"chromel" - 1 õppematerjal

Book Analog Interfacing to Embedded Microprocessors

2% Nickel and nickel/iron: .5% Aside from better tolerance and overall lower resistance, the interface to an RTD is similar to that for a thermistor. Thermocouples A thermocouple is made by joining two dissimilar metals. Thomas Seebeck discovered in 1821 that when such a junction is heated, it generates a tiny voltage. The amount of voltage is dependent on which two metals are joined. Three common thermocouple combinations are Iron-Constantan (Type J), Copper-Constantan (Type T), and Chromel-Alumel (Type K). The voltage produced by a thermocouple junction is very small, typically only a few millivolts. A type K thermocouple changes only about 40 mv per °C change in temperature; to measure temperature with .1°C accuracy, the mea- surement system must be able to measure a 4 mv change. Since any two dissimilar metals will produce a thermocouple junction when joined, the connection point of the thermocouple to the measurement system