Data logging & data acquisition
The terms data logging and data acquisition are often used interchangeably. However, in a historical context they are quite different. A data logger is a data acquisition system, but a data acquisition system is not necessarily a data logger.
Data loggers typically have slower sample rates. A maximum sample rate of 1 Hz may be considered to be very fast for a data logger, yet very slow for a typical data acquisition system. Data loggers are implicitly stand-alone devices, while typical data acquisition system must remain tethered to a computer to acquire data. This stand-alone aspect of data loggers implies on-board memory that is used to store acquired data. Sometimes this memory is very large to accommodate many days, or even months, of unattended recording. This memory may be battery-backed static random access memory, flash memory or EEPROM. Given the extended recording times of data loggers, they typically feature a time- and date-stamping mechanism to ensure that each recorded data value is associated with a date and time of acquisition. As such, data loggers typically employ built-in real-time clocks whose published drift can be an important consideration when choosing between data loggers. Data loggers range from simple single-channel input to complex multi-channel instruments. Typically, the simpler the device the less programming flexibility. Some more sophisticated instruments allow for cross-channel computations and alarms based on predetermined conditions. The newest of data loggers can serve web pages, allowing numerous people to monitor a system remotely.
The unattended and remote nature of many data logger applications implies the need in some applications to operate from a DC power source, such as a battery. Solar power may be used to supplement these power sources. These constraints have generally led the data logger industry to ensure that the devices they market are extremely power efficient relative to computers. In many cases they are required to operate in harsh environmental conditions where computers will not function reliably. This unattended nature also dictates that data loggers must be extremely reliable. Since they may operate for long periods non-stop with little or no human supervision, and may be installed in harsh or remote locations, it is imperative that so long as they have power, they will not fail to log data for any reason. Manufacturers go to great length to ensure that the devices can be depended on in these applications. As such data loggers are almost completely immune to the problems that might affect a general-purpose computer in the same application, such as program crashes and the instability of some operating systems.
Applications of data logging include:
Through process monitoring of temperature for QA purposes in the paint and powder coating industries
Monitoring cooking, pasteurization, chilling and freezing temperature within the food industry
Short and long term data capture of a variety of physical parameters in scientific and industrial research projects
Monitoring in buildings
Monitoring temperature and humidity in public and commercial buildings such as museums, galleries, stately homes, warehouses, etc.
Monitoring various physical parameters during vehicle testing
Monitoring river flow and discharge levels in the water and sewage treatment industries
Monitoring cure temperature of poured concrete structures
Monitoring temperature, humidity, wind speed and direction, solar power and other environmental parameters in ecological studies