Portable data loggers come of age

Portable data loggers have developed rapidly over the past decade, especially as the requirement for "on-demand data" increases, says Signatrol MD Brian Turner.

Typically portable data loggers are used as secondary controls to check and validate processes and events, providing an essential data continuum in processing, storage and transportation environments.

In the past, data loggers have tended to be relatively bulky devices, which often needed to be powered via the mains supply or large battery packs, thus restricting their use to permanent or semi-permanent installations.

Significant developments in low power electronics and battery technology have enabled manufacturers to design smaller and smaller portable data loggers and as a result, their use is increasing significantly across a broad spectrum of industries.

These versatile, compact and self contained products can be used to measure and record parameters including temperature, pressure, relative humidity, acceleration, inclination, voltage and current.

The ability of data loggers to function with "mixed parameter" sensors further extends their capabilities.

Portable loggers typically comprise of signal conditioning electronics, one or more sensors (either internal or external) built-in memory unit, clock and internal battery.

Unit configurations include: single-channel; multiple-channel/single-parameter;p and multiple-channel/multiple-parameter (for example temperature and humidity, or temperature, humidity and pressure).

The ease with which loggers can be set up and data extracted has been a major catalyst for their increased use.

This is usually carried out in conjunction with a PC or lap top computer using dedicated software.

There are four main methods used, namely direct cable link, infra red, radio network and induction.

The latter three do not require any form of electrical connector so the sealing integrity of the logger is assured.

This is vitally important in harsh environments in the food, chemical and environmental industries.

A common software platform for different types of data loggers is vital, ensuring comprehensive and flexible exchange of data.

With increased demands on industries for traceability data integrity is also essential and data loggers are now available which support the latest standards for electronic signatures.

In order to conserve battery life, loggers use special low power electronics and can be set up to measure and record at discrete preset periods.

Depending on the application, sample rates are usually set anywhere between several times a second up to several days and therefore the total logging period is a function of this period and the internal memory size.

Depending on the design and setup, data may be stored until the memory is full (fill then stop) or stored on a continual basis with the older data being automatically replaced (first in- first out).

Data loggers with a "delayed start" feature can be set up to start logging at a predetermined time in the future, thereby preserving logging capability.

The start can either be set for some specific date or programmed to be "event" initiated, whereby the start will be triggered if measured parameter values go outside predetermined thresholds.

Design and packaging ingenuity is playing a vital role in an increasing number of hitherto difficult data logging applications.

For instance as sealing, temperature and enclosure material capabilities improve; portable units are now capable of withstanding the rigours of high temperature washing and chemical environments.

Modern communication technology is also rapidly increasing the use of data loggers, allowing the remote extraction of data, especially from unmanned and geographically remote and often hostile sites.

This can be achieved either using conventional modem-to-modem communication or via GSM if a PSTN telephone line is not available at the remote site.

On a more local basis, radiocommunication removes the need for the hard-wiring of data loggers in factories, warehouses and buildings This wireless technology means that the system offers significant savings in terms of wiring and installation costs, whilst providing the ultimate in flexibility.

Systems can be installed quickly and without any disruption to existing structures or buildings.

However, given the range of available data loggers it is surprising that in a number of key areas, especially in food and medicine, parameters such as temperature are still being manually taken with thermometers and the results written down.

Not only is this time consuming but it also relies too much on the operator and does not give a continuous supply of data.

There are still plenty of opportunities for data loggers and these flexible units will continue to flourish.

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