An automatic sequential control system may trigger a series of mechanical actuators in the correct sequence to perform a task. For example various electric and pneumatic transducers may fold and glue a cardboard box, fill it with product and then seal it in an automatic packaging machine.

In the case of linear feedback systems, a control loop, including sensors, control algorithms and actuators, is arranged in such a fashion as to try to regulate a variable at a set point or reference value. An example of this may increase the fuel supply to a furnace when a measured temperature drops. PID controllers are common and effective in cases such as this. Control systems that include some sensing of the results they are trying to achieve are making use of feedback and so can, to some extent, adapt to varying circumstances. Open-loop control systems do not directly make use of feedback, but run only in pre-arranged ways.

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How can control system help in your home ?

AMX Touch-Screens and Touch-Panels canbe used to control multiple zones ofdistributed audio and video, as well asadaptable scene lighting design, therebyproviding the potential for infinitecreativity and variety in different areas ofthe home. It can also maintain homesecurity by automatically locking andunlocking windows, doors and gates, andby managing CCTV and intercom hardwareand operating systems.

The same controls can also oversee yourheating, ventilation, and air conditioningprogrammes, using pre-programmedsettings to guarantee appropriatetemperatures at given times of day, oraccording to the particular demands ofindividual rooms.

The system allows you to program highlypersonalized sequences of events to suityour own aesthetic and securitypreferences.

Remote Access to your Home
Another important feature of the system is the ability to access, surveyand control elements of your home from anywhere in the world via theinternet, which has incredibly important implications for security, homemaintenance and peace of mind.

AMX Home Control System brings an Extravagant Simplicity to the combinedpower of your 21st Century technologies, with a beautifully simple interfaceand a reduced number of menu options for what would otherwise be a longand complicated checklist of processes.

Contact us for Consultation about AMX control system compatiblity with your home .

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How can Metreau Keypads help ?

The Metreau Keypad line features a navigation wheel. An innovative, new interface feature that is designed to simplify the way people interact with, and use, the keypad. The wheel provides a natural and intuitive way to expand the keypad's functionality. Simply turn the wheel to the left or right to quickly and easily adjust audio volume, lighting levels and more, or press the top, bottom, left, right or center of the wheel to activate, set or select any level or function. This new interface feature is also incorporated into AMX’s new 5.2" Widescreen Modero® ViewPoint® Touch Panel (MVP-5200i).

Metreau Keypads provide a full range of control for virtually any device on the AMX AxLink™ Control Network – no matter how large or small the installation. For example, a Metreau Keypad can be used in conjunction with an AMX NI-700 NetLinx® Integrated Controller to provide full audio/video and environmental control for a single-room, such as an office, meeting space or classroom. The keypads can also be used to communicate with an AMX Control System in larger, multi-room environments such as homes, hotels, offices and government facilities. Metreau Keypads are available in six-button with navigation wheel, seven-button and 13-button configurations.

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How can Modero Touchscreen Panels help ?

The wireless model gives all the power and control of an AMX control system in a screen that can be used anywhere around the house. With two docking options, in-wall and desktop, the Wireless model can be used as the main control interface in large projects or used as a mobile controller anywhere around the house .

With the ability to display streaming video and the recent introduction of VoIP intercomm functionality it is an incredibly capable panel.

AMX have launched a range of new wireless panels to join the MVP range. The MVP 5200i launched in 2008 features a 5.2" screen, improved battery life, VoIP capability and looks gorgeous. 2009 launches see a couple of panels that share the basic form factor but shed some features to extend the appeal of this range to a wider audience.

AMX panels go up to 17" in size. The larger AMX models are very versatile control devices in rooms that can accommodate them.

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Elements of Control System

A typical AMX system consists of the following elements:

Controller/Cardframe - The central "component" of the AMX system. Commands are relayed to it via the interface devices, and the Controller/Cardframe executes the commands to the required devices. A controller contains a variety of fixed devices such as Relays, Infrared Emitting ports, Simple I/O ports, and RS232/422/485 ports. A cardframe is like an empty controller, in which one adds any combination of ports, relays, modems, and other devices

Input Device - Sends commands to the controller and also potentially receives feedback from the controller and / or the Controllable Devices. Input devices can take the form of Touch Panels directly wired to the controller or increasingly running Wireless communication either WiFi RF or ZigBee, or simple push button panels. The latest generation of AMX Modero Touchpanels offer the ability to display video, play audio and deliver VOIP Intercom functionality. The modern Netlinx Controllers are also controllable over IP by means of Java Applets emulating the touchpanel's display. (Internet/LAN/WLAN) This has excellent benefits ranging from being able to control remote classrooms from the other side of the world to being able to switch on your porch light while you are away on a vacation

Controllable Devices - The devices the AMX controller has been programmed to control, items such as Televisions, VCR's, Projectors, Teleconfrencing equipment, Lighting control systems, HVAC and Security systems etc. IP enabled devices such as Media Servers can provide rich two way communications with the AMX Controller or processor allowing a user to browse, manage and control a digital media library of audio and video files with full metadata, cover art etc

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Which kinds of controls are managed in Control Systems?

Logic control
Pure logic control systems were historically implemented by electricians with networks of relays, and designed with a notation called ladder logic. Today, most such systems are constructed with programmable logic devices.

Logic controllers may respond to switches, light sensors, pressure switches etc and cause the machinery to perform some operation. Logic systems are used to sequence mechanical operations in many applications. Examples include elevators, washing machines and other systems with interrelated stop-go operations.

Logic systems are quite easy to design, and can handle very complex operations. Some aspects of logic system design make use of Boolean logic.

On-off control
For example, a thermostat is a simple negative-feedback control: when the temperature (the "measured variable" or MV) goes below a set point (SP), the heater is switched on. Another example could be a pressure-switch on an air compressor: when the pressure (MV) drops below the threshold (SP), the pump is powered. Refrigerators and vacuum pumps contain similar mechanisms operating in reverse, but still providing negative feedback to correct errors.

Simple on-off feedback control systems like these are cheap and effective. In some cases, like the simple compressor example, they may represent a good design choice.

In most applications of on-off feedback control, some consideration needs to be given to other costs, such as wear and tear of control valves and maybe other start-up costs when power is reapplied each time the MV drops. Therefore, practical on-off control systems are designed to include hysteresis, usually in the form of a dead band, a region around the set point value in which no control action occurs. The width of dead band may be adjustable or programmable.

Linear control
Linear control systems use linear negative feedback to produce a control signal mathematically based on other variables, with a view to maintaining the controlled process within an acceptable operating range.

The output from a linear control system into the controlled process may be in the form of a directly variable signal, such as a valve that may be 0 or 100% open or anywhere in between. Sometimes this is not feasible and so, after calculating the current required corrective signal, a linear control system may repeatedly switch an actuator, such as a pump, motor or heater, fully on and then fully off again, regulating the duty cycle using pulse-width modulation.

Proportional control
When controlling the temperature of an industrial furnace, it is usually better to control the opening of the fuel valve in proportion to the current needs of the furnace. This helps avoid thermal shocks and applies heat more effectively.

Proportional negative-feedback systems are based on the difference between the required set point (SP) and measured value (MV) of the controlled variable. This difference is called the error. Power is applied in direct proportion to the current measured error, in the correct sense so as to tend to reduce the error (and so avoid positive feedback). The amount of corrective action that is applied for a given error is set by the gain or sensitivity of the control system.

At low gains, only a small corrective action is applied when errors are detected: the system may be safe and stable, but may be sluggish in response to changing conditions; errors will remain uncorrected for relatively long periods of time: it is over-damped. If the proportional gain is increased, such systems become more responsive and errors are dealt with more quickly. There is an optimal value for the gain setting when the overall system is said to be critically damped. Increases in loop gain beyond this point will lead to oscillations in the MV; such a system is under-damped.


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Types of Control System?

As well as the basic control-loop system, there are also different types of control systems that may be used for more complex processes.

The most common types are:

Sequence controllers

Distributed control systems (DCS)

Supervisory control and data-acquisition (SCADA) systems

Sequence Controllers
On many industrial sites electronic relays and simple on-off controllers are used to sequence regulator movements eg valves opening and closing.

These systems are gradually being replaced by sequence controllers based on as programmable logic controllers (PLCs).

They have a modular design so they can be expanded to cover more areas of the process operation as it becomes automated

They can also incorporate advanced types of controllers

Distributed control systems
These are normally used to control large or complex processes.

They are modular systems that allow operators to adjust the set points of many individual controllers from a central control.

A central control unit monitors the operation of each of the other controllers and makes data available to other high-level systems, such as fault diagnosis, process optimization and production-scheduling systems.

Supervisory control and data-acquisition systems
Supervisory control and data-acquisition (SCADA) systems can be used to control a wide range of industrial processes and are often used to provide an operator interface for PLC-based control systems.

They are software packages designed to run on a computer, with facilities for storing data for analysis.

Advanced SCADA systems also incorporate advanced control algorithms that can help operators to automatically optimize process operations.

Some advanced SCADA systems also include fault diagnosis and production scheduling systems.

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2 Types of Controller's Loops

Open Loop Controller
An open-loop controller, also called a non-feedback controller, is a type of controller which computes its input into a system using only the current state and its model of the system.

A characteristic of the open-loop controller is that it does not use feedback to determine if its input has achieved the desired goal. This means that the system does not observe the output of the processes that it is controlling. Consequently, a true open-loop system can not engage in machine learning and also cannot correct any errors that it could make. It also may not compensate for disturbances in the system.

For example, an irrigation sprinkler system, programmed to turn on at set times could be an example of an open-loop system if it does not measure soil moisture as a form of feedback. Even if rain is pouring down on the lawn, the sprinkler system would activate on schedule, wasting water.

Open-loop control is useful for well-defined systems where the relationship between input and the resultant state can be modeled by a mathematical formula. For example determining the voltage to be fed to an electric motor that drives a constant load, in order to achieve a desired speed would be a good application of open-loop control. If the load were not predictable, on the other hand, the motor's speed might vary as a function of the load as well as of the voltage, and an open-loop controller would therefore not be sufficient to ensure repeatable control of the velocity.

An example of this is a conveyor system that is required to travel at a constant speed. For a constant voltage, the conveyor will move at a different speed depending on the load on the motor (represented here by the weight of objects on the conveyor). In order for the conveyor to run at a constant speed, the voltage of the motor must be adjusted depending on the load. In this case, a closed-loop control system would be necessary.

An open-loop controller is often used in simple processes because of its simplicity and low-cost, especially in systems where feedback is not critical. A typical example would be a conventional washing machine, for which the length of machine wash time is entirely dependent on the judgment and estimation of the human operator

Close Loop Controller
Systems that utilize feedback are called closed-loop control systems. The feedback is used to make decisions about changes to the control signal that drives the plant. By contrast, an open-loop control system doesn't have or doesn't use feedback.

A basic closed-loop control system is shown in Figure 1. This figure can describe a variety of control systems, including those driving elevators, thermostats, and cruise control.

Closed-loop control systems typically operate at a fixed frequency. The frequency of changes to the drive signal is usually the same as the sampling rate, and certainly not any faster. After reading each new sample from the sensor, the software reacts to the plant's changed state by recalculating and adjusting the drive signal. The plant responds to this change, another sample is taken, and the cycle repeats.

Eventually, the plant should reach the desired state and the software will cease making changes.

If feedback indicates that the temperature in your home is below your desired set point, the thermostat will turn the heater on until the room is at least that temperature. Similarly, if your car is going too quickly, the cruise control system can temporarily reduce the amount of fuel fed to the engine.


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