AD590(2003) Просмотр технического описания (PDF) - Analog Devices

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AD590
(Rev.:2003)

Two-Terminal IC Temperature Transducer

Analog Devices 

AD590

GENERAL APPLICATIONS

Figure 14 demonstrates the use of a low cost digital panel meter

for the display of temperature on either the Kelvin, Celsius, or

Fahrenheit scales. For Kelvin temperature, Pins 9, 4, and 2 are

grounded; for Fahrenheit temperature, Pins 4 and 2 are left

open.

5V

6

8

9

+

AD590

–

AD2040

4

5

3

2

OFFSET

CALIBRATION

GAIN

SCALING

OFFSET

SCALING

GND

Figure 14. Variable Scale Display

The above configuration yields a 3-digit display with 1°C or 1°F

resolution, in addition to an absolute accuracy of ±2.0°C over

the −55°C to +125°C temperature range, if a one-temperature

calibration is performed on an AD590K, AD590L, or AD590M.

Connecting several AD590 units in series as shown in Figure 15

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.

15V

10kΩ

(0.1%)

+

AD590

–

+

AD590

–

+

AD590

–

+

VT MIN

–

5V

+

+

–

–

+

AD590

–

333.3Ω

(0.1%)

+

VT AVG

–

Figure 15. Series and Parallel Connection

The circuit in Figure 16 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

sensors in applications such as fluid-level detectors or

anemometry.

+

AD590L

– #2

V+

R3

10kΩ

+

AD590L

– #1

R2

50kΩ

R1

5MΩ

R4

10kΩ

–

AD707A

+

(T1 – T2) × (10mV/°C)

V–

Figure 16. Differential Measurements

Figure 17 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 ambient temperatures

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 TCs as specified in Figure 17,

compensation accuracy is within ±0.5°C for circuit

temperatures between 15°C and 35°C. Other thermocouple

types can be accommodated with different resistor values. Note

that the TCs of the voltage reference and the resistors are the

primary contributors to error.

7.5V

+ AD580

– VOUT

+

AD590

–

52.3Ω

8.66kΩ

RT

1kΩ

REFERENCE

JUNCTION

+

–

CU

+–

METER

IRON

CONSTANTAN

MEASURING

JUNCTION

RESISTORS ARE 1%, 50PPM/°C

Figure 17. Cold Junction Compensation Circuit for Type J Thermocouple

Figure 18 is an example of a current transmitter designed to be

used with 40 V, 1 kΩ systems; it uses its full current range of

4 mA to 20 mA for a narrow span of measured temperatures. In

this example, the 1 µA/K output of the AD590 is amplified to

1 mA/°C and offset so that 4 mA is equivalent to 17°C and

20 mA is equivalent to 33°C. RT is trimmed for proper reading

at an intermediate reference temperature. With a suitable choice

of resistors, any temperature range within the operating limits

of the AD590 may be chosen.

Rev. C | Page 10 of 16

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