SHT71 SENSIRION, SHT71 Datasheet - Page 3

Humidity Sensor

SHT71

Manufacturer Part Number
SHT71
Description
Humidity Sensor
Manufacturer
SENSIRION
Datasheet

Specifications of SHT71

Sensing Accuracy
3%
Sensor Output
Digital
Sensor Terminals
Through Hole
Peak Reflow Compatible (260 C)
Yes
Terminal Type
PCB Surface Mount
Humidity Range
0 To 100% RH
Response Time
8s
Humidity Accuracy ±
3%
Rohs Compliant
Yes
Leaded Process Compatible
Yes
Package / Case
4-SIP
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Users Guide SHT7x
www.sensirion.com
1 Application Information
1.1
Sensor works stable within recommended normal range –
see Figure 4. Long term exposures to conditions outside
normal range, especially at humidity >80%RH, may
temporarily offset the RH signal (+3 %RH after 60h). After
return to normal range it will slowly return towards
calibration state by itself. See Section 1.4 “Reconditioning
Procedure” to accelerate eliminating the offset. Prolonged
exposure to extreme conditions may accelerate ageing.
Figure 4: Operating Conditions
1.2
For maintain high accuracy specifications the sensor shall
not be soldered. Sockets may be used such as “Preci-dip /
Mill-Max R851-83-004-20-001” or similar.
Standard wave soldering ovens may be used at maximum
235°C for 20 seconds. For manual soldering contact time
must be limited to 5 seconds at up to 350°C
After wave soldering the devices should be stored at
>75%RH for at least 12h to allow the polymer to re-
hydrate. Alternatively the re-hydration process may be
performed at ambient conditions (>40%RH) during more
than 5 days.
In no case, neither after manual nor wave soldering, a
board wash shall be applied. In case of application with
exposure of the sensor to corrosive gases the soldering
pads of pins and PCB shall be sealed to prevent loose
contacts or short cuts.
1.3
It is of great importance to understand that a humidity
sensor is not a normal electronic component and needs to
be handled with care. Chemical vapors at high
concentration in combination with long exposure times
may offset the sensor reading.
7
235°C corresponds to 455°F, 350°C corresponds to 662°F
100
80
60
40
20
0
Operating Conditions
Sockets and Soldering
Storage Conditions and Handling Instructions
-40
-20
0
Normal
Range
Temperature (°C)
20
40
60
7
80
.
100
Version 4.3 – May 2010
120
For these reasons it is recommended to store the sensors
in original packaging including the sealed ESD bag at
following conditions: Temperature shall be in the range of
10°C – 50°C (0 – 80°C for limited time) and humidity at 20
– 60%RH (sensors that are not stored in ESD bags). For
sensors that have been removed from the original
packaging we recommend to store them in ESD bags
made of metal-in PE-HD
In manufacturing and transport the sensors shall be
prevented of high concentration of chemical solvents and
long exposure times. Out-gassing of glues, adhesive tapes
and stickers or out-gassing packaging material such as
bubble foils, foams, etc. shall be avoided. Manufacturing
area shall be well ventilated.
For more detailed information please consult the
document “Handling Instructions” or contact Sensirion.
1.4
As stated above extreme conditions or exposure to solvent
vapors may offset the sensor. The following reconditioning
procedure may bring the sensor back to calibration state:
Baking:
Re-Hydration:
1.5
Relative
temperature. Therefore, it is essential to keep humidity
sensors at the same temperature as the air of which the
relative humidity is to be measured. In case of testing or
qualification the reference sensor and test sensor must
show equal temperature to allow for comparing humidity
readings.
The packaging of SHT7x is designed for minimal heat
transfer from the pins to the sensor. Still, if the SHT7x
shares a PCB with electronic components that produce
heat it should be mounted in a way that prevents heat
transfer or keeps it as low as possible.
Furthermore, there are self-heating effects in case the
measurement frequency is too high. Please refer to
Section 3.3 for detailed information.
8
9
For example, 3M antistatic bag, product “1910” with zipper .
75%RH can conveniently be generated with saturated NaCl solution.
100 – 105°C correspond to 212 – 221°F, 20 – 30°C correspond to 68 – 86°F
Reconditioning Procedure
Temperature Effects
humidity
100 – 105°C at < 5%RH for 10h
20 – 30°C at ~ 75%RH for 12h
reading
8
.
strongly
depends
9
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3/11
on

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