Datasheet
Datasheet SHT7x
www.sensirion.com Version 4.3 – May 2010 8/11
The values given in Table 6 are optimized coefficients for
V4 sensors. The parameter set for V3 sensors, which has
been proposed in earlier datasheets, still applies and is
provided by Sensirion upon request. Values higher than
99%RH indicate fully saturated air and must be processed
and displayed as 100%RH
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. Please note that the humidity
sensor has no significant voltage dependency.
0%
20%
40%
60%
80%
100%
0 500 1000 1500 2000 2500 3000 3500
SO
RH
sensor readout (12bit)
Relative Humidity
Figure 13: Conversion from SO
RH
to relative humidity
4.2 Temperature compensation of Humidity Signal
For temperatures significantly different from 25°C (~77°F)
the humidity signal requires temperature compensation.
The temperature correction corresponds roughly to
0.12%RH/°C @ 50%RH. Coefficients for the temperature
compensation are given in Table 8.
linearRH21Ctrue
RHSOtt25TRH
SO
RH
t
1
t
2
12 bit 0.01 0.00008
8 bit 0.01 0.00128
Table 7: Temperature compensation coefficients
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4.3 Temperature
The band-gap PTAT (Proportional To Absolute
Temperature) temperature sensor is very linear by design.
Use the following formula to convert digital readout (SO
T
)
to temperature value, with coefficients given in Table 9:
T21
SOddT
VDD d
1
(°C) d
1
(°F) SO
T
d
2
(°C) d
2
(°F)
5V -40.1 -40.2 14bit 0.01 0.018
4V -39.8 -39.6
12bit 0.04 0.072
3.5V -39.7 -39.5
3V -39.6 -39.3
2.5V -39.4 -38.9
Table 8: Temperature conversion coefficients
15
.
13
If wetted excessively (strong condensation of water on sensor surface),
sensor output signal can drop below 100%RH (even below 0%RH in some
cases), but the sensor will recover completely when water droplets
evaporate. The sensor is not damaged by water immersion or condensation.
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Coefficients apply both to V3 as well as to V4 sensors.
4.4 Dew Point
SHT7x is not measuring dew point directly, however dew
point can be derived from humidity and temperature
readings. Since humidity and temperature are both
measured on the same monolithic chip, the SHT7x allows
superb dew point measurements.
For dew point (T
d
) calculations there are various formulas
to be applied, most of them quite complicated. For the
temperature range of -40 – 50°C the following
approximation provides good accuracy with parameters
given in Table 10:
TT
Tm
100%
RH
lnm
TT
Tm
100%
RH
ln
TTRH,T
n
n
nd
Temperature Range Tn (°C) m
Above water, 0 – 50°C 243.12 17.62
Above ice, -40 – 0°C 272.62 22.46
Table 9: Parameters for dew point (T
d
) calculation.
Please note that “ln(…)” denotes the natural logarithm. For
RH and T the linearized and compensated values for
relative humidity and temperature shall be applied.
For more information on dew point calculation see
Application Note “Introduction to Humidity”.
5 Environmental Stability
If sensors are qualified for assemblies or devices, please
make sure that they experience same conditions as the
reference sensor. It should be taken into account that
response times in assemblies may be longer, hence
enough dwell time for the measurement shall be granted.
For detailed information please consult Application Note
“Testing Guide”.
SHT7x have been tested according to the test conditions
given in Table 11. Sensor performance under other test
conditions cannot be guaranteed and is not part of the
sensor specifications. Especially, no guarantee can be
given for sensor performance in the field or for customer’s
specific application.
Please contact Sensirion for detailed information.
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Temperature coefficients have slightly been adjusted compared to datasheet
SHTxx version 3.01. Coefficients apply to V3 as well as V4 sensors.