The term “data logging" describes the measurement, collection and storage of information from sensors over a period of time

Ch 5 & 23

Monitoring & Measurement

ObjectivesYou should have an understanding of

a range of ICT applications in everyday life and be aware of the impact of ICT in terms of measurement applications such as Scientific experiments Electronic timing Environmental monitoring

In both of these applications, sensors are used to send data to a computer where it is processed.

It’s what happens next where the differences occur!

Monitoring Vs Control 1Sensors

Processing…

Next???

Monitoring Vs Control 2 In Control applications, the computer

reviews data from the sensors against the data – parameters – stored in its memory

If the values are outside the given range, the computer takes action to try and get the values back within acceptable limits.

It does this by sending signals to devices controlling the processes – the actuators.

Monitoring Vs Control 3In monitoring, the computer simply

reviews the data (by comparing it to the data stored in its memory) and then

It updates its files It may give a warning signal…But it doesn’t make any changes

to the process

Examples of ControlControlling a chemical processControlling a nuclear reactorControlling a greenhouse

environmentControlling a central heating systemControlling a set of traffic lights

Examples of Monitoring

Monitoring a patient’s vital signs in hospital

Monitoring a scientific experiment in a lab

A burglar alarm systemEnvironmental monitoring (eg

oxygen levels in a river)

ADCs and DACsAnalogue data from sensors needs to

be converted into digital data so that the computer can understand and process the data from the sensors.

If the computer sends signals to motors, valves etc, then this data must be converted back to analogue using a DAC.

What do you need? The basic equipment for computer-

based measurement consists of Sensors, A data-logger A computer.

Normally, the sensors are plugged into the data-logger circuit box which in turn is connected to the computer.

Optionally, a printer is also useful for printing out graphs on paper

Sensors: A normal PC has no way of knowing what is

happening in the real world around it. It doesn’t know if it is light or dark, hot or cold, quiet or noisy. How do we know what is happening around us? We use our eyes, our ears, our mouth, our nose and our skin - our senses.

A normal PC has no senses, but we can give it some: We can connect sensors to it.

A sensor is a device that converts a real-world property (e.g. temperature) into data that a computer can process.

What do sensors do? A sensor measures a specific property data and

sends a signal to the computer. Usually this is an analogue signal so it needs to be converted into digital data for the computer to process. This is done using by an Analogue-to-Digital Converter (ADC).

Sensors are used extensively in monitoring / measuring / data logging systems, and also in computer control systems.

Examples of sensors

Sensor

What it detects

Temperature

Temperature

Light Light / dark Pressure Pressure (e.g. someone

standing on it) Moisture Dampness / dryness Water-level

How full / empty a container is

Movement

Movement nearby

Proximity How close / far something isSwitch or button

If something is touching / pressing it

Sensors The purpose of the sensor is to convert a

physical quantity into an electrical signal which can be translated by the computer into numerical values and graphical images.

A wide variety of sensors are now available. Temperature, light intensity, sound level, relative humidity, pH, pulse (heart rate), breathing, wind speed, and many more

Where is Computer Measurement Used?

Anywhere that data needs to be gathered regularly, a computerized data-logging system can be used.

Many experiments can be set-up and left to run with a data-logging system measuring things like the temperature of a liquid, acidity/alkalinity etc

Example 1: Scientific Experiments

Often these are placed in very remote areas to collect data about rainfall, temperature, wind-speed, wind-direction, etc.

Massive amounts of data need to be gathered all day, every day. This data can then be used by weather forecasters to help predict the weather over the coming days.

Example 2: Weather Stations

Scientists are very concerned about the effect that humans are having on the environment.

Computer-based data-logging is often used to help gather evidence of these effects: the level of water in

a dam, the speed of water

flowing down a river, the amount of

pollution in the air, etc.

Example 3: Environmental Monitoring

Environmental Monitoring: an example

Measuring oxygen levels in a river Sensors read data from the river Data is converted into digital using an

ADC Computer stores the received data Oxygen levels/acidity levels/pollution

levels are compared to historic data stored in the memory

Either: Data is transferred to a CD/DVD/memory stick

and taken away for analysis OR computer is connected to mobile phone

network and transmits the data automatically to the monitoring station

1. Sensors read key vital signs: Pulse/heart rate Temperature Blood pressure Respiration Oxygenation etc

2. Data from the sensors is converted using an ADC

Example 6: A Hospital patient

A Hospital patient

3. Data is stored in the computer’s memory

4. Computer compares the data from the sensors with the values stored in its memory

5. Results are output on a screen in the form of graphs, digital read-outs, printouts (usually using a plotter)

6. Alarm is activated if data is outside acceptable parameters

Sensors used: Humidity; moisture; temperature; pH,

LightHumidity sensor: Sends signal to an ADC which sends the

digital signal to the computer Computer compares the input with stored

values Decides what action needs to be taken If humidity is too high, computer sends

signal to a DAC to operate the motors to open the window

If humidity is too low, it sends a signal to open valves to spray water

Example 5: A Greenhouse Environment

Some chemical processes need precise conditions – eg temperature >70 and pH < 3.5

Temp & pH sensors read data from process

Data converted to digital using ADC Computer compares data with

stored limits Signals are sent as appropriate to

DACs and then to actuators

Example 6: A Chemical process

There are different ways of data loggingManual data logging

(monitoring) A science experiment where you record

data once a minuteAutomated data logging

(monitoring) Example: a weather station which

operates 24 hours a day, 7 days a weekRemote data logging

(monitoring) Example: a sensor inside a volcano to

detect temperature changes

The common functions of a data-logging program

1. Take readings from the sensors at regular intervals. It is possible to take many readings at time intervals ranging from a few microseconds to hours or even days.

2. Present the data in a suitable form of display on the screen. This could take the form of tables of numerical values, large digits, bar charts or most commonly as conventional graphs.

3. Print the data table or graph on paper using a printer connected to the computer.

4. Store the data on a computer disc for future use.

Why Use Computers to Measure Things?

Computers do not need to take breaks - they can log data all day, every day, without stopping

Response time if a parameter is out of range is faster

Computers take much more accurate readings than humans can

If a process is dangerous, it is better to monitor it or control it from a distance

Computers can take data readings more frequently (1000’s of times a second if necessary)

Computers don’t forget to take readings!

Since the logged data is already in a computer, the data can be analysed more quickly and easily (graphs drawn instantly, etc.)

Warnings can be given very quickly (eg buzzers/sirens)

Data logging systems can operate in difficult environments (e.g. in the Arctic, or on top of a mountain)

People are free to do other more useful tasks (rather than watching a thermometer)

No risks to humans eg falling in to rivers

Examples of live data from data logging

http://www.chimet.co.uk/ Click on more details to see what data is recorded

http://www.isleofwightweather.co.uk/station/Current_Vantage_Pro_Plus.htm Keep the page open and see if anything changes