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Compare museum temperature and relative humidity monitoring dataloggers
by Rachel Perkins Arenstein
Knowledge is power. Nowhere is that more true than in museums, where knowing detailed knowledge about environmental conditions is paramount to preserving collections.
The primary tool for gathering environmental information such as temperature and relative humidity in a museum is the data logger. Because there are many dataloggers available for basic monitoring, outline your monitoring goals before choosing a logger. Planning ahead makes it far easier to choose a logger with the appropriate features at the right price. Conservators often undertake environmental monitoring to obtain general trend information to help develop environmental profile of a particular space or for specific projects. Dataloggers greatly expand the possibilities for environmental monitoring for specific projects such as the purchase of buffered storage or exhibition cases or installation or repair repair of heating, ventilation and air-conditioning (HVAC) systems. Dataloggers also allow you to measure the ability of a building to buffer the outside environment by allowing indoor conditions with outdoor climate data. For such projects, memory capacity and battery life are important, but may be outweighed by other needs such as size, display or alarm capability.
Determining goals is also essential to avoid wasting money on unnecessary features. Dataloggers prices range widely. Some cost less than $100, while others cost about $1,000, not including computer software and cables. Price generally reflects the quality of the sensor, the longevity of the battery, the durability of the casing and the flexibility of the software. Added features such as probes, alarms and portable download units add to the cost.
Consider the following factors when reviewing a logger's specifications. Please see the accompanying table for details.
Memory Capacity: Product literature describing memory capacity is often confusing. For instance, most manufacturers list the number of readings the logger will take and store. But many loggers require at least two channels: one to record temperature and another for relative humidity. Some loggers allow extra optional channels for features such as external probes. The more channels in use, the fewer readings collected. To actually compare different loggers, it is essential to know if the number provided by a manufacturer is the real total.
Battery Life: At a minimum, a logger battery should provide one full year of monitoring. Consult the manufacturer to check that the calculation for battery longevity is factored when the logger is working to capacity. For example, a logger with a one-year battery life may not last an entire year if the logger takes frequent readings during that period. It is critical make sure the logger saves data even if the battery dies.
Sensor Accuracy: For monitoring environmental units such as HVAC systems, freezers and buffered cases, sensor accuracy and operating range are important. Not all loggers are guaranteed accurate across the range of temperature and humidity they record. A logger calibrated at three points across its range should take accurate high and low readings, while a logger calibrated at one midpoint closer to ambient temperature may not be accurate at the extremes. It is important to determine if the application requires accuracy within 0.5% or 5%RH. Some loggers allow the user to recalibrate, but most can be sent back to the manufacturer if they are not performing within their set parameters. The manufacturer should be consulted to determine if the accuracy of temperature readings listed is given for the entire range or for ambient temperature.
Size, Appearance and Construction: For projects designed to evaluate the environment in vitrines, buffered frame enclosures, storage cases and shipping crates the logger's size may be a determining factor. Casings are normally made of hard plastic and the colors and shapes vary. The casing of the logger should be durable and the sensor well protected. The Hobo Pro is the only weatherproof model suitable for outdoor use. The smallest loggers may be the most unobtrusive, but larger loggers generally can be screwed in place to fasten them securely, which is important when the units are installed in public spaces.
Display: Some projects may require a visible display of real-time data for spot checks. While the display is extremely useful, it often greatly shortens battery life.
Alarms: Some loggers have either visible or audible alarms to alert staff when pre-set parameters are exceeded. This feature is extremely useful in areas where a leak or other sudden change could cause severe damage. Alarms also can reduce battery life.
Probes: Some loggers have optional external probes. These attachments are unobtrusive and can be snaked into hard to reach spots, leaving the logger itself in a more accessible location for downloading.
Download Options: Data can be retrieved by bringing a unit to a desktop computer or by connecting to a laptop in place. Some loggers also can be downloaded via a small handheld device such as a portable 'shuttle' or Palm Pilot. This is an alternative to the visible display when frequent spot checks are necessary. For monitoring sealed environments, manufacturers are developing loggers with infrared ports for wireless data transmission.
Download Speed: Speed becomes a factor when numerous loggers are needed and data will be retrieved frequently. The speed of data transmission varies with memory size, type of interface cable and software, as well as the speed of the personal computer.
Software Capabilities: Hardware is important, but software makes the differences between loggers even more apparent. Some programs are more intuitive to use than others, but all tend to be reasonably user friendly. All of the models were tested on a PC. Consult manufacturers to determine whether MacIntosh software is available. Look for easy installation, launching, data retrieval and graph manipulation.
All of the units allow users to delay the start logging with the exception of the Trak-R and XerIC. Almost all allowed the user to choose between stopping logging after a certain number of readings, stopping when full or never stopping (i.e. wrap around). An essential function is the ability to back up or retrieve data from the logger without having to re-launch. This provides one long uninterrupted graph rather than many short ones. All the models allowed for this.
There are also several key graphing features: the ability to manipulate the X and Y axes to compare graphs, the ability to print the graph without having to export the data to a secondary program, and the ability to label the graph. The program should clearly display the time, date and year of the readings. It is often helpful to be able to view data in tabulated form and there may be occasions when it is useful to be able to export data to a spreadsheet program such as Excel. The ability to rename and organize the downloaded files is also convenient. Some programs only allow for names of eight characters while others allow up to 24.
Service and Technical Support: The reputation of the manufacturer and the quality of their service and technical support factor into the decision. Look for firms with a product specialist (preferably more than one) who understands museum needs and can accurately answer any questions about their products. Several companies allow tests of their software via the Internet and many will send their logger for a 30-day free trial. All the products listed above come from reputable companies that were extremely helpful in lending their products and time.
Datalogger files can become useless if not kept organized. At the American Museum of Natural History several logs are kept to organize relevant information. An inventory log of all monitoring equipment lists the manufacturer, model and serial numbers and dates of calibration. A placement log records by model and serial number the launch settings to indicate how long it will record, the date it was placed, date retrieved, the location, and the file name so the data can be found on the computer. The location of the loggers can be marked on an accompanying floor plan. Finally, an event log is maintained to record any unusual occurrences or general trends noted such as leaks, construction, HVAC malfunctions, steam or electricity outages or exterior climatic changes that may help explain anomalous logger readings. For even the most reliable loggers it is best to set a regular downloading schedule (e.g. once a month, every three months) to prevent loss of data.
I would like to thank Judith Levinson and the Conservation Staff at the American Museum of Natural History for their direction and support, as well as the logger manufacturers for generously allowing the American Museum of Natural History to borrow their products and the specialists listed above for their time and expertise.
Rachael Perkins Arenstein was Assistant Conservator at the American Museum of Natural History in New York City. She is currently the Assistant Conservator at the Peabody Museum of Archaeology and Ethnology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, Tel: (617) 495-2487, e-mail:email@example.com.
This article is based on comparisons, evaluations and testing of loggers at the American Museum of Natural History in New York City. The author's recommendations are based on this work.
This article was reprinted with permission. It was initially published in AIC News, January 2001 pp. 16-19.
References and Sources:
Daly, Gregg M., and Hugh J. Flye, 2000. "Dataloggers Deliver" In: Engineered Systems 17:8, pp.84-89
National Park Service. 1993. Conserve-O-Gram 3:3
ACR SmartReader 2 - Greg Basso, Cascade Group Inc., personal communication and June Wheeler, Herzog /Wheeler & Associates, personal communication.
Dickson TP-120 - Chris Sorensen, Dickson, personal communication
Tinyview - Steven Weintraub, Craig Oleszewski, and Richard McCoy, Art Preservation Services, personal communication.
Hanwell Humbug - Greg Basso, Cascade Group Inc., personal communication.
Langan XerIC Measurer - Lee Langan, Langan Products Inc. personal communication
Onset Hobo H8 and Hobo Pro Series - Scott Ellis and Hugh Flye, Onset Computer Corporation, personal communication.
Trak-R TL-2000 - Gene Giffords, Trak-R Logger, personal communication.
Veriteq Spectrum 2000 - Frits de Geest, Veriteq Instruments Inc., personal communication.
Westronics Rustrak Scout - Lou Barker, Westronics Inc., personal communication.
Is Ethafoam safe to use in your museum?
by Helen Alten
Just when we are sure that we have found the perfect material, something happens.
Polyethylene foam (the most popular brand is Ethafoam) is the darling storage/packing/display foam of the museum world. They may not be as perfect as we thought.
There is mounting evidence that the buyer must do some homework.
In 1996 Dow, manufacturer of Ethafoam, stopped using CO2 to make the foam's bubbles. The new gases are not as inert. Apparently after switching, a truckload of polyethylene foam blew up. Since then, fine pinholes, the size of a number 5 insect pin, perforate the foam to release gases.
At the Science Museum of Minnesota, old (age unknown) polyethylene foam in a warehouse yellowed. This could be from poor storage conditions or contact with poor materials.
Old (age unknown) polyethylene foam has lost its cushioning capabilities; it no longer springs back, but retains a finger indentation.
At the Illinois State Museum, staff noticed that polyethylene foam shelf liner fluoresced under black light under protein materials. Only some materials, inconsistently showed this phenomenon. More than one color of fluorescence was noted. It seemed to occur with polyethylene foam liner bought at different times, possibly from different vendors. Occurred in more than one storage area with vastly different collections.
Many companies make polyethylene foam. Different gases and different processes are used.
At this point, the two safest polyethylene foams to use may be Zotefoam and Volara. Zotefoam's bubbles are made with nitrogen. Volara is an electron-radiation cross-linked foam. It is not made by blowing gases into it to form bubbles.