By Chris Sorensen, VP, Dickson Company
In recent years manufacturers of instruments used for temperature and humidity monitoring in pharmaceutical applications have added to the number of ways that data can be displayed. Size of display, graphing capabilities, and data downloading are handled differently in different models and brands of instruments. Taking the time to look at all data display options is advised, because what works well in one pharmaceutical plant might not work or might be overkill for another pharmaceutical processor.
Many pharmaceutical processors still favor chart recorders, especially ones with larger 8 inches charts, because of the instantaneous visual clues that these can provide as to whether readings are in acceptable ranges, as well as the detailed information on continuous readings recorded in each chart. These have recently become popular again with the addition of battery operated versions that enable maximum flexibility in placing the recorders throughout a plant or lab.
Now however, there are also large display data loggers with full graphing capabilities, sometimes referred to as Paperless Chart Recorders or Paperless Recorders. Like the traditional paper-based chart recorder, these digital displays are large enough to produce a graph with complete information on continuous temperature and/or humidity over a given time period. Unlike the paper-based systems, large display data loggers do not require charts or pens. Moreover, the graphs on large display data loggers can be scrolled to view older data, or to select different temperature ranges to display data in even greater resolution. Considering the amount of data they provide, large display data loggers are relatively compact. Like most data loggers, the large display types allow one to download data to a PC, but if your application doesn't require you to do so you don't need to buy software for that unit.
Smaller display data loggers are not able to provide the complete information that is standard on the larger display models. However, even the smaller data logger displays do provide current readings as well as what the minimum and maximum values have been over a period of time. For many, that is enough information to make a decision, especially since data can be downloaded to view complete information.
Whether the data display is large or small, data loggers have other inherent advantages compared to chart recorders. First, because data is stored electronically it is easier to generate data backups. With chart recorders, if the chart is lost it usually means that the data records are also lost, unless cumbersome and time-consuming photocopying of all charts is a standard operating procedure. Second, the pen marking system used on chart recorders makes them more vulnerable to mechanical shocks than data loggers. The drift found during data logger calibrations is usually less than that found with chart recorders. Third, compared to chart recorders, most data loggers are light and easy to move around. Fourth, there are data logger models that incorporate flash card technology that allows one to keep the logger in place and simply remove quarter-sized flash cards for data downloading. Last, data loggers provide "Low Battery" indicators that allow ample time for battery changes, whereas chart recorders might die out without warning such that data is lost.
In real world applications, the choice of one type of data display vs. another often has quite a bit to do with the operational details of how a particular monitoring instrument is used. For example, Brice Murri, Research Chemist with Bend Research of Bend, Oregon, switched his plant from chart recorders to data loggers, and explains that the ability to download data was paramount.
"Charts were especially messy because we have lab technicians that liked to stick the charts into their notebooks that showed the temperature and humidity during design periods. We have six or seven technicians that each want to have a copy of what the conditions are for their samples. A downloadable program that is printed out six or seven times solves this problem."
"Our system is configured with a download cable that goes right into the RS 232 port of the computer. This download cable is taking data from three data loggers. The large screen just gives us a visual over a certain time period, either set for the last 8 hours or the last 24 hours. It's when we download all the data points that we see what ALL the data is. Nonetheless, the large display is a good reality check. It's always good to see the temperature and humidity at the current time without having to download it, just as a visual check. People go into check the display four times a workday and it gets downloaded twice a day, for each of our instruments. That means we do six downloads a day at most, depending on whether we have samples being monitored or not."
"Humidity controls are very important to our application, which is drug polymer mixtures. The data loggers we selected have two visual output options-one showing just the temperature and humidity reading and another that shows a graph of the data points for the entire time the instrument is set for. We usually keep our loggers in the graph mode so you can see at a glance what has been happening. The numbers are actually quite big and you can see them from far away."
"The system we selected also has the advantage of keeping data even when the battery for the display is used up. The memory of the logger is quite large and it keeps data until it is downloaded. At first, before you realize the data is still in there, you might get alarmed as we did the first time our display batteries died. But the display only requires a 9-volt battery and it's pretty straightforward to maintain."
"The strong recommendation I have is to make sure that you get data loggers recalibrated to NIST certified standards on at least a yearly basis. Some people think that data loggers don't drift, but they do."
Of course, there are many other differences in data logger features that should be considered at the time of purchase, in addition to data display options. For example, some data loggers have remote probes that are critical in certain pharmaceutical applications. Selecting models that are optimized for the temperature ranges that need to be monitored in your particular processing plant is always important. These considerations among others, combined with choosing the best data display options for your processes, are such that you should make sure you are considering the full range of data logger or chart recorder options available. There is no one-size-fits-all solution--- do your homework!
About the author: Chris Sorensen is VP of Dickson Company (www.dicksonweb.com). Inquiries can be directed to firstname.lastname@example.org, 630.543.3747, FAX 630.543.0498.