The PEM2 vs. Other Dataloggers

PEM2When times are tough, every penny counts. We at IPI are sometimes asked about the differences between the PEM2 and less expensive dataloggers. Preservation of collections requires a source of reliable environmental data. There are many ways to collect such data and by pointing out the advantages of the PEM2, IPI in no way pretends that it is the only reliable source. However, the PEM2 was designed from the ground up to be the data-gathering element in a set of tools for sustainable climate management. It was created by preservation experts exclusively for use by collections care professionals. Its accuracy, time-saving features, long-term reliability and tight integration with IPI’s unique graphing software and preservation metrics make it a better value than other devices whose initial cost advantage may prove a false economy. Professionals in every field choose tools that help them do their jobs faster and better, and managing the preservation environment is no exception.

First of all, the PEM2 is a superior measuring instrument with demonstrated accuracy.  It has much better humidity accuracy because of the quality of the RH and temperature sensors and the fact that each PEM2 is individually calibrated on a NIST-traceable calibration device, guaranteed by a certificate issued with each logger and signed by a test technician. IPI claims a maximum % RH error of +/- 2%, but the PEM2s shipping today typically perform to within 1% of the true RH reading. Less expensive loggers often have +/- 3.5 % RH maximum error and are not individually calibrated. PEM2s are built in the USA and unlike some less expensive loggers, use industrial grade components throughout. Industrial grade parts are less likely to fail at high or low temperatures. PEM2s are green; they are made with special parts and solders that comply with international RoHS (Reduction of Hazardous Substances) specifications. You will not find mercury or lead inside a PEM2 or a “do not dispose of in trash” symbol. They also feature software compensation for low temperature that means the PEM2 can be trusted to give accurate humidity readings in cold vaults and freezers.

Certifiable accuracy matters to collections care professionals for two reasons: First, there are humidity ranges (mainly in very dry circumstances and moderately humid circumstances) where a few % RH each way can make the difference in whether collections will be damaged or not, or whether immediate corrective action is required. Second, humidity measurements from two different sources (for example, a datalogger placed by collection care staff vs. readings from sensors attached to a building management computer system) rarely agree exactly. Disagreements of the ‘he said / she said’ variety between RH measurements are extremely common.  It is human nature (and sometimes rather more convenient) to question the ‘other’ instrument. That is why it is important to have a quality instrument and some documentation to back it up. If a datalogger is dismissed by facilities professionals or engineers as inaccurate, its purchase price or the time spent collecting data is wasted.

Accuracy aside, the most valuable aspects of the PEM2 are the time it saves and the preservation knowledge and support behind it. The PEM2 is the easiest device to launch and to retrieve data from of any datalogger—simply insert any USB flash drive (memory stick). Typical once-a-month data retrieval takes a few seconds, with no fussy setup using proprietary software. PEM2 users rate this feature as their favorite. Add up the time spent launching and retrieving data from inexpensive loggers using their proprietary software and initial price savings are quickly eaten up in hourly salaries. PEM2s have a display, a feature lacking in most less expensive dataloggers. Users tell IPI that displays are very useful in everyday preservation practice. PEM2 batteries last for years and can store up to 20 years’ worth of data—less expensive logger batteries typically have 1-year battery life and limited data storage. Gaps in data from less expensive loggers that originate from a combination of dead batteries and cumbersome file naming confusion undermine the very purpose of having dataloggers in the first place. All these are reflections of the fact that the PEM2 was designed for one job: collecting environmental data in museums, libraries and archives.

The final advantage of the PEM2 is its unparalleled customer support. IPI has a generous warranty and always responds promptly to requests for technical support through e-mails ( and phone calls. The best part of PEM2 support is that there is a team of preservation experts behind it. Often conversations turn from how to resolve a data-gathering problem to more pertinent questions about the meaning of the data and the behavior of HVAC systems. IPI regards tech support as a way to fulfill its mission of supporting preservation with technology and research. Adding together all of the factors, PEM2s offer superior value compared to devices that may cost less initially, but also deliver fewer of the things collections care professionals need to do their job well.