TMP35/TMP36/TMP37

Rev. F | Page 12 of 20

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.

OP193

0.1µF

2

3

4

6

7

@ 10mV/°C FOR TMP35/TMP36

@ 20mV/°C FOR TMP37

FOR R1 = R2 = R3 = R;

3

R1

300kΩ

R2

300kΩ

R3

300kΩ

R4

7.5kΩ

R1

3

R4 = R6

R6

7.5kΩ

R5

100kΩ

R5 =

TMP3x

TMP3x

TMP3x

–

+

Figure 28. Configuring Multiple Sensors for

Average Temperature Measurements

TMP36

@ T1

0.1µF

0.1µF

2

3

4

6

7

OP193

1µF

TMP36

@ T2

R5

100kΩ

R6

100kΩ

2

NOTE:

0.1µF

R7

100kΩ

R8

25kΩ

R9

25kΩ

CENTERED AT

CENTERED AT

–

+

Figure 29. Configuring Multiple Sensors for

Differential Temperature Measurements