Volume 15, Number 7
Nov 1991

More Easy Environmental Monitoring:
Dataloggers

Last time we talked about a direct readout device that measures temperature and humidity with minimum and maximum memories, which could be used as a manual monitoring system. This time we are going to examine a relatively new product called a datalogger.

A datalogger is a small microcomputer no bigger than a standard audio cassette, capable of recording temperature and humidity over a specific time period. The data is collected and stored in the memory of this little unit and can be downloaded at the end of the period to a personal computer or sent to a processing center for analysis. The data can be loaded into a spreadsheet for all types of formula-based calculations and various types of graphs. The period over which the unit will record data depends on how often you want the unit to read and record the temperature and humidity. For example, a standard unit is capable of 32,000 data points or 266 hours of readings if readings are taken every minute. If you only wanted to record the temperature and humidity every hour, you could collect almost two years' worth of data. My advice would be to set the unit for reading every five minutes and process the data at least monthly.

These units can take the place of hygrothermographs and offer many advantages. They are more accurate than hygrothermographs, and more convenient too. Since they operate electronically rather than mechanically, they do not require paper and pen changes or calibration, and they do not have to be wound. The batteries will last for ten years. The best feature is that once the data is gathered, it can be analyzed many different ways, and can even be sent to a specialist for professional analysis.

Another valuable use for dataloggers, besides monitoring sites within a building, is monitoring conditions inside the crate or travelling container for artifacts being lent to other institutions. It would certainly make the insurance agencies less frantic to know that a datalogger was attached, because if damage occurred as a result of temperature or humidity problems, these problems could be tracked to the source.

I have evaluated three widely used brands of dataloggers, The first two are about the same price and the third one is almost double that price.

The first unit, the ACR, is manufactured in Canada and is distributed in this country by two major sources. One is Dickson, an international distributor of all types of recording meters, and the other is Herzog & Wheeler, an engineering firm in Minnesota. The price of the Herzog and Wheeler unit is lower, around $725 for the datalogger and $150 for the software. I recommend Joan Wheeler as a contact. Her emphasis is on support, and she will be there if you have any questions or need a helping hand. The ACR unit has been in use for some time and was originally designed as a tool for engineers to diagnose problems with mechanical equipment in industrial applications. It is only recently that it was offered for use by museums, libraries and historic buildings. One of the strongest attributes of this unit is its easy computer interface. It is marketed with a demo disk which is an animated color presentation that is both informative and interesting. This demo disk also contains a computerized specification section that allows you to pick the units that are right and even print out specification sheets. (They really did a great job!) The computer program that you buy as a part of the datalogger is also very good. It is easy to use, menu-driven, and capable of automatically producing many graphs and statistics as standard fare. I have spoken to people who are not what I call computer proficient, and they find this program easy and functional.

The second unit, DATABEAR, is the brain child of Lee Langan, a genius of a guy with an incredible scientific mind. This unit has some advantages over the ACR in terms of hardware. The DataBear has a real-time clock, which makes processing the data easier. It also has a better humidity sensor, called a Zerotron, which was invented by Dr. Fenner. Dr. Fenner noticed a characteristic of the African Geranium, whereby the plant would expel its seed into the air. The material responsible for this action was a cellulose crystalline substance that reacts predictably as the relative humidity changes. The Zerotron has been functioning reliably for over 15 years in various applications. The longest life of the type of humidity sensors being used in the other devices that I have personally witnessed is five years. Lee has developed an intensive computer program for the Macintosh which can produce statistics and graphs, but he has not done much for people with IBM type machines except to transfer the data via an ASCII file which can be loaded into a spreadsheet. This unit is available direct from Langan and costs about $750.

The third unit is manufactured by Rustrack and is called the RANGER. They have two units available, but the Ranger 2 is more on a level with the other ones reviewed here in terms of memory and feasibility. The unique feature about this unit is what is called adaptive memory storage. This means the unit only records data if a change takes place, which increases the amount of time that you can log data. The major drawback to this unit is that you have to buy the recording part of the unit and the sensors as separate units. This causes the price to be about double that of the other two units.

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