Datasheet

Humidity sensor
Version : 0.1
File: SMTHSver
DRAFT VERSION
- 2 -
SMARTEC BV, Delpratsingel 26 WWW.SMARTEC.NL
4811 AP BREDA, The Netherlands Tel: [phone]
Understanding the specifications.
The measuring of humidity is difficult. Generally the humidity in air is measured as the
fraction of the maximum amount of water that air can absorbed at a certain temperature. At
atmospheric conditions and a given temperature this fraction can vary between 0 (absolute
dry) and 100% (the point where condensation will begin to form). This relative humidity is
only valid at a certain temperature and atmospheric pressure. Therefore it is important that a
humidity sensor should not be affected by either temperature or pressure. Many sensing
techniques, such as mechanical devices and resistive type sensors are temperature
dependent and even the wet and dry bulb is pressure dependent.
The HS07 humidity sensors can by used in a wide range of applications. The sensor can be
used for low cost commercial application as well in medical and industrial products. To
achieve more feeling for the specifications as give above some details are given below.
ABOUT THE RELATION BETWEEN CAPACITANCE AND THE RELATIVE HUMIDITY.
The relation between the measured capacitance and the Relative Humidity (RH) is depicted
below:
C
c
= C
s
+ S *(X
rh
– 55)
With: C
c
= measured capacitance(pF)
C
s
= capacitance value at 55% RH (pF)
X
rh
= measured Relative Humidity(%)
S = sensitivity
This means the Relative Humidity can be calculated by:
X
rh
= (C
c
- C
s
)/S + 55
Due to the tolerance of C
s
it is needed to perform a calibration. In the graph below the
response of the sensor is given
The measurement range is between 10%
RH and 95% RH
Basic Characteristic of HS07
240
260
280
300
320
340
360
380
400
0 10 20 30 40 50 60 70 80 90 100
Relative Humidity (% RH)
Capacitance (pF)
S= 0,55
S= 0,60
S= 0,65