2941H and 2941L) and includes relevant theory and practical information. The Transducers Kit consists of a measurements package (containing a comprehensive instrumentation module and a test rig) and three self-contained transducers kits, which are all available separately but must be used with the Measurements package: Electro-Mechanical Transducers Kit TK2941E Includes six linear displacement transducers to be mounted on the test rig. n Linear variable resistor n Variable inductor n Variable area capacitor n Linear variable differential transducer (LVDT) n Variable distance capacitor n Strain gauge Heat Transducers Kit TK2941H Includes 4 thermal devices and a heat bar assembly with temperature gradient. n Thermistor n Platinum resistance n Bi-metallic switch n Thermocouple Light Transducers Kit TK2941L A light source and transducer box containing: n Photoconductive cell n Photodiode n Phototransistor Measurements Package TK2941M An instrumentation module with signal conditioning circuitry comprising: n Wheatstone Bridge n Oscillator n Operational Amplifier n Discriminator n Power Amplifier

5 PLC Applications Programmable Logic Control Applications ! Fundamentals of logic! Basics of PLC programming! Developing ladder logic programmes Automatic Washing Machine This process allows a sequence of events to be controlled. The development of several different programs is possible, which can be set-up as conditional jumps. Traffic Signal Control This application allows traffic light control of crossroads using a timed sequence. The control program can be developed to cope with interrupts from pedestrian crossing requests or off-peak vehicle detector inputs.! Programming timers! Setting initial conditions! Time-based process controls! Use of interrupts and emergency stop Dual Conveyor PLC Workcell ! Parts selection by logical detection! Induction and opto-electronic sensors! Component sort and assembly! Interfaces to most major types of PLC! Comprehensive courseware! Fundamentals of logic The Dual Conveyor Workcell is a complete system which can be used to develop the parts selection task into a simple assembly process. Plastic and metal components are selected by size and are fed onto the chutes for dispensing into a final assembly task where they are combined with a 2nd component. The finished product can then be sorted by material, assembly or type. The system allows complex control scenarios to be developed using combinations of timers and counters with master and zone control functions. An optional Diameter Gauging Unit is also available which can be added to the workcell to allow the diameter of any components on the conveyor to be measured. Using a similar system to the height detector, the unit provides three possible outputs: under size, over-size, or the logical NAND of the two providing one input to the PLC for correct sized components. The position of the parts probe is controlled by two sensors detecting top dead-centre of the drive cam. Acceptable tolerances for components can be preset. The addition of the second gauge unit allows programs of greater complexity to be developed. The programming of the detector is an excellent introduction to the use of logical detectors for in-process inspection and quality control. NB: The plc in the picture is not supplied with the equipment.! Basics of PLC programming! Developing ladder logic programmes! Programming timers! Programming counters! Structure of control systems! Sequencer programmes! Jump instructions and subroutines! Combined counter and timer functions! PLC installation practices

6 PLC Applications Elevator ! Fully working model of an elevator with four floors! Floor sensing and visual indication of direction of travel! Motorised elevator car door with internal illumination and audible sound to announce arrival at each floor! Normally on brake to hold car at desired floor! Up/down call buttons for each floor! Front panel manual switch for testing and debugging! Integral motor servo controller with mechanical brake! Elevators may be mounted side-by-side to demonstrate complex multi-elevator systems! Discrete motor interface for PLC logic only control: variable up/down speed at 100%, 60% and 30%! Built-in closed loop control with option to close the loop using external controller! Interfaces with most PLC types. Analogue control is also available! Load-cell indicates passenger loading in elevator car! Selection of weights to simulate varying passenger loads! Vertical travel limit switches! Analogue car position feedback signal! Switchable faults! Example code provided for Allen Bradley and Mitsubishi PLCs! Fundamentals of logic! Basics of PLC programming! Developing ladder logic programmes! Basic and advanced sequence control The elevator provides a sophisticated application to illustrate the principles of PLC interfacing and control based on a real-life application. Starting with simple programme sequences to control elevator speed, direction and floor arrival/ departure, the student can progress to advanced floor request handling and continuous (analogue) control with acceleration profiling and compensation for varying car loads. The elevator car moves between floors in response to requests from call buttons at each floor or within the elevator car (located on an external panel). Sensors indicate which floor the elevator car is at and provide advance warning to allow the car to be slowed prior to arriving at the destination floor. A brake allows the car to be held at a floor while the motorised car door is operated allowing the occupants to enter or leave. An audio sounder is provided to announce arrival at a floor. The internal controller unit provides closed-loop motor speed control with both logic & analogue interfaces so the elevator can be controlled by a basic PLC with minimal digital I/O. More sophisticated control may be implemented using additional analogue I/O. An integral load-cell and motor position feedback can extend the application to continuous control. The load-cell indicates elevator car loading and a set of weights simulate varying numbers of passengers. The position feedback signal allows advanced control of the elevator car motion. List of Elevator I/O Digital outputs: Floor 1 up call button Floor 2 up call button Floor 2 down call button Floor 3 up call button Floor 3 down call button Floor 4 down call button Car floor 1 call button Car floor 2 call button Car floor 3 call button Car floor 4 call button Floor 1, 2, 3 & 4 sensor Car door open Car door closed Analogue outputs: Car speed Car position Car passenger load Digital inputs: Open/close car door Brake release Car going up indicator Car going down indicator Car on its way floor 4 down Car on its way floor 3 down Car on its way floor 3 up Car on its way floor 2 down Car on its way floor 2 up Car on its way floor 1 up Destination floor 4 (car indicator) Destination floor 3 (car indicator) Destination floor 2 (car indicator) Destination floor 1 (car indicator) Car 100%, 60% & 30% speed Car direction up/down Arrival bell Analogue inputs: Car speed demand Motor current demand

7 Advanced MATLAB Control Applications MATLAB Matlab SOFTWARE Control Applications using MATLAB MATLAB is a higher-level technical computing language that provides an environment for algorithm development, data analysis, data visualisation, etc. Together with SIMULINK and additional toolboxes it facilitates control system design and analysis, which can later be implemented in real-time applications using Real-time Workshop. With an Advantech PCI card this creates an impressive digital control system development environment. Feedback Instruments control applications are designed to be compatible with such an environment. Using the detailed training manuals the user is guided through the design process within MATLAB. The following crucial development steps are described: " Phenomenological process models " Dynamics analysis " Discrete models identification " Controller design " Controller tests on the model " Controller implementation in real-time applications " Implementation of various control strategies " Data visualisation The Phenomenological process models are designed in SIMULINK to provide initial models for the user to test. Model linearization is then discussed and the use of simple dynamics analysis - like bode diagrams poles and zeros maps are introduced. To obtain accurate models Identification procedures incorporating MATLAB functions are described. The user has a chance to go step-by-step through the discrete models identification. One of the obtained models is used for the Controllers design and PID control is explained. A guide is given for PID controller design, testing, tuning and implementation on the model. Root locus technique is used to illustrate the changes that PID controller tuning inflicts on the control system performance. The designed controllers are prepared in SIMULINK to be built and tested through the Real-time Workshop using the Feedback control applications. The series of assignments provide a comprehensive course, and the user has a choice of using the pre-written applications, according to the manual, or designing their own. Example of a self-designed control system Swing up, inverted pendulum, crane control time (sec) Setting-up the parameters to demonstrate control of the Pendulum cart Plot showing comparison between pendulum angle and corresponding control signal

8 Advanced MATLAB Control Applications MATLAB Matlab SOFTWARE Digital Pendulum PCI! Pendulum Description! Pendulum model! Equations of motion Nonlinear model! Linear models! Model identification Static friction compensation Running a real-time model! Dynamic model! Cart model identification! First model identification! Using the MATLAB system identification toolbox! Crane linear model identification! Inverted pendulum linear model! Pendulum set-up control! Plant control! PID controller! PID control of cart model position! Real-time PID control of cart position! Real-time swing-up control! Inverted pendulum control of swing-up! Inverted pendulum stabilisation! Crane control! Combined control techniques! Swing-up and hold! Up and down model The Digital Pendulum is a modern version of a classical control problem; that of erecting and balancing a free swinging pendulum in its inverted position or moving a hanging pendulum in a controlled manner. The cart on the track is digitally controlled to swing up (SELF ERECTING) and to balance the pendulum into an upright sustained position or to move the cart with pendulum in an unperturbed down position. The cart track is of limited length, imposing constraints on the control algorithm. In pendulum mode the system is used to control the twin arm pendulum from an initial position, hanging at rest with the cart in the centre of its travel along the track, to a final position with the pendulum upright and the cart restored to its central position. In crane mode the control problem is to move the position of the cart without undue movement of the pendulum. This problem is typical of that experienced when controlling a gantry crane. Magnetic Levitation System PCI Analogue operation! Non-linear model! Unstable system! Linearisation about an operating point! Infra-red sensor characteristics! Lead-lag compensation! Perturbation sensitivity! PD control Digital operation! Unstable system! Linearisation about an operating point! Non linear model! A/D and D/A conversion! State space PD control! PID control! Calibration! Regulation and tracking control This classic magnetic levitation control problem is now presented in a new and innovative form. A 25mm diameter, hollow steel sphere is suspended in space with visually appealing results and convenient time constants. Both analogue & digital control solutions are implemented. Convenient sockets on the enclosure panel allow for quick changes of analogue controller gain and compensation components. The equipment is self-contained in analogue mode, with built-in power supply. In the digital mode the system operates within a MATLAB environment which allows the system parameters to be determined and the system to be modelled. Once the digital controller parameters have been determined, the controller can be used to run the hardware and the actual control performance can be seen and analysed.

9 Advanced MATLAB Control Applications MATLAB Matlab SOFTWARE Twin Rotor MIMO PCI The Twin Rotor System demonstrates the principles of a non-linear MIMO system with significant cross-coupling. Its behaviour resembles a helicopter but the angle of attack of the rotors is fixed and the aerodynamic forces are controlled by varying the speeds of the motors. Significant cross-coupling is observed between the actions of the rotors, with each rotor influencing both angle positions. The MATLAB software allows the student to design and test stabilising controllers with independent control applied to each co-ordinate of the system. More advanced investigations may be carried-out through user-defined algorithms from within SIMULINK.! 1-Degree of Freedom (DOF) PID stabilising and tracking horizontal controller! 1-DOF PID stabilising and tracking vertical controller with gravity compensation! 2- DOF PID stabilising and tracking controller! Parameter tuning! Coupled dynamics analysis! Dynamics decoupling! Phenomenology analysis! Model identification Precision Modular Servo Control Workshop PCI Analogue servo operation! Open-loop systems Speed/ Position! Closed-loop systems Speed/ Position! Motor characteristics! Frequency and Step response measurements Digital servo operation! Real-time digital control! PID controller design! Adaptive control The Precision Modular Servo Workshop has been designed to give a rapid and direct path from control system design to hardware implementation. The resolution and accuracy of the system, and the consistency of its performance, makes the Precision Modular Servo Workshop ideal for serious study of digital linear servo control systems. As well as allowing study of digital control the Precision Modular Servo Workshop also provides a complete introduction to servos, from fundamental studies of analogue servos through to full, real-time digital control using MATLAB, SIMULINK, Real-time Workshop and Real-time Windows Target. It is fully supported with laboratory assignments which have been designed to give students a full understanding of the control paths within the equipment. For those customers who wish to upgrade their existing MS150 system to a there is an Upgrade Pack PCI comprising a Incremental Encoder, D/A, A/D Converter, software, cables and Courseware.! Precision Modular Servo (PMS)! Testing the dc motor model! PMS model identification! Static friction compensation Model 1 & 2 identification! PMS set-up control! Plant control! PID controller! PMS velocity control PID control of motor velocity Real-time PID control of motor velocity! Control signal saturation Anti wind-up design Anti wind-up for PMS! PMS position control! PID control of motor position! Real-time PID control of motor position! Position tracking! PMS control under variable load conditions! Simple gain scheduling algorithm! Gain scheduling

10 Advanced MATLAB Control Applications MATLAB Matlab SOFTWARE Coupled Tanks System ! Fully compatible with MATLAB and SIMULINK! Self-contained unit can be either floor or bench mounted! Four tanks each with pressuresensor water level measurement and easy-to-read visual scale! Two independently controlled pumps allow variable flow control! Easy to configure coupling between tanks allows for a wide range of control scenarios from basic to advanced level! Can be configured as Single Input Single Output (SISO) or Multiple Input Multiple Output (MIMO) system! System dynamics can be modified using easy to change orifice caps! Nonlinear model! Linearisation and linear model simulation! 1 tank and 2 tank model identification! PID control of water level in top tanks! PID control of water level in bottom tanks! Parallel PID control in two double tank columns The Coupled Tanks set-up is a model of a chemical plant fragment. Often tanks are coupled through pipes and the reactant level and flow has to be controlled. The Coupled Tanks experiment is designed so that the system can be configured. The Coupled Tanks system has four translucent tanks each with a pressure sensor to measure the water level. The couplings between the tanks can be modified by the use of seven manual valves to change the dynamics of the system imposing the use of different controllers. Water is delivered to the tanks by two independently controlled, submersed pumps. Step disturbances generation is provided by four manual valves. Drain flow rates can be modified using easy to change orifice caps. The Coupled Tanks are controlled by using SIMULINK and an Advantech PCI1711 Interface card. The user may build their own models or use the models supplied together with the curriculum. The process variables can be observed on-screen in plots. The product is supplied with comprehensive student manuals that provide information about the physical behaviour of the system models and guide the student through the control tasks. Control algorithms are developed, tested on the models and then implemented in a real-time application.! Cross-coupling introduction and analysis! Dynamics decoupling with cross-coupling identification! PID control with decoupling! Disturbance compensator with PID control

11 Associated Control Products Associated Control Products in the Feedback range ac Process Motor Control Speed Control ASC Feedback also offer a range of Process control trainers using industry relevant components (4-20mA signals). Control is achieved using an standard industrial controller providing a range of functions from simple 2-state to full PID. Discovery software is used to deliver the teaching material and display real-time measurements. ph Rig ! Uses industry standard Process Controller, 4-20mA signals and RS232/RS485 serial communication bus! Dual loop control! Typical Industrial Processes! Discovery software! Real-time measurements and Control Pressure Rig Processes Covered! Level & Flow! Temperature! Pressure! ph The Temperature Rig and Level & Flow Rig linked to the Forced Air Cooler Power Electronics The Feedback range of Power Electronics equipment covers thyristor control circuit principles and applications, through to the control of a dc motor, using Single and Three phase thyristor circuits.! Single and Three phase uncontrolled rectification! Single and Three phase controlled rectification! Single and Three phase motor speed and current control! Zero crossing, burst firing circuits! Four Quadrant control! Single and Three phase equipment Thyristor and Motor Control

12 Control & Instrumentation Ordering Information * Ancillary Linear Servos Servo Fundamentals Trainer USB Equipment B Analogue Servo Trainer USB B Digital Servo Trainer USB B Analogue & Digital Servo Fundamentals Trainer Upgrade Pack A B dc Modular Servo System MS150 ac Modular Servo System MS150A ac/dc Modular Servo System MS150-2 Complete Modular Servo System MS150-3 Upgrade Pack PCI A Transducers Transducers Kit TK Complete Transducers Kit TK Introduction to Transducers Kit TK2941 Electro-mechanical Transducers Kit TK2941E Heat Transducers Kit TK2941H Light Transducers Kit TK2941L Measurements Package TK2941M E Programmable Logic Control Applications Automatic Washing Machine B C Traffic Signal Control B C Dual Conveyor PLC workcell B C Elevator B C Advanced Control (MATLAB Applications) Digital Pendulum System PCI A D Magnetic Levitation System PCI A D Twin Rotor MIMO System PCI A D Precision Modular Servo Control Workshop PCI A D Coupled Tanks System A # B # when using MATLAB. Ancillary Equipment (see * reference above) A. A PC compatible computer - 1GHz Pentium 3 CPU or above, 512MB RAM, 2GB free hard disk space, CD drive and Microsoft Windows 2000 SP3 or SP4, or Windows XP SP2, 1 free full size PCI slot. B. A PC compatible computer - 1GHz Pentium 3 CPU or above, 512MB RAM, 2GB free hard disk space, CD drive and Microsoft Windows 2000 SP3 or SP4, or Windows XP SP2 with USB port. C. A PLC - Allen Bradley and Mitsubishi are supported. D. MATLAB and SIMULINK with Real-time Workshop and Real-time Windows Target. System Identification and control system toolboxes are recommended. E. dc Power Supply. Control & Instrumentation Printed in England Registered in England number A subsidiary of Feedback plc. Feedback reserves the right to change these specifications without notice. Feedback Instruments Limited Park Road, Crowborough, E. Sussex, TN6 2QR, England. Telephone: +44 (0) Fax: +44 (0) E mail: feedback@fdbk.co.uk Website: Feedback Incorporated 437 Dimmocks Mill Road, Suite 27, Hillsborough, NC 27278, USA Telephone: (919) Fax: (919) info@feedbackinc.com Website: