6. Monitoring and Control Systems

All Past Paper Questions: https://docs.google.com/document/d/1Ms7cSAQ7I4NGc3m3egiCirOHodjetUsTdt2eyuenYjI/edit?usp=sharing

Analongue-Digital

• Microporcessors/computers cannot directly process analogue data

ADC

Processor

DAC

Monitoring

• Computers

  • never forget to take reading at regular interval
  • more accurate
  • several variables can be measures simultaneously
  • results processed automatically
  • can take readings from dangerous areas (using sensors)
  • sensors will wear off over time

• Humans

  • needed to place sensors
  • needed to interpret results
  • maintain broken senors
  • have to program the computers
  • have to plan where to place the sensors

Uses

• Weather Stations

  • sensors are used to feed data back to computer
    • sesnors gather: humidity, temperature, rainfall, etc...
  • analgue data is converted to digital form for processing using ADC
  • compurter stores readings in a table
    • ready to be processed
    • plots graphs automatically
  • calculates minimum and maximum temperature
  • outputs graphs on screen

• CCTV monitoring

  • advantages
    • will monitor constantly
    • so, will keep criminals away
    • makes employees less likely to steal
    • if a crime occurs, CCTV fotage can be used as evidence
    • if conflict among employees, boss can decide what actions to take by watching footage
    • disputes with customer and employee, can share blame with this footage
    • increases productivity, as they know that they are being watched
    • can monitor who violates rules and policies
      • and take disciplinary action
    • software can also be used to track employee activity
  • disadvantages
    • not able to display every bit of an area
    • invasion of privacy
    • employees may feel uncomfortable
      • and mistrust employer
      • causing some workers to leave
      • and creating increased turnover of employees
    • hackers can get into the system
      • and see everything
      • and delete footage of crimes commited
    • hardware is expensive to purchase

• Monitor Workplace

  • advantages (emloyer)
    • software expensive to purcahse
    • system expensive to set up
    • can lend to lawsuits for piracy infringement
    • mistrusting employees creates trust issues
  • advantages (employee)
    • video monitoring gaurantees their security
    • provides detailed view of what employees are doing
      • weather they are following orders, etc...
  • disadvantages (employee)
    • allows employers to monitor without employees knowing
    • but, some employers do not notify employees
      • they secretly monitor (so, bad)

• Monitoring Pollution

  • measure (using sensors):
    • temperature, tubidity, pH, O2, CO2, nitrite, nitrate
  • place sensors at upstream and downstream in factory
  • temperature/light sensor connected to computer
  • ADC converts analogue data to digital data
  • so the computer can understand readings
  • readings are compared with pre-set limits
  • different results are printed out
    • eg: Max, Min and Avg temperature, etc...
  • graphs automatically produces
  • computer stores in a table, ready for further processing

• How to monitor data?

  • sensors are used to gather the particular physical variables
  • sensors feedback data computer
  • analgue data is converted to digital data by ADC
  • computer stores readings
  • computer compares to pre-set values
  • computer performes calculations and processing
  • calculates this at set intervals
  • plots graphs of values against normal values
  • computer produces graphs automatically

Control Systems

• output affects the input

• Monitoring vs Control Systems

  • similarities
    • both involve the use of sensors
    • both do not require human output
    • both require ADC
  • differences
    • in control systems, output affects the inputs
    • acts in real-time
    • uses output devices like acturators

• Real-Time processing

  • general
    • responds to processed inputs instantaneously
    • has to deal with inputs continuously
      • eg: air conditioning system
    • found in systems that use sensors
    • user interface uses specialist input devices
    • to provide data input
      • eg: touch screen, remote control
    • usually deals with small amounts of data
    • output affects the input
  • explanation (air conditioning)
    • an information system must process inputs (instaneously)
      • quickly enough
      • to be able to control an output properly
    • have to be programmed carrefully
      • so, no input events are missed
    • controlling car park barrier with providing input using light sensors
    • should be effective with very large volumes of data
      • but control systems has only small amounts of data to deal with
    • must react to approach immediately
    • system must react to input immediately
    • requires complex & expensive operating system
    • real-time systems are not easy to develop

Uses

• car park barrier

  • answer 1
    • (with micro-controllers)
    • pressure sensor / induction loop in driveway
    • sends signal to processor
    • ADC converts analogue signal to digital signal for microprocessor to process
    • microprocessor compares input with pre-set value
    • if its greater,
      • send signal to actuator
      • which raises the barrier
    • light sensor detects break in laser
    • when beam of light resumeds,
      • actuators activated again
      • lowring the barrier
  • answer 2 (detailed)
    • when car arrives
      • precence detected by induction loop
        • because electromagnetic loop is disturbed by metallic object
      • message sent to computer
      • computer sends signal to motor
      • motor raises the barrier
      • a light beam from one post passes across
      • to a light sensor in the other post
      • if microprocessor recieves signal
        • signal sent to motor to lower the barrier
      • else, barrier remains vertical
    • when car leaves
      • gues recieved ticket from reception
      • exit barrier asks for the ticket
      • computer compares ticket with acceptable tickets to check validity
      • if it matches
        • computer sends signal to motor
        • motor causes barrier to raise
        • a light beam from one post passes across
        • to a light sensor in the other post
        • if light sensor sends a signal
          • signal sent to motor
          • to lower the barrier
        • else
          • barrier remains vertical

• in burglar system

  • keypad to select areas
  • sensors for input
    • infra-ref sensors (to detect head)
    • sound sensors (to detect increased levels of sound)
    • pressure sensors (to detect increase in weight)
  • microprocessor compares input's reading with pre-set values
    • which is programmed in
    • to check if reading is above pre-set value
  • if not, sends instruction to actuator
  • actuator triggers alarm
  • a signal might also be sent to the police

• cooking a meal

  • start time is set with buttons
  • required temperature is set
  • length of cooking time is set with buttons
  • temperature is stores as pre-set values
  • microprocessor continuously checks start time against its internal clock
  • if start-time = internal clock time
    • microprocessor sends message to actuator
    • actuator switches on the heater (and fan)
  • else, take no action
  • temperature sensor reads temperature inside the oven
    • ADC converts anaolgue data from sensor to digital data
    • and sends temperature of microwave oven to computer
  • microprocessor continuously compares temperature of oven against preset value
  • if temperature is greater than pre-set temperature
    • microprocessor sends message to actuator
    • actuator switches off the heater
  • else,
    • microprocessor sends message to actuator
    • actuator switches on the heater
  • if the end time = internal clock
    • microprocessor sends message to actuator
    • actuator switches off the heater (and fan)

• in bussinesses

  • computer controlled production lines
    • increase unemployment
  • computer controlled printing presses
    • replace printing workers
  • IT technicians needed to maintain these infrastructure
  • number of new jobs are less than jobs lost

• in homes

  • smart home
    • ascpects of home are controlled from a computer system
    • devices in the home are connected
    • types of devices that can be controlled
      • lighting, heating, air-conditioning, television, kettle, plugs, etc..
    • controlled by issuing commands
      • or from routines / schedules
    • uses home network
    • uses internet access when outside the home
  • advantages
    • microcontrolled devices can be used to do small tasks, saving time
    • more secure
      • burglar alarms can be used
      • smart home appliances
    • smart fridges
      • analyze food constituents
      • can encourage a healthy life-style
    • can turn on remotely
    • can schedule
    • rather than controlling/setting-up the control devices
    • saving time
      • for greater social interaction
  • disadvantages
    • can lead to people becoming lazy
    • loss of household skills (due to use of microcontrolled devices)
    • expensive equipment
    • difficult to repair
    • subjectable to hackers
      • can spy
      • change systems for their advantages
        • disable alrarms to enable burglary

• traffic lights

  • fewer traffic jam than manually controlled
  • input devices
    • induction loop
      • when a vehicle goes over it
      • the computer will get a signal
    • sound sensor
      • kerb stones constantly feeding back to computer sound level
      • if noise above set value limit,
        • it means a vehicle has passed it
    • video camera
      • fixed above traffic lights
      • registers approaching vehicles
      • and sends to computer
    • push buttons
      • when predestrian presses a button
      • signal goes to computer
      • to register a pedestrian is waiting to cross
  • systems waits for a pre-set time
  • computer sends signal to actuator
    • to change traffic lights from green to red
    • to chnage pedestrian control light to safe
  • computer initiates count down for a pre-set time
  • and sends signal to actuator
    • to change traffic lights from red to green
    • to change predestrian control light to unsafe
  • outputs
    • display above pedestrian button
    • beeping sound
    • red/amber/green lights that drivers see
    • count down

• street light

  • more economical
  • turns on/off automatically

• Air Conditioning in stores

  • increases costs of store
  • so, prices to the customer

Input Devices

Characters

• MICR

  • magnetic ink character recognition
  • advantages
    • characters are readable even if document is overprinted
    • high security
      • since they are difficult to forge
    • error rate reading them is small
    • data entry is quicker than typing details
  • disadvnatages
    • more demanging printing process
    • has difficult-to-achieve standards
    • causes a slower print
    • readers are expensive to purchase
    • recognizes fronts written in specific format only
    • MICR printer catridges are much more expensive

• OCR

  • optical character recognition
  • advantages
    • faster than entering large amount of text
    • cheapter than paying someone to enter text
    • allows documents to be made editable
    • will have a sofcopy, incase of a conflict
    • can read all data
    • will read continuosly (and consistently)
      • unlike humans, who will get tired
    • in banks:
      • cheques can be processed after being deposited at ATMs
      • cheques can be processed after being sent by phone
  • disadvnatages
    • all documents should be checked manually and carefully
    • as its not 100% accurate
      • has errors:
        • 'm' instead of 'rn'
        • '0' instead of 'O'
    • less secure,
      • eg: in banks, checks are easier to forge
    • need expensive OCR equipment and software
    • difficult to detect human handwriting
      • whereas, humans can do it easily

• OMR

  • optical mark recognition
  • advantages
    • used in exams
    • easier for students to complete
    • essential candidate details can be pre-printed
    • faster to mark scripts
    • more accurate marking of scripts
    • statistics are more easily produced
  • disadvnatages
    • cannot express themselves easily
    • answers are not easily human readable
    • questions cannot be open ended
    • equipment is more expensive to purchase

Sensors

• Induction Loop
  • gets disturbed my metal objects (like vehicles)
  • can know how many vechicles are here
• Humidity Sensors
  • measure absolute and relative humidity
  • is like a combination of moisture and temperature sensor
  • used in weather stations
• Pressure Sensors
  • measure atmospheric pressure
• Temperature Sensors
  • measures ambient temperature
  • used in weather stations
• Light Sensors
  • measures light levels
  • used in weather stations to measure amount of sunshine
• Sound sensors
  • converts sound waves to digital signals
  • used in environmental monitoring systems
• Infra-red sensors
  • detects heat
  • living bodies (eg: humans) emit thermal energy
  • turns infra-red electromagnetic waves into an electrical signal
  • used in burglar systems
    • detects movement
    • beams can be setup among rooms
    • IR sensors detects when the beam is broken
• Ultrasonic senros
  • measures distance
  • detects sound
  • turns soud waves into electrical signals
  • used in automated car parking / reversing system
    • device in car sends out sound waves
    • they are reflected back
    • device calculates distance from an object
    • by measuring time between emission and reception
      • speed = distance / time
• Electro-magnetic field sensor
  • used when parking a car
    • measures change in magnetic field
    • caused by body of vehicle
    • are used at entrances to control barriers
    • used to detect number of parking spaces available
• Reed switch and tipping bucket
  • measures rainfall

Other

• Touch screens (sensors)
  • used for measuring fluid levels
  • like, cooling water
  • capacitive sensor measures capacitance between two conductors seperated by an insulated plate
  • one of the conductors is fluid
  • detects when the fluid is touching the conductor

Input Calibration

• importance
  • accuracy of sensors reduces over a period of time
    • due to constant use
  • regular calibration helps maintain accuracy of sensors
  • other devices may detriorate over time resulting in a need for recalibration

One Point

• easiest to carry out
• only one measurement point (reading) is taken
• sensors measure a value that is constant
• the offset only is calculated
  • offset then added to subsequent reading
• can only be used when measuring constant physical variables
  • so, has a limited use

Two Point

• 2 measurement (data) points (readings) are taken
• measure constantly changing variable
• sensitivity needs to be included not just as an offset
• used when there is a linear relationship between two readings
• gradient of line between two point is calculated
  • and compared with standard values range
• compensates for both offset errors and sensitivity errors
• a range of values are being monitored
  • so, more complex
• value of offset is calculated
  • by comparing to reference readings

Multi Point

• has non-linear, multi-point relationships
  • greater knowledge of maths is needed
  • so, most complex
• multiple points (measurements) of data are used
• detailed
  • uses many readings from sensor
  • readings taken at high value, middle value and low value
  • best used where readings form a curve
  • readings taken by check (previously) know readings
  • calibration cannot be carried out
    • by adding an offset value
    • by allowing for the slope
  • to calibrate the sensor
    • the algorithm needs to include 'curve fitting'
  • uses a formula to calculate the correction
  • uses a quadratic function, like: ax^2+bx+c
  • where
    • y reading
      • is the reading from standardized sensor
    • x value
      • is from the sensor needing calibration

Output

Actuator

• Purpose
  • provides output from a control system
  • mechanical part of control system
  • actuator controls/operates device
  • like, opening a valve
  • turns an electric signal (from a microprocessor) into physical action

Other

Expert Systems

• Knowledge Base

  • consists of a database of facts
  • inference engine
    • uses rules base to reason through symptoms
    • uses facts in knowledge base for reasoning
    • compares to symptoms to those in knowledge base
    • uses rules base of IF...THEN...
  • knowledge base editor enables knowledge engineer to edit rules

• Forward Chaining

  • inference engine uses this to search inference rules
  • until it finds one IF statement which is true
  • in here, the inference engine will use the 'THEN' part
    • to cause addition of new information
  • inference engines repeats this until a goal is reached
  • data entered determines which rules are selected and data used
    • this is called 'data-driven'