Chapter 16 Control Systems

• 1. What is a feedback loop?
  This is a signal that comes back to the computer (in a control system) from the equipment that is being controlled. As an example there will be a feedback signal from the motor that is opening an automatic door at a supermarket to make sure the computer program knows if the motor is opening or closing the door at any given time. Clearly, if the motor is already opening the door then there would be no need for the computer to send a signal to get the motor to start opening the door. When the door is open the computer might eventually send a new signal to the motor to get it to shut the door. It will only send the signal if the door is already open and is not in the process of shutting already. The status of the motor for controlling the door is sent to the computer via the feedback loop.
• 2. What is a control interface?
  A control interface is for ensuring that the sensors in a control system can communicate with the controlling computer. It is the purpose to change analog sensor signals into digital signals that can be used as input for a controlling program.
• 3. What is a stepper motor?  What is an example of an application that might use a stepper motor?
  A stepper motor can do a small amount of work when it receives a signal to do so – then it stops. We might use a stepper motor to control an automatic door. We would need to keep sending the stepper motor signals until the door was fully open. Each signal would make the door open a small amount. Of course, many signals are sent in 1 second, so we get the impression that the door opens automatically.
• 4. What is an analog to digital converter used for?  Provide a concrete example to support your answer.
  Analog to digital converters are used where ever a peripheral generates analog input for a computer. The computer can only process data that is in digital form. The ADC converts from analog to digital. A temperature probe used for a science experiment might provide data that is to be displayed in graph form on a computer screen. The program that makes the graph processes a digital input signal to make the graph. The ADC converts the analog temperature data into the digital temperature data used for input by the computer.
• 5. When would you use a digital to analog converter?  Provide a concrete example to support your answer.
  The output peripheral attached to a computer may only accept an analog signal. For instance, when we connect to the internet we transmit information over the telephone line. The telephone line (old ones anyway) carry an analog signal and not digital. We must convert our digital signal to analog (with the DAC in our modem) so that transmission to our service provider can take place.
• 6. What is a sensor?  Provide a concrete example to support your answer.
  Sensors connect a computer to the outside world. The sensor that indicates temperature is used as input by the computer that controls the air conditioning system in our classroom.
• 7. What are the components of a control system?  Provide a concrete example to support your answer by making a labeled diagram or else label a digital image.
  
• 8. What is an actuator?  
  This is a motor that can be switched off or on by a signal. They are commonly used in control systems where equipment is switched on or off depending on feedback from sensors.
• 9. What is meant by the term process control?
  Commonly, this means that a computer (with sensors) is used to control an industrial process without the need for human intervention. There are many advantages for doing this: - the computer system can respond very quickly to changing conditions since sensors provide information many times per second. Quality of product will be higher than for an equivalent manual processing system.
• 10. List three advantages of automating process control.
  There are many advantages for doing this: - (i) the computer system can respond very quickly to changing conditions since sensors provide information many times per second. (ii) Quality of product will be higher than for an equivalent manual processing system. (iii) The cost of manufacturing will be lower since machines will generally outperform humans when it comes to carrying out simple manufacturing tasks.
• 11. What is data logging?  Provide a concrete example to support your answer.
  Data logging is a technique used to gather information that can be used for testing a computer model. For instance, we could construct a model of an intersection and then verify the validity of the model by matching model output with the data acquired by data logging.
• 12. How could data logging be useful if you are going to make a computer model?
  Data logging is used to verify that a model is good (or otherwise).
• 13. What are the components required for data logging
  A sensor is required to take measurements. Some means of storing the sensor information needs to be used. This might mean using a control interface that is connected to a small transmitter that can send signals to a computer where data is stored in a hard drive.
• 14. Draw a diagram of a data logging system that you have designed to count the number of cars going into and out of the school at lunchtime.