Rebecca, I own two recording hygrothermographs. One has a single hair bundle for monitoring %RH and the other has 8 hair bundles; both use bi-metallic strips for recording temperature. In addition, I own three data loggers. Two were designed to work with Macintosh computers, and one was designed to work with PC's. And then, there is the Micronta temp/%RH LCD device from Radio Shack. The Radio Shack device (manufactured in China) cost about $30.00; the other units cost from approx. $400 - 900. Bi-metallic strips are about as good as it gets. Simple technology; as close to bulletproof as it gets in this game. Hair bundles are different. They are as accurate as the last re-callibration, so long as there has not been a major humidity change (rain storm, for instance). Data loggers are generally superior to paper chart, recording- hygrothermographs, in my opinion. Data loggers have their own problems, to be sure, but I have the capacity to calibrate the sensors. These are containers of saturated salts into which I may introduce the sensors. The saturated salts, and the temperatures, are thus known, and if the sensors indicate drift, the software can be notified (in a sense) and appropriate changes may be made to the formulae which interpret incoming data. Recording hygrothermographs may provide a "written" record of change in temperature and relative humidity over time. Data loggers provide the same information in a digital format which permits a degree of analysis of conditions which is not possible with paper chart recorders. Arguements are raised to the effect that data loggers do not provide a continuous record, and that recording hygrothermographs do provide such a record. Examine a paper chart from a museum. The paper chart machine may be continuous, but the physical plant (furnace/air conditioner) kicks in or out in 15 - 30 minute units of time. A data logger set to reach out and record every 15 minutes, or 30 minutes, will provide a useful record. In addition, data loggers may be tied into an alarm system more easily than paper chart recorders. This may wake a museum director or curator up in the middle of the night, but that may be a small price to pay. Jack C. Thompson Thompson Conservation Lab Portland, OR [log in to unmask] On Wed, 13 Mar 1996, Rebecca Patchett wrote: > Hello. I have recently become aware of the relatively inexpensive option of > purchasing RH and temp. sensors (known as data loggers) that record > environmental data continuously and store it internally in a microchip (ex, > ONSET brand). This data is downloaded into a computer at a later time in > order for it to be read. The sensors are tiny, and very affordable compared > to the recording hygrothermographs that are larger and use graph paper. > > I believe the data loggers were originally designed for biological studies, > field use, and the like. I was wondering if anyone has experience with these > loggers in museums. If so, are they worthwhile for museum > applications? How do they compare with the "standard" recording > hygrothermographs I/we are more familiar with? How is the accuracy of these > small units? We are considering them as a cost effective option for a small > museum. Any comments are greatly appreciated! > > Thank you, > > Rebecca Patchett > Lilah C. Holden Elephant Museum > Portland, OR > e-mail: [log in to unmask] >