Potential problems associated with the Rustrak Ranger data logger's data storage technique

To maximize the 8 kilobyte memory of the Rustrak Ranger data logger, a patented technique called adaptive storage was used. With adaptive storage, the data logger predicts the value of an incoming reading. Based on previously stored readings, the data logger predicts the next reading to be constant, linear, or exponential. If the reading falls outside a window surrounding the predictions, it is stored; otherwise, it is discarded. The size of the window affects the rate at which the readings are stored, and thus is adjusted so data can be collected for the specified sampling time. If the windows are made too large, there is a resultant loss in the resolution of the data. The characteristics of the instrument and the contaminant or physical agent being measured (i.e., air contaminant versus noise) also affect data resolution. In this evaluation, previously collected exposure data (air monitoring) were sent by a computer to the Rustrak Ranger for recording. To determine the effect of the sampling time on resolution, the recorded data were analyzed using two different methods. Sampling times varied from 2 to 120 minutes. These tests showed poor resolution for sampling times as short as 30 minutes, indicating that the Rustrak Ranger may not be suitable for certain types of sampling schemes. However, if used within its limitations, this data logger is a valuable tool for recording real-time industrial hygiene data.