8.data logging

8/12/2019 8.Data Logging

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Data Logging



Data logging is the use of sensors to measure and

record data automatically at regular intervals.

Sensors detect physical quantities and convert them

into electrical signals. These signals are sent to an interface box.

Sensors usually produce analogue signals, whichneed to be converted into digital signals by an analogue-to-digital converter (ADC) so that they canbe processed by a computer. The ADC is inside the

interface box.

Data Logging



Data logging is used where large amounts of data

are required over long or short periods of time.

As the measurements are taken automatically bysensors, data logging is often used where it wouldbe dangerous for a human to take measurements,

e.g.

Seismic activity (vibrations) near a volcano

Radioactivity inside a nuclear power station

The temperature inside a kiln

The digital data is then sent to a data logger, where

it is stored. At regular intervals, the data loggersends a batch of data to a computer to be analysed using formulas and charts.

Data Logging



Data logging can also be used where it would be

tedious and expensive for a human to take thereadings, e.g. recording the heart rate, and bloodpressure of a patient lying in a hospital bed…

Data Logging



Remote data logging is where the data logger sends

the data to a distant place to be recorded and stored.

Remote logging is used where the

equipment mightbe in danger ofbeing destroyed,or it would be

difficult ordangerous for aperson to retrievethe data fromthe site.

Remote Data Logging



Examples:

Monitoring the gas produced by a volcano

Remote Data Logging



Examples:

Checking the movement and stress atan earthquake fault line

Remote Data Logging



Examples:

Measuring the flow of lava

Remote Data Logging



The measurements are taken over a period of time,

called the logging period.

The choice of logging period depends on what isbeing measured, the purpose of the data logging,and how much data is required.

For an experiment in which the temperature ofwater is recorded as it cools, the logging periodcould be about an hour (the time it takes for the

water to completely cool).

For the monitoring of seismic waves (vibrations inthe Earth) near a volcano, the logging period mightbe unending, as scientists permanently record

volcanic activity in order to predict eruptions.

Logging Period



The time between measurements is called the

logging interval.

The choice of logging interval depends on whatquantity is being measured, the purpose of the

data logging, and how much data is required.

If you are measuring radiation emitted from agalaxy a long way away, you might only require

daily measurements.

If you are measuring the energy released from anexplosion, you might want a logging interval of a

fraction of a second.

Logging Interval



When setting up a data logging experiment, you

need to know how many readings to expect from thedata logging.

The formula is:

Number of Readings = Logging Period

Logging Interval

Number of Readings



Example: The electrical energy in a storm was

measured every 5 seconds for a period of 2 hours.How many readings were taken?

Number of Readings = Logging Period

Logging Interval

7200

5=

Logging Period = 2 hoursLogging Period = 2 x 60 x 60 secsLogging Period = 7200 secs

1440=

Logging Interval = 5 secs

Number of Readings



Data logging is much cheaper than using a human to

take measurements.

Advantages of Data Logging

There is no chance of any human error, so datalogging is much more accurate than human

measurement, as long as the sensors have beencalibrated properly.

Data logging can take place 24 hours a day, 7 days aweek. Sensors don’t need a break.

Data logging can take place in inhospitable anddangerous places, where it would not be possible fora human to be, e.g. on Mars, or around the rim of a

volcano.



Sensors can break, in which case data will not be

captured and recorded until it is replaced or fixed.

Disadvantages of Data Logging

Some sensors can be expensive.

The equipment may take a while to set up.

Sensors must be calibrated properly, otherwise the

data they produce will be invalid.



Keyword Activity 1

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Keyword Activity 2

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Quiz



After viewing this presentation, you should…

Know that data logging is the use of sensors tomeasure and record data automatically at regularintervals.

Be able to give practical examples of data logging.

Know about the advantages and disadvantages ofdata logging.

Understand logging period and logging interval, andhow these are chosen.

Know about remote data logging and why it is used.

Objectives

Be able to calculate the number of readings.

Be able to explain the role of the sensor, ADC,

interface box, data logger and computer.

8.data logging

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