Datasheet SHT7x
www.sensirion.com
Version 4.1 – July 2008
7/11
Figure 12: Example RH measurement sequence for value “0000’1001“0011’0001” = 2353 = 75.79 %RH (without temperature
compensation). DATA valid times are given and referenced in boxes on DATA line. Bold DATA lines are controlled by sensor while plain
lines are controlled by the micro-controller.
Bit Type Description
Default
7
reserved
0
6 R
End of Battery (low voltage
detection)
‘0’ for VDD > 2.47
‘1’ for VDD < 2.47
X
No default value,
bit is only updated
after a
measurement
5
reserved
0
4
reserved
0
3
For Testing only, do not use
0
2 R/W
Heater
0 off
1 R/W
no reload from OTP
0 reload
0 R/W
’1’ = 8bit RH / 12bit Temp.
resolution
’0’ = 12bit RH / 14bit Temp.
resolution
0
12bit RH
14bit Temp.
Table 5: Status Register Bits
Measurement resolution: The default measurement
resolution of 14bit (temperature) and 12bit (humidity) can
be reduced to 12 and 8bit. This is especially useful in high
speed or extreme low power applications.
End of Battery function detects and notifies VDD voltages
below 2.47 V. Accuracy is
±0.05 V.
Heater: An on chip heating element can be addressed by
writing a command into status register. The heater may
increase the temperature of the sensor by 5 – 10°C12
beyond ambient temperature. The heater draws roughly
8mA @ 5V supply voltage.
12 Corresponds to 9 – 18°F
For example the heater can be helpful for functionality
analysis: Humidity and temperature readings before and
after applying the heater are compared. Temperature shall
increase while relative humidity decreases at the same
time. Dew point shall remain the same.
Please note: The temperature reading will display the
temperature of the heated sensor element and not
ambient temperature. Furthermore, the sensor is not
qualified for continuous application of the heater.
4 Conversion of Signal Output
4.1
Relative Humidity
For compensating non-linearity of the humidity sensor –
see Figure 13 – and for obtaining the full accuracy of the
sensor it is recommended to convert the humidity readout
(SORH) with the following formula with coefficients given in
Table 6:
2
RH
3
RH
2
1
linear
SO
c
SO
c
c
RH
⋅
+
⋅
+
=
(%RH)
SORH
c1
c2
c3
12 bit
-2.0468
0.0367
-1.5955E-6
8 bit
-2.0468
0.5872
-4.0845E-4
Table 6: Optimized V4 humidity conversion coefficients
The values given in Table 6 are newly introduced and
provide optimized accuracy for V4 sensors along the full
measurement range. The parameter set cx*, which has
been proposed in earlier datasheets, which was optimized
DATA
DATA
SCK
SCK
SCK
DATA
A2
A1
A0
C4
C3
C2
C1
C0
ACK
15
14
13
12
11
10
9
8
ACK
7
6
5
4
3
2
1
0
ACK
7
6
5
4
3
2
1
0
ACK
Transmission Start
Address = ‘000’
Command = ‘00101’
12bit Humidity Data
CRC-8 Checksum
Transmission Start
Measurement (80ms for 12bit)
Sleep (wait for next
measurement)
Idle Bits
Skip ACK to end trans-
mission (if no CRC is used)
Skip ACK to end transmission
Sensor pulls DATA line low after
completion of measurement
MSb
LSb
MSb
LSb
15
14
13
12
11
10
9
8
ACK
7
6
5
4
3
2
1
0
ACK
A2
A1
A0
C4
C3
C2
C1
C0
ACK
7
6
5
4
3
2
1
0
ACK
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