Datasheet

ADC

PRESSURE

SENSOR

100:

2.4 k:

LMV852

OUT

LMV851, LMV852, LMV854

www.ti.com

SNOSAW1A –OCTOBER 2007–REVISED MARCH 2013

Figure 55. Pressure Sensor Application

THERMOCOUPLE AMPLIFIER

The following circuit is a typical example for a thermocouple amplifier application using an LMV851/LMV852, or

LMV854. A thermocouple converts a temperature into a voltage. This signal is then amplified by the

LMV851/LMV852, or LMV854. An ADC can convert the amplified signal to a digital signal. For further processing

the digital signal can be processed by a microprocessor and used to display or log the temperature. The

temperature data can for instance be used in a fabrication process.

Characteristics of a Thermocouple

A thermocouple is a junction of two different metals. These metals produce a small voltage that increases with

temperature.

The thermocouple used in this application is a K-type thermocouple. A K-type thermocouple is a junction

between Nickel-Chromium and Nickel-Aluminum. This is one of the most commonly used thermocouples. There

are several reasons for using the K-type thermocouple, these include: temperature range, the linearity, the

sensitivity, and the cost.

A K-type thermocouple has a wide temperature range. The range of this thermocouple is from approximately

−200°C to approximately 1200°C, as can be seen in Figure 56. This covers the generally used temperature

ranges.

Over the main part of the temperature range the output voltage depends linearly on the temperature. This is

important for easily converting the measured signal levels to a temperature reading.

The K-type thermocouple has good sensitivity when compared to many other types; the sensitivity is about 41

uV/°C. Lower sensitivity requires more gain and makes the application more sensitive to noise.

In addition, a K-type thermocouple is not expensive, many other thermocouples consist of more expensive

materials or are more difficult to produce.

Product Folder Links: LMV851 LMV852 LMV854