Monitoring and Control Systems

• Monitoring system

  Involves the use of a computer or microprocessor based device to monitor or measure physical variables over a period of time
• Sensors

  Sensors are devices that can detect and measure physical or chemical properties and convert them into electrical signals
• Types of sensors

  Light/UV

  Temperature

  Pressure

  Humidity/moisture

  Sound

  Infrared
• Light/UV sensor

  measure amount of light

  • used in weather stations to measure the amount of sunshine
• Temperature sensors

  measures ambient temperature at weather stations

  • measure temperature changes using the expansion or contraction of materials
• Pressure sensors

  converts the force applied to its surface to generate electrical energy which is then converted into values to represent applied pressure

  • used to measure atmospheric pressure in weather stations
• Humidity/moisture sensors

  Combination of moisture and temperature

  • measures absolute and relative humidity
  • humidity sensors used at weather stations
  • moisture sensors are also used when monitoring soil quality
• Sound sensors

  Convert sound waves into voltages or electrical signals which are converted by the computer into values to represent sound

  • used in environmental monitoring systems to measure noise pollution
• Infrared sensors

  All bodies possess thermal energy - emit infrared radiation converted to electrical signals

  • used in environmental monitoring e.g. the Earth’s surface temperature can be monitored by satellites
• Monitoring Water Pollution

  Compare the readings with those that would normally be expected

  • requires the lowering of the one set of sensors into river or lake

  Relates to industrial pollution

  • involved inserting two sets of sensors between suspected site of pollution
• Environmental Monitoring

  Collections of data relating to our environment

  • monitoring sound in cities, in addition to other pollution produced by motor vehicles
  • monitoring soil quality
• Control Technologies

  Uses microprocessors or computers to control certain physical variables

  • real-time processing system processes data as soon as has been input

  In control systems the output affects the input
• Electromagnetic Field Sensors

  Measures change in the Earth’s natural magnetic field caused by the presence of a ferromagnetic object
• Electromagnetic Field sensors Use

  Used in some automated car parking systems to help drivers park their car
• Ultrasonic Sensors

  made up of device that sends out sound waves with a high frequency and a sensor that receives the sound waves

  • used in car parking systems
• Proximity Sensor

  Composed of different sensors which send a signal to be received back
• Touch Sensors

  Used for measuring fluid levels

  • capacitive touch sensor - measures capacitance between two conductors separated by an insulating plate

  When fluid is touching the sensor, it detects the level that it is
• Actuators

  Controls a device and produces and output

  • a device that turns an electrical signal from a microprocessor into movement
• Advantages of Actuators

  They can be programmed to execute several different tasks

  They are small in size so can be easily built into different technologies

  They are relatively fast at moving data between different memory locations
• Disadvantages of Actuators

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

  They are only small in size and can over heat if too much demand is placed on them
• Sensor Data Acquisition And Processing

  Sensors generate analogue signals - which need to be converted into digital signals for processing by computers or micro controllers

  Analogue to digital converters are used to convert the continuous analogue signals into discrete digital values

  • Sensor data can be processed using algorithms and software to extract meaningful inform or trigger specific actions
• Advantages

  Accuracy

  • sensors are extremely accurate and cancel out any human error

  High performance

  • can work in any type of condition allowing them to be fast and efficient
• Disadvantages

  They can be affected by environmental changes and exposed to contamination

  Overtime as they’re being used they can wear out and deteriote overtime

  Difficult to program computers to interpret the results
• Calibration

  The process of configuring an instrument to provide a result for a sample within an acceptable range
• Importance of Calibration

  Accuracy and reliability

  • calibration corrects any deviations or errors in the measurement, ensuring the data generated is trustworthy

  Consistency and compatibility

  • establishes a common reference point or standard, allowing measurements from different sources to be interpreted consistently

  Quality assurance

  • helps identify and correct any potential errors or inaccuracies
• Methods of Calibration

  one-point calibration

  two-point calibration

  multipoint calibration
• One-point Calibration

  Adjustments made at one reference point which is chosen at or near the expected operating range of the instrument
• Two-Point Calibration

  Involves adjusting the instrument at two reference points

  • these reference points are chosen to cover a range

  The instrument’s response at those two points area compared with the known values and adjustments are made to ensure accuracy
• Multipoint Calibration

  involves calibrating the instrument at more than two reference points across its operating range

  • provides a more comprehensive assessment of the instrument’s accuracy and can detect nonlinear or other deviations from ideal behavior

  Often necessary for instruments that require high accuracy over a broad range of measurements or when the instruments response is nonlinear
• One point calibration 


  One point calibration is appropriate for sensors used to measure a value that is constant

  The offset only is calculated then the offset is then added to every subsequent reading
• Two point calibration 


  Sensitivity needs to be included not just an offset

  Used where there is a linear relationship between the two readings

  The slope of the line connecting the two readings is compared with the slope of the line of the pre-calibrated sensor