6
User Manual EE371 Compact Dew Point Senor
3.2 Auto-Calibration
Dew point temperatures ranging from -60 to -20 °C (-76...-4 °F) at room temperatures correspond to
relative humidities of 0.08 to 5.37 % RH.
To guarantee the accuracy at the lowest humidity, even the smallest drift effects in the humidity sensing
element must be compensated.
A special auto-calibration method is used to compensate the usual drift effects, which leads to high-
precision measurements even at the lowest dew point temperatures.
Auto-calibration is carried out every 30 minutes and takes approx. 3 minutes.
When putting the device into operation after a long interruption, the regular auto-calibration procedure
might require a long time to bring the device within specs. Therefore, an advanced auto-calibration
mechanism takes place 5 min after power on.This advanced auto-calibration mechanism takes a
little bit longer than the regular auto-calibration and is performed up to 5 times during the first hour of
operation.
During auto-calibration, the analogue output switches to the state
Frozen output signal, keeping the last measured value (default behaviour).
3.3 Measuring Range and Accuracy
The EE371 has an accuracy of ±2 °C specified within the measuring range -60...60 °C dew point.
Measuring signal limitation:
at medium temperature
≤20 °C (≤68 °F)
: Td limitation = -80 °C (-112 °F)
at medium temperature >20 °C (>68 °F): Td limitation = medium temperature - 100 °C (-148 °F)
e.g. at medium temperature 40 °C (104 °F) the measuring signal is limited at -60 °C (-76 °F) dew point.
60
40
20
0
-20
-40
-60
-80
0
10
20
30
40
50
60
-10
-20
-30
-40
Accuracy
≤
±2 °C Td
Accuracy not specified
Measurement range
limitation dew point
Medium temperature [°C]
Dew point temperature Td [°C]
Fig. 1
Dew point measurement range and specified accuracy
The maximum scaling of the analogue output is -100...80 °C (-148...176 °F) dew point.