FUNCTIONAL BLOCK DIAGRAM

REV. B

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otherwise under any patent or patent rights of Analog Devices.

a

Thermocouple Conditioner and

Setpoint Controller

AD596*/AD597*

FEATURES

Low Cost

Operates with Type J (AD596) or Type K (AD597)

Thermocouples

Built-In Ice Point Compensation

Temperature Proportional Operation – 10 mV/ C

Temperature Setpoint Operation – ON/OFF

Programmable Switching Hysteresis

High Impedance Differential Input

GENERAL DESCRIPTION

The AD596/AD597 is a monolithic temperature setpoint con-

troller that has been optimized for use at elevated temperatures

such as those found in oven control applications. The device

cold junction compensates and amplifies a type J or K thermo-

couple input to derive an internal signal proportional to tem-

perature. The internal signal is then compared with an externally

applied setpoint voltage to yield a low impedance switched output

voltage. Dead-Band or switching hysteresis can be programmed

using a single external resistor. Alternately, the AD596/AD597 can

be configured to provide a voltage output (10 mV/

°C) directly from

a type J or K thermocouple signal. It can also be used as a stand-

alone voltage output temperature sensor.

The AD596/AD597 can be powered with a single supply from

+5 V to +30 V, or dual supplies up to a total span of 36 V.

Typical quiescent supply current is 160

µA, which minimizes

self-heating errors.

The AD596/AD597 H package option includes a thermocouple

failure alarm that indicates an open thermocouple lead when

operated in the temperature proportional measurement mode.

The alarm output has a flexible format which can be used to

drive relays, LEDs or TTL logic.

The device is packaged in a reliability qualified, cost effective

10-pin metal can or SOIC and is trimmed to operate over an

ambient temperature range from +25

°C to +100°C. Operation

over an extended ambient temperature range is possible with

slightly reduced accuracy. The AD596 will amplify thermo-

couple signals covering the entire –200

°C to +760°C tempera-

ture range recommended for type J thermocouples while the

AD597 can accommodate –200

°C to +1250°C type K inputs.

The AD596/AD597 has a calibration accuracy of

±4°C at an

ambient temperature of 60

°C and an ambient temperature

stability specification of 0.05

°C/°C from +25°C to +100°C. If

higher accuracy, or a lower ambient operating temperature is

required, either the AD594 (J thermocouple) or AD595 (K

thermocouple) should be considered.

*Protected by U.S. Patent No. 4,029,974.

PRODUCT HIGHLIGHTS

1. The AD596/AD597 provides cold junction compensation

and a high gain amplifier which can be used as a setpoint

comparator.

2. The input stage of the AD596/AD597 is a high quality in-

strumentation amplifier that allows the thermocouple to float

over most of the supply voltage range.

3. Linearization not required for thermocouple temperatures

close to 175

°C (+100°C to +540°C for AD596).

4. Cold junction compensation is optimized for ambient tem-

peratures ranging from +25

°C to +100°C.

5. In the stand-alone mode, the AD596/AD597 produces an

output voltage that indicates its own temperature.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 1998

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