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Data logger
Friday, 01 September 2006

Data logging is the recording of data values generated by, and concurrent to, the execution of some generating process. The efficient storage and retrieval of multi-channel data communications are critically important in many modern business and government applications. For example, financial institutions record instructions from clients as a protection against fraud and as evidence in legal proceedings about the content of telephone conversations; public safety agencies record emergency calls for event reconstruction and future investigations; commercial entities monitor transactions over the phone to evaluate salespersons' efficiency, to ensure customer satisfaction and to develop training programs. In many industrial applications, a variety of data reading must be recorded, such as the temperature reading, pressure value, flow rate or electric power reading, etc. The ability to monitor, record and analyze process and equipment behavior is frequently necessary in many process, manufacturing, research, and utility applications. Logging is the process of recording system events so that those actions can be reviewed later. In data logging, a data gathering instrument monitors a process or situation and gathers and stores information about the process or situation for later analysis or archiving. Logging is used in database management systems to record updates to the database to facilitate recovery in the case of a system crash or media failure. It is also used to record the previous value of a record before an update so that the change can be undone. A data logger may generally be described as a recording device for creating a time-sequence history of events. A data logger is used for logging or accumulating data received from a data source. Data logging is now widely used in computer simulation to provide a record of the activity of the simulated system for subsequent processing and analysis.

Generally speaking, data loggers are devices that record measurements obtained from electronic sensors that sense physical properties such as temperature, pressure, electrical current and voltage among others. A data logger is made up of a digital processor operationally connected to a non-volatile memory bank for storing measurements obtained from electronic sensors in communication with the data logger. Typically, data loggers include probes or sensors which measure product environmental parameters and are connected to the data logger. In addition, the body of the data logger itself may include sensors to detect conditions, such as humidity, which do not require a probe. Data loggers are often protected from mechanical abuse during usage to ensure accurate recording of environmental data. After recording such data, data loggers are often required to be repackaged and mailed to a central site for downloading or reprocessing. Most of the data loggers are capable of downloading such data through a mechanical multi-pin connector an infrared or RF transmitter normally found in a PC system to permit processing through a data base. Other major components include at least one digital communication port for communicating with an external user interface device such as a personal computer (PC) or personal digital assistant (PDA) and a real-time clock for keeping track of time as well as calendar dates. Optional components can include sensor interfaces such as analog-to-digital converters and event counters used to convert analog signals and discrete events into digital form for storage into the non-volatile memory bank. The data recorded by the data logger is generally stored in some type of data memory within the data logger. In many instances, a non-volatile memory is used to ensure that the data stored in the data logger is saved even after the battery is removed or the data logger is damaged. An increasing number of commercially available data loggers have in-circuit firmware programming capability. This capability allows a user to erase a data logger's current firmware and upload new firmware. In general, a typical data logger is battery powered and includes a sensor, microprocessor, memory, and computer interface. The sensor measures some parameter and generates a signal indicating the measurement. Data is derived from the signal, and the microprocessor stores the data in the memory. The microprocessor may time stamp the data. Subsequently, the data is transferred from the memory to a computer through the computer interface. The computer then analyzes the data.

A data acquisition system generally receive an external input from some type of sensing device, condition and/or convert the input to a format suitable for transmission, and transmit it to another piece of equipment usually a monitor or controller, which may be a computer. The external input is generally an analog signal, although digital signals, frequently on-off switching, pulse-width modulation, or serial data protocols, are also involved. The inputs, though, come in many forms with many different characteristics. Data collection involves several steps, including selection of monitoring equipment, assembly of instrumentation, programming, field installation, maintenance, data recording, data downloading and disassembly of field installation upon project completion. Traditional data logging methods operate in a linear fashion by generating a first record of data, writing the first record of data to disk, generating a second record of data, writing the second record of data to disk, and so on. This approach does not optimize the writing of a large amount of data to disk, such as the voluminous data stream generated when modeling the application. Development of digital technique is making it possible to store mass of media data for its applications without degradation. In particular, with a tendency toward lower cost of processors and recording devices, digital recording apparatuses employing hard discs to the recording devices are being offered recently to the public. In these digital recording apparatuses, not only hardware functions but also what is made possible by making the best use of the hardware functions is of importance, and software is therefore being recognized to be more significant functions. Data loggers are typically operated in one of two data collecting modes. Numerous other operating modes and features are incorporated into modern data loggers. The most prevalent mode is time-based mode. In this mode, a data logger is scheduled to obtain data readings from a sensor or number of sensors at a given time interval. Another operating mode for data loggers is event driven. In an event driven operating mode, a data logger only records data when triggered by an external event.

Data loggers are employed in many industries to ascertain environmental parameters. A data logger is basically an electronic device that records measurements such as temperature, relative humidity, light intensity, wind direction, wind speed, visibility, precipitation, depth, current, voltage, pulse, events, etc. at regular time intervals. Other environmental parameters such as stream flow, water quality, topography, and terrestrial habitat can also be measured using the data logger. Data loggers are used in shipping and storage containers to measure and record environmental conditions such as temperature, humidity, pressure, and vibration. Probably the most common use of data loggers is temperature recording, with the aid of thermistors, thermocouples, or other temperature measuring devices. In an industrial chemical process, reaction temperatures may be recorded by a data logger continuously for quality assurance purposes to determine whether the temperatures stayed within predetermined bounds during the reaction. Data logging can also occur during medical treatment and procedures. For example, emergency medical technicians delivering emergency care may use defibrillators to deliver electrical shocks to a patient's heart. Event data regarding the patient's physiological condition may be logged to provide information to later caregivers about the patient and about the care the patient received. Data loggers are used in the field of weather observation to obtain time records of wind speed and direction, relative humidity, barometric pressure, or rainfall, and in the field of geological surveying for detecting earth movement. For atmospheric measurement, data loggers have been used to measure atmospheric parameters, such as temperature, pressure, humidity, wind, and solar radiation. Tethered balloons are used to transport data loggers to altitudes where measurements are taken. Data loggers are also involved in field studies, transportation monitoring, HVAC tests, quality studies, troubleshooting, general research, and the like. Thus, it is easy to understand why data loggers are commonly used in a wide variety of applications.