LogTag Recorders LogTag Analyzer Temperature Recorder - Manual (Page 169)

Chapter 10 Appendix 169
Sensor Responsiveness
Temperature sensors typically respond to changes in the environment temperature in a
logarithmic way and as such you will find that the responsiveness of temperature sensors
(how quickly a sensor responds to an environmental temperature change) is expressed in
terms of T90. T90 represents the time it takes for a logger to respond to 90% of the
actual change of the environmental temperature.
For example, if the actual environment temperature suddenly changed from 15° to 45°
and the T90 of the sensor was 30 minutes, then 30 minutes after this sudden change the
sensor would be reading (15 + (45 - 15) * 0.90) 42°. In reality, it is rare for the
temperature of an environment to suddenly change to a very different temperature and
then suddenly change again, usually it is a gradual incremental process.
For example, if the actual environment temperature changed from 15° to 45° over a
period of 5 hours in a linear fashion, that is after 2 hours the temperature was 27° and
after 4 hours the temperature was 39°, and the T90 of the sensor was 30 minutes, then
when after 5 hours of this temperature change, that is the actual environment
temperature was 45°, the sensor would be reading 44.7°.
LogTag products are designed to produce rapid response to environmental changes. For
example, the TRIX-8 model achieves a rapid response to temperature changes because
the actual sensor element is external to the logger body itself. The T90 of the LogTag
TRIX-8 is typically less than 5 minutes in moving air, which is very responsive as some
internal sensor temperature recorders can take up to an hour for the T90 of the
temperature change to be recorded.