Datasheet
TMP35/TMP36/TMP37 Data Sheet
AVERAGE AND DIFFERENTIAL TEMPERATURE
MEASUREMENT
In many commercial and industrial environments, temperature
sensors often measure the average temperature in a building, or
the difference in temperature between two locations on a factory
floor or in an industrial process. The circuits in Figure 28 and
Figure 29 demonstrate an inexpensive approach to average and
differential temperature measurement.
In Figure 28, an OP193 sums the outputs of three temperature
sensors to produce an output voltage scaled by 10 mV/°C that
represents the average temperature at three locations. The circuit
can be extended to include as many temperature sensors as
required as long as the transfer equation of the circuit is
maintained. In this application, it is recommended that one
temperature sensor type be used throughout the circuit;
otherwise, the output voltage of the circuit cannot produce an
accurate reading of the various ambient conditions.
The circuit in Figure 29 illustrates how a pair of TMP35/TMP36/
TMP37 sensors used with an OP193 configured as a difference
amplifier can read the difference in temperature between two
locations. In these applications, it is always possible that one
temperature sensor is reading a temperature below that of the
other sensor. To accommodate this condition, the output of the
OP193 is offset to a voltage at one-half the supply via R5 and
R6. Thus, the output voltage of the circuit is measured relative
to this point, as shown in Figure 29. Using the TMP36, the
output voltage of the circuit is scaled by 10 mV/°C. To minimize
the error in the difference between the two measured
temperatures, a common, readily available thin-film resistor
network is used for R1 to R4.
OP193
0.1µF
2
3
4
6
7
V
TEMP(AVG)
@ 10mV/°C FOR TMP35/TMP36
@ 20mV/°C FOR TMP37
2.7V < +V
S
< 5.5V
FOR R1 = R2 = R3 = R;
V
TEMP(AVG)
= 1 (TMP3x
1
+ TMP3x
2
+ TMP3x
3
)
3
R1
300kΩ
R2
300kΩ
R3
300kΩ
R4
7.5kΩ
R1
3
R4 = R6
R6
7.5kΩ
R5
100kΩ
R5 =
TMP3x
TMP3x
TMP3x
–
+
00337-026
Figure 28. Configuring Multiple Sensors for
Average Temperature Measurements
TMP36
@ T1
0.1µF
0.1µF
2
3
4
6
7
OP193
1µF
V
OUT
R3
1
R4
1
R2
1
R1
1
2.7V < +V
S
< 5.5V
TMP36
@ T2
R5
100kΩ
R6
100kΩ
V
OUT
= T2 – T1 @ 10mV/°C
V
S
2
NOTE:
1
R1–R4, CADDOCK T914–100k–100, OR EQUIVALENT.
0.1µF
R7
100kΩ
R8
25kΩ
R9
25kΩ
0°C ≤ T
A
≤ 125°C
CENTERED AT
CENTERED AT
–
+
00337-027
Figure 29. Configuring Multiple Sensors for
Differential Temperature Measurements
Rev. H | Page 12 of 19
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