In on-site calibrations, it is important to
allow enough time for the calibrator and probe temperatures to stabilize. A two-point
calibration takes about 30 minutes … 2 hours, depending on the difference between
transportation or process temperature (with probes removed from the process) and the
calibration site. If there are several instruments at the same site needing frequent
calibration, it is useful to know the respective stabilization times.
Figure 1. Stabilization time when probe is removed
from process. In the following temperature and humidity stabilization example, a humidity probe is
transferred from an oven temperature of 75 °C (167 °F) to a suitable hole in the NaCl salt
chamber, which is at room temperature. After 40 minutes, the humidity reading differs by
0.2 %RH from the final reading.Figure 2. Stabilization time when transportation
and calibration site temperatures are different. In the following example, the calibrator (without the LiCl) is brought in from a
transportation temperature of +5 °C (41 °F) to room temperature. A humidity probe stored at
room temperature is then inserted into a suitable hole in the NaCl salt chamber. After 40
minutes, the reading differs by 1.4 %RH from the final reading.
