Thermocouple amplifiers

18 August 2010 Analogue, Mixed Signal, LSI

Analog Devices has introduced a series of precision thermocouple amplifiers for K- and J-type thermocouples, which are widely used to measure temperature in industrial, commercial and scientific applications.

Thermocouple systems provide accurate and reliable temperature measurements and control, are cost-effective, and can measure a wide range of temperatures. However, to achieve good measurement performance, cold junction compensation and a high gain accuracy precision amplifier are required. Analog Devices’ AD8494, AD8495, AD8496 and AD8497 thermocouple amplifiers address this issue by featuring on-chip cold junction compensation that automatically adjusts the thermocouple output for changes in ambient temperature.

The four new devices each convert the small voltages generated by a thermocouple junction into a 5 mV/°C analog signal that can be read by an ADC (analog-to-digital converter) or microcontroller. The integrated cold junction compensation ensures accurate measurement over a wide range of ambient temperatures while the high common-mode rejection (0,1°C/V) allows the AD849x to reject common-mode noise that may be associated with long-lead thermocouples.

The AD849x thermocouple amplifiers operate off a wide variety of voltages, from single 2,7 V to dual ±18 V supplies and are very power efficient, consuming only 180 μA quiescent supply current. In single-supply operation, the amplifiers can directly interface to lower-supply ADCs while higher, dual-supply voltages can be used for industrial systems that require a wide common mode input range. With a single 5 V supply, the amplifiers can cover nearly 1000° of a thermocouple’s temperature range. A reference pin allows for level shifting of the 0°C output so that negative temperatures can be measured, even on a single supply.

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