3 Monitoring and control

• A monitoring system is a system that observes and often records the activities in a process
• A control system is a system that manages or regulates a process by physically changing aspects of the system depending on collected data
• A sensor is an input device that collects data from the surrounding physical environment
• Advantages of a sensor

  data can be repeatedly collected 24 hours a day so a human can rest

  data can be collected in dangerous and harmful environments so lives of humans are not endangered
• Types of sensors

  light sensors

  temperature sensors

  pressure sensors

  moisture and humidity

  sound sensor

  touch sensor

  proximity sensor

  infrared sensor

  motion sensor
• Light sensors measure the level of light

  They are used in external security lights
• Temperature sensors detect and measure hotness and coolness

  They are used in central heating systems
• Pressure sensor senses and measures pressure

  They are used in burglar alarms and automatic doors
• Moisture and humidity sensors measure the water vapor in the air

  They are used in swimming pools and greenhouses
• Sound sensor detects the intensity of the sound

  They are used in microphones
• Touch sensors capture and record physical touch

  They are used in mobile devices
• Calibration is the process of testing and modifying a device to make sure that it is taking the correct readings
• One point calibration

  simplest method of calibration

  can be used to correct an offset calibration curve

  this is because the sensor is reading partly correct but it is consistently too high or too low
• One point calibration method

  take a reading with a sensor

  compare the reading with a device measuring at the ideal standard

  subtract the reading from the reference to get the offset

  add the offset to every reading to get the calibrated value
• Two point calibration

  can be used to correct data suffering both offset and sensitivity

  can be more accurate than one point calibration
• Two point calibration method

  take two different readings with a sensor

  compare readings to readings from a device measuring at the ideal standard

  calculate the range value for the sensor readings then the ideal standard by subtracting low reading from high reading

  use a formula to calculate the correct value for each reading
• Multipoint calibration

  similar to other calibration methods but is performed using at least three different readings

  this further increases the accuracy of calibration and can help calibrate sensors that would produce readings that do not naturally form a linear line
• Offset means that the readings are higher or lower than the ideal reference
• Sensitivity means that the readings change over a range at a different rate than the ideal reference
• Linearity means that the readings are directly proportional to the ideal reference
• A monitoring system is designed to collect the data and then store it so that it can be used at a later stage
• The main technology used in monitoring systems are sensors. Other technologies used are storage devices to store the data collected and graphing software could also be used to create a visual representation of the data to make it easier to interpret
• A control system is designed to collect data and then send this to a computer system so it can be analysed
• A microprocessor is an integrated circuit that is used in monitoring and control systems
• Advantage of microprocessor

  they can be programmed to execute several different tasks

  small in size so can be easily built into different technologies

  relatively fast at moving data between different memory locations
• Disadvantage of microprocessor

  there is a limit on the size of data they are able to handle

  small in size so can overheat if too much demand is placed on them
• An actuator is a type of motor that is used to move and operate another mechanism or device
• Advantage of actuator

  hydraulic and electric actuators are fairly quiet

  moderate-high speed

  pneumatic actuators cost is relatively low
• Disadvantage of actuator

  pneumatic actuators can be quite noisy

  fluid leaks in hydraulic actuators

  hydraulic and electric actuators cost is relatively high