Source Documents

A source document is a document in which data is collected for entry into a computer system.

Examples of source documents include:

Medical records Lab reports Subject diaries X-rays ECG printouts

Types of Source Documents

A turnaround document is a document that has been output from a computer, some extra information added to it, and then returned to become an input document. For example, the document on which electricity meter readings are recorded is then used as a source of input for preparing electricity bills.

A machine readable document is one designed and printed in such a manner as to allow the data on it to be read by a computer - for example a barcode.

Human-readable refers to a representation of information that can be naturally read by humans, as compared to data designed for reading by computers. The numerals that commonly accompany a UPC barcode are a human-readable form of the information present in the barcode. In the case of barcodes used in stores, laws frequently mandate that a human-readable price be displayed with the merchandise, rather than relying solely on the machine-readable barcode and price disclosure only at the point of sale.

ISBN-13 represented as EAN-13 bar code showing both machine-readable and human-readable data.

Data Logging

Data logging is the automatic collection of data over a certain period of time. The logging period and interval can be altered depending on what is being measured.

Logging period is the time period over which the measurements take place.

Logging interval is the frequency with which the individual readings are taken (i.e. per second, per minute, per hour).

Data logging systems may use a variety of sensors to receive input data.

SensorsSensors are used to detect various physical quantities, such as temperature, pressure, sound, light. The sensors are connected to a computer through an interface and with special software the readings are displayed on the computer screen.

Types of Sensors: Mercury tilt switch

o A blob of mercury moves to close a circuit when a tilt is detected Light sensor

o Detects high or low light levelso Used to operate street lightso Used in barcode readers

Push switcho Can be used to switch on a light when pressure is removed from the push

switcho Used in car doors and fridge doors to turn on a light when the door is

opened Temperature sensor

o Responds to increases and decreases in temperatureo Used in central heating and air-conditioning systems to keep room

temperature constant Sound sensor

o Measures the level of soundo Used by environmental health officers to determine if sound levels are

unsafe for people Proximity sensor

o Detects if distance is placed between the two halves of the sensoro Used in some security systems e.g. to sound an alarm if a window is

opened Pressure sensor

o Detects the presence of an object by the pressure exerted on ito Used in traffic control systems to record the volume of traffic passing

through an intersection, so that traffic lights can be regulated

Advantages of data logging: It can be used for fast events that would happen too quickly for manual readings It can be used for slow events where manual recording would be tedious Since readings are taken automatically, they are accurate and free from human

error Readings are taken at exactly the right time every time