Humidity sensor
Version : 0.1
File: SMTHSver
DRAFT VERSION
SMARTEC CAPACITIVE HUMIDITY SENSOR.
The capacitive humidity sensor of Smartec is based on silicon technology on glass wafer.
Due to the use of this process it is possible to make sensors on a high volume scale on a low
cost way.
The Smartec humidity sensor consists of three layers. The base and top layer are conductive
and the layer in between is humidity sensitive polyimide. The selection of this sensitive
interface makes the sensor highly independent to temperature effects. The top layer has grid
like structure. The sensor converts the humidity into a capacitance. Due to the construction
the response to humidity is very fast (<15 sec) and the hysteresis very low (<2% RH)
Typical applications:
• Hygrometers, consumer goods
• Humidifiers and Dehumidifiers
• Medical applications
• Weather stations
• Automotive
• HVAC
• Food processing
• Room comfort control
Product Highlights.
• The Smartec capacitive humidity sensor measures from 0 to 100 % RH. In many
applications condensation on the sensor may occur. This has no effect on the
performance of the sensor but the response time while drying will be large.
• The linearity of the Smartec is within a band of 2 % in the range between 20 and 95
% RH.
• The response time is relatively fast so in case where this is needed the Smartec
humidity sensors can be applied (response time < 15 s.)
Specifications:
Measured @ 25 °C, Sensor excitation: 1V@ 20 kHz
Parameter Condition Min Typ Max Min Typ Max Unit
Capacitance 55% RH 310 330 350 170 180 190 pF
Sensitivity 20 - 95 % RH 0,6 0,34 pF/%RH
Hysteresis 20 -095 % RH 2 2 % RH
Linearity 20 - 95 % RH ±2 ±2 %RH
Response time 30 - 90 % RH 15 15 sec
Temp coeeficient 5 - 70 °C 0,15 0,16 0,17 0,07 pF/°C
Long term stability 0,2 0,5 %RH/year
Temperature range -40 120 -40 120 °C
Operating humidity range 0 100 0 100 % RH
Frequency range 1 100 1 100 kHz
HS07 HS08A
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SMARTEC BV, Delpratsingel 26 WWW.SMARTEC.NL
4811 AP BREDA, The Netherlands Tel: +31 (0)76 5205353
Humidity sensor
Version : 0.1
File: SMTHSver
DRAFT VERSION
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:
Cc = Cs + S *(Xrh – 55)
With: C
Cs = capacitance value at 55% RH (pF)
Xrh = measured Relative Humidity(%)
S = sensitivity
This means the Relative Humidity can be calculated by:
Due to the tolerance of Cs it is needed to perform a calibration. In the graph below the
response of the sensor is given
Basic Characteristic of HS07
400
380
360
340
320
300
280
Capac itanc e (pF)
260
240
0 10 20 30 40 50 60 70 80 90 100
Relative Humidity (% RH)
= measured capacitance(pF)
c
X
= (Cc - Cs)/S + 55
rh
The measurement range is between 10%
RH and 95% RH
S= 0,55
S= 0,60
S= 0,65
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SMARTEC BV, Delpratsingel 26 WWW.SMARTEC.NL
4811 AP BREDA, The Netherlands Tel: +31 (0)76 5205353
Humidity sensor
-
all sizes in mm.
Version : 0.1
File: SMTHSver
DRAFT VERSION
CALIBRATION.
Due to the high linearity of the humidity sensor it is only needed to calibrate on one point.
In one of the Smartec’s application notes (on www.smartec.nl, support shop) salt solutions
for calibration can be found. A poor mans solutions is to place the humidity sensor into a
refrigerator. Inside a refrigerator the humidity is always 100%.
The factory tests are done at 55% relative humidity. Depending on the application of the
humidity sensor calibration can be done at higher humidity level as well on lower humidity
level. The long term stability (0.2 %/yr) guarantees a stable working for over the years.
TOLERANCE.
The specified tolerance is the tolerance of the capacitor at 60% RH. This tolerance can be
considered as an effect of the production technology. When the capacitor is f.i. 2 % to high
(@ 0% RH) also the sensitivity will be around 2% to high.
LINEARITY.
The linearity is considered as the maximum deviation from a straight line between 0% RH
and 100% RH. In the condensing area some drift can be expected; but this drift is reversible.
The device is resistant against submerge in water.
MECHANICAL OUTLINE.
2.54
5
0.5 x 0.3
11
7
5
- do not touch active area or use glove
- base material: glass (0.3 mm)
- wires
ORDERING CODE:
SMTHS07
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SMARTEC BV, Delpratsingel 26 WWW.SMARTEC.NL
4811 AP BREDA, The Netherlands Tel: +31 (0)76 5205353
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