Industrial Temperature Primer

Chapter 4.

Datalogging

In many industrial applications it is often necessary to record temperatures for permanent records due to government or manufacturing requirements or to simply provide historical data that may later help determine problems within a system.

Data collection of temperature readings in industry vary from sophisticated DCS systems (Distributed Control Systems) which do both data logging and control usually of many process points simultaneously to simple manual systems using inexpensive portable indicators.

The most inexpensive portable indicators do not provide any "recording" or memory features. Readings from these instruments must be recorded by hand. Some portable indicators now are available with memory so that a number of measurements may be taken into memory and later downloaded into personal computers for permanent records.

Another popular way to record data from temperature sensors is by chart recorder. Chart recorders have been around for a long time and still have application in today's process marketplace. Round chart recorders take thermocouple and RTD signals directly or analog process signals from sensors using a transmitter. The advantage of round chart recorders is that the charts are graduated into precise time periods for those who require records by the day, week, or hour on separate charts. Strip chart recorders, on the other hand, offer the ability to input many more inputs and read them by scanning and then printing. Many of today's chart recorders are what is called "Hybrid" recorders. These recorders offer many more functions and abilities that the standard chart recorders can't.

Hybrid recorders offer various recording modes such as analog trending where a pen or dotting mechanism "draws" a recorded input for each channel. Each channel, in most cases, can be charted in a different color. This is important when recording a number of different points as it allows simple identification of the point the technician is trying to read. Hybrid recorders also offer digital recording modes which alphanumerically list sensor measurement with time stamps, tag numbers, point numbers, etc. Hybrid recorders also offer the combination of digital and analog trend recording. In this mode, the recorder can be programmed to trend record for an adjustable time period and then automatically print out a chart of measurement readings at specified time intervals. These modern day recorders usually offer digital readouts as well that give a digital indication of the process temperature of selected points or of scanned points. Many additional features such as alarm outputs, change of print color in alarm condition, self diagnostics, etc. are available on Hybrid recorders.

Distributed control systems also offer datalogging as a part of their overall capabilities. Since these systems are computer based, the datalogging functions are programmable to almost any configuration you may need.