AD590
Data Sheet
GENERAL APPLICATIONS
V+
Figure 17 shows a typical use of the AD590 in a remote
temperature sensing application. The AD590 is used as a
thermometer circuit that measures temperature from −55°C to
+150°C, with an output voltage of 1 mV/°K. Because the
AD590 measures absolute temperature (its nominal output is
1 mA/K), the output must be offset by 273.2 mA to read out in
degrees Celsius.
R3
10kΩ
+
–
AD590L
#2
–
+
OP177
+
–
R1
5MΩ
AD590L
#1
(T1 – T2) × (10mV/°C)
R2
50kΩ
R4
10kΩ
V–
+
I
T
AD590
7V
Figure 19. Differential Measurements
–
Figure 20 is an example of a cold junction compensation circuit
for a Type J thermocouple using the AD590 to monitor the
reference junction temperature. This circuit replaces an ice-bath
as the thermocouple reference for ambienttemperatures
between 15°C and 35°C. The circuit is calibrated by adjusting RT
for a proper meter reading with the measuring junction at a
known reference temperature and the circuit near 25°C. Using
components with the TCsas specified in Figure 20, compensation
accuracy is within 0.5°C for circuit temperatures between 15°C
and 35°C. Otherthermocouple typescan be accommodated with
different resistor values. Note thatthe TCs of the voltage
reference and the resistors are the primary contributors to error.
I
T
I
T
1k
0.1% LOW
TCR RESISTOR
1mV/k
Figure 17. Variable Scale Display
Connecting several AD590 units in series, as shown in Figure 18,
allows the minimum of all the sensed temperatures to be
indicated. In contrast, using the sensors in parallel yields the
average of the sensed temperatures.
7.5V
IRON
REFERENCE
JUNCTION
15V
+
+
CONSTANTAN
AD590
AD590
–
–
5V
+
–
+
+
–
+
–
+
AD590
–
AD580
C
AD590
–
+
–
U
+
52.3Ω
MEASURING
JUNCTION
+
V
AD590
–
OUT
–
8.66kΩ
+
+
10kΩ
(0.1%)
333.3Ω
(0.1%)
METER
V
MIN
V AVG
T
T
R
T
–
–
1kΩ
RESISTORS ARE 1%, 50ppm/°C
Figure 18. Series and Parallel Connection
Figure 20. Cold Junction Compensation Circuit for Type J Thermocouple
The circuit in Figure 19 demonstrates one method by which
differential temperature measurements can be made. R1 and R2
can be used to trim the output of the op amp to indicate a
desired temperature difference. For example, the inherent offset
between the two devices can be trimmed in. If V+ and V− are
radically different, then the difference in internal dissipation
causes a differential internal temperature rise. This effect can be
used to measure the ambient thermal resistance seen by the
sensorsin applications such asfluid-level detectors oranemometry.
Rev. G | Page 10 of 16
ADI [ ADI ]
