ENTC-370PROF. ALVARADO1 THERMODYNAMICS LAB: Temperature Measurement ENTC - 370

PROF. ALVARADO2 Temperature Sensors Contact Sensors: –Thermocouples (two wires made of different materials) –RTDs (Resistance Temperature Detector) –Thermistors (semiconductor) –Thermometers (mercury expansion) –ICs and Diode Non-Contact Sensors: –IR Thermometers (Infrared Temperature Probe)

ENTC-370PROF. ALVARADO3 Thermocouples A thermocouple consists of two wires of different materials joined together. The metals responded differently to the temperature difference, creating a current loop and a magnetic field. When the temperature at the junction is different from a reference temperature, the Seebeck effect is generated.

ENTC-370PROF. ALVARADO4 Thermocouples Types Thermocouples are classified based on the materials of the wires. The most common thermocouple types are: –Type J: Iron-Constantan –Type T: Copper-Constantan –Type K: Chromel-Alumel –Type E: Chromel, Constantan –Type N:Nicosil, Nisil –Type R:Platinum-6% Rhodium, Platinum – 13% Rhodium –Type S:Platinum, Platinum- 10% Rodium The first element is the positive element The negative wire is color coded red.

ENTC-370PROF. ALVARADO5 Thermocouples Types Composition of Thermocouples alloys: –Alumel: 94% nickel, 3% manganese, 2% aluminum, 1% silicon –Chromel: 90% nickel, 10% chromium –Constantan: 55% copper, 45% nickel –Nicosil: 84% nickel, 14% chromium, 1.5% silicon Another classification is based on calibration accuracy: –Precision –Standard –Lead-wire

ENTC-370PROF. ALVARADO6 Thermocouples Limits

ENTC-370PROF. ALVARADO7 Thermocouple Errors Type Thermocouple Error, Standard Grade Error, Special Grade E 1.7 C or 0.5% above 0 C 1.0 C or 0.4% J 2.2 C or 0.75%above 0 C 1.1 C or 0.4% K 2.2 C or 0.75%above 0 C 1.1 C or 0.4% N 2.2 C or 0.75%above 0 C 1.1 C or 0.4% R 1.5 C or 0.25%0.6 C or 0.1% S 1.5 C or 0.25%0.6 C or 0.1% T 1.0 C or 0.75% above 0 C 0.5 C or 0.4%

ENTC-370PROF. ALVARADO8 Thermocouple Basic Circuit Ice Bath Electronically Controlled Reference Compensated Reference Temperature Systems Zone boxes

ENTC-370PROF. ALVARADO9 References Notes on using thermocouples, Dr. Robert Moffat, Electronics – Cooling, Jan. 97. Experimental methods for engineers, Holman J., 7 th. Edition, 2000