monitoring, measurement and control technology

Monitoring, measurement and control technology


Definition of data logging

Data logging – collecting data automatically from sensors over a certain period of time


Sensors

• Used to detect and measure physical quantities

• Sensors include temperature, light, humidity, sound, pressure, etc.


Sensors• Heat – investigating the cooling of a hot drink,

control a heating system, fire alarms, cookers.• Light – Used to automatically come on when it is

dark, used in plant growth environments, burglar alarms

• Sound - Decibel readers in noise disputes, alarms.• Pressure – air pressure, barometric, depth of liquid• Humidity – measure moisture in the air• Passive Infrared Sensors (PIRs), detect movement,

alarms


Data logging

Important quantities that need to be set:• Logging period – total time over which

all the readings will be collected• Logging rate/interval – how often the

readings are taken• Location of sensors


How data logging works

• Data is collected from the sensors• It can be sent to the computer using wires

or wirelessly• The computer processes the data (i.e.,

works out maximums, minimums, averages, etc.)

• The computer can also process the data by producing graphs and charts


The advantages of data logging


The disadvantages of data logging


Controlling devices

• Actuators – mechanism that turns a device on or off, or moved, e.g. a motor.

• Touch sensors – smart phones, PCs• Sequence of instructions to control devices – See

Lightbot.


Main components of a control system

• Sensors• Computer / processor• Output devices


Main components of a control system

• Non feedback control systems.– Works regardless of feedback, e.g. does not receive any

feedback as to the control sequence has been implemented.

• Simple control systems– The computer decides whether to switch an output device

on or off depending on the data it receives from a sensor– Examples include: Security lights, Automatic doors, Burglar

alarms


Output devices controlled by control systems

• Actuators – these are devices such as motors

• Stepper motors – these turn in a series of small steps that you can control

• Bells/sirens – for alarms/warning sounds• Heaters/coolers – for heating/air

conditioning systems


Control Feedback loop

• Feedback makes the control system more intelligent and useful.

• Read the example of a Control-Feedback loop on page 164

INPUTINPUT PROCESSPROCESS OUTPUTOUTPUT AA

monitoring, measurement and control technology

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