The term “data logging" describes the measurement, collection and storage of information from sensors over a period of time Ch 5 & 23 Monitoring & Measurement

 You 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! Sensors Processing… Next???

 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.

In 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

 Controlling a chemical process  Controlling a nuclear reactor  Controlling a greenhouse environment  Controlling a central heating system  Controlling a set of traffic lights

 Monitoring a patient’s vital signs in hospital  Monitoring a scientific experiment in a lab  A burglar alarm system  Environmental monitoring (eg oxygen levels in a river)

 Analogue 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.

 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

 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.

 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.

SensorWhat it detects Temperature LightLight / dark PressurePressure (e.g. someone standing on it) MoistureDampness / dryness Water-levelHow full / empty a container is MovementMovement nearby ProximityHow close / far something is Switch or button If something is touching / pressing it

 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

 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

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

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, Light Humidity 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

 Manual data logging (monitoring)  A science experiment where you record data once a minute  Automated data logging (monitoring)  Example: a weather station which operates 24 hours a day, 7 days a week  Remote data logging (monitoring)  Example: a sensor inside a volcano to detect temperature changes

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.

 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

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