TESTO 6681 Instruction Manual page 39

1.3.3.6 Self adjustment of testo 6615 trace humidity
probe
Conventional trace humidity probes show a steep rise in measuring
uncertainty at low humidities. In the testo 6615 trace humidity probe, these
measuring uncertainties are corrected by means of an automatic self-
adjustment process. This means that extremely accurate measuring results
are also attained to -60 °Ctd.
To this end, a temperature sensor is fitted on the back of the testo 6615
which is used as a heater. A humidity and temperature value pair is taken in
both the unheated and heated state. The deviation of the probe obtained
from these pairs of values is automatically corrected.
The graph shows the effect of the self-adjustment, e.g. during the Init. phase.
1 Self-adjustment
2
Correction of measurement value
3 Process dew point temperature
testo 6681
- 1.3 Commissioning 39