The basics don’t change much “’Sensing elements themselves are pretty stable in that they don’t tend to change,’ says Paul Gobeille, Stellar senior automation engineer. “For example, you’ll find that the theories behind thermocouples (T/Cs), RTDs (resistance temperature detectors), thermistors and infrared (IR) sensors presented in various sources are virtually the same as when they…
Mechanical (liquid-in-glass thermometers, bimetallic strips, bulb & capillary, pressure type etc.) Thermojunctive (thermocouples) Thermoresistive (RTDs and thermistors) Radiative (infrared and optical pyrometers) Mechanical Temperature Measuring devices Principle of Operation A change in temperature causes some kind of mechanical motion, typically due to the fact that most materials expand with a rise in temperature. Mechanical thermometers can be…
THERMOCOUPLES A thermocouple is made up of two dissimilar metals, joined together at one end, that produce a voltage (expressed in millivolts) with a change in temperature. The junction of the two metals, called the sensing junction, is connected to extension wires. Any two dissimilar metals may be used to make a thermocouple. Principle of…
1 mA) must flow through the sensor to create the necessary voltage drop. The current causes the platinum element in the RTD to heat up above the temperature of the RTD’s environment (Also called Joule heating). The heating is proportional to the electric power (P = I2 R) in the RTD and the heat transfer between the RTD sensing…
types of thermocouples are the Type B, E, J, K, N, R, S, T, C, & P. Before choosing the type of thermocouple for your process, make sure you are aware of the limitations of all available calibration types. Type B Thermocouple The Type B thermocouple is composed of a platinum-30% rhodium (+) wire versus a platinum-6%…
Resistance Temperature Detector (RTD) is a temperature sensor which measures temperature using the principle that the resistance of a metal changes with temperature. In practice, an electrical current is transmitted through a piece of metal (the RTD element or resistor) located in proximity to the area where temperature is to be measured. The resistance value of…
This particular design has a platinum element that is surrounded by a porcelain insulator. The insulator prevents a short circuit between the wire and the metal sheath. Inconel, a nickel-iron-chromium alloy, is normally used in manufacturing the RTD sheath because of its inherent corrosion resistance. When placed in a liquid or gas medium, the Inconel sheath quickly…
Types of Thermocouples with Temperature Ranges & Color Codes Thermocouple can be defined as a sensor or device which is used for sensing or measuring temperature. The thermocouples are consisting of two metals or wires and the metals are known as legs. Both legs are welded together so as to create two junctions. Temperature is measured in these junctions…
