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In this assignment I shall be looking at the differences between open loop control systems, closes loop control systems and also looking at and identifying the input, output and feedback gained.
The open loop control system is the cheapest form of control system you can have, this is due to its simplicity. The open loop control system has absolutely no artificial intelligence or any form of sensor what so ever. This then means there is nothing controlling the inputs going in to the system, this then means that accuracy may be deficient and the system will not be working to its true efficiency.
An example of this kind of system would be that for a microwave. When we turn a microwave on we select the power we want and the time limit we want and away it goes. The thing is, when it is powering itself up, how does it no if it’s hitting the true temperature we wanted successfully? The answer to this is that is doesn’t.
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.
The closed loop control system is rather more expensive to implement than that of its counterpart. This is down to the complexity of the functions that it can complete. The closed loop does have some form of monitoring capabilities and can in fact use sensors ad artificial intelligence well. An example of a closed loop control system would be that of the sprinkler system, where the user sets the desired time for the sprinkler to come on, but instead of juts doing this when set it could read the grass moisture in the first place and then make a split decision in whether it needed to be implemented or not.
Normally an open loop control system comprises of the following three things,
There are two differing types of systems that can be used for control and they are Analogue or digital. The two shall be explained in greater detail below.
The digital control system is used in the form of a micro controller to control a computer system. A digital controller is usually cascaded with the plant in a feedback system. The rest of the system can either be digital or analog. Some examples of analog systems with a digital feedback controller are:
For mixed control types such as digital and analogue systems we need a process of conversion, for example digital to analogue converters (these are called DACS). The opposite can take place, by using an analogue to digital conversion process called ADC.
All of these analogue control systems are embedded with micro controllers. These micro controllers have the power to run the systems and comprise of fairly common hardware properties. The typical hardware properties that can be found in the control systems micro controller can be seen below;
A micro processor will control the control system and process the information in order for it to function correctly. For example, if we have a sprinkler system in the garden as previously described, the inputs and outputs would need to be managed by the micro controller. If the ground was wet, it could check its EPROM (erasable program read only memory) to see what the water density was, and then the process could make a decision and process it appropriately. Below is a list of the inputs that could be put in to this system.
Usually the forms of input found in the analogue systems are called transducers. There is a specific purpose to doing this and its main reason is down to conversion. If for example we have an electrical input and we want to display it as a picture on the page we must use a television. The transducer in this will be the Cathode ray tube (CRT) which is electromagnetic.
When using sensors or transducers the signal must be converted in to an electrical measurement (volts). Below is a list of the possible input devises we can have within a system or a circuit.
When the electrical charge is received it then needs to be converted in to the correct signal type using one of the transducers above, however for these signals to be used correctly we need to obtain the appropriate components.
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