TMP35_10 Datasheet, PDF (12/20 Pages) Analog Devices – Low Voltage Temperature Sensors

TMP35/TMP36/TMP37
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 TMP3x 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.
TMP3x
R1
300kΩ
TMP3x
R2
300kΩ
TMP3x
R3
300kΩ
R4
7.5kΩ
2.7V < +V_S < 5.5V
0.1µF
7
2
–
6
OP193
3
+
4
V_TEMP(AVG)
@ 10mV/°C FOR TMP35/TMP36
@ 20mV/°C FOR TMP37
R5
100kΩ
R6
7.5kΩ
FOR R1 = R2 = R3 = R;
V_TEMP(AVG) = 1 (TMP3x₁ + TMP3x₂ + TMP3x₃)
3
R5 = ^R1
3
R4 = R6
Figure 28. Configuring Multiple Sensors for
Average Temperature Measurements
2.7V < +V_S < 5.5V
0.1µF
TMP36
R1¹
R2¹
@ T1
R8
25kΩ
0.1µF
TMP36
@ T2
0.1µF
R3¹
R9
25kΩ
7
2–
OP193
6
3
+
4
CENTERED AT
R4¹
1µF
V_OUT
R7
100kΩ
0°C ≤ T_A ≤ 125°C
R5
100kΩ
R6
100kΩ
V_OUT = T2 – T1 @ 10mV/°C
CENTERED AT
V_S
2
NOTE:
1 _{R1–R4, CADDOCK T914–100k–100, OR EQUIVALENT.}
Figure 29. Configuring Multiple Sensors for
Differential Temperature Measurements
Rev. F | Page 12 of 20