What is a Thermocouple ?
RTDs are completely passive sensing elements, requiring the application of an externally-sourced electric current in order to function as temperature sensors. Thermocouples, however, generate their own electric potential. In some…
RTD Sensor Connections
Proper connections for all three types of RTD sensor (2-wire, 3-wire, and 4-wire) to a user configurable transmitter are shown in the following illustrations: It is critically important to note…
What is a Three-wire RTD ?
A compromise between two-wire and four-wire RTD connections is the three-wire connection, which looks like this: In a three-wire RTD circuit, voltmeter “A” measures the voltage dropped across the RTD…
What is a Four-wire RTD ?
A very old electrical measurement technique known as the Kelvin or four-wire method is a practical solution to the problem of wire resistance. Commonly employed to make precise resistance measurements…
Temperature Coefficient of Resistance (α)
A Resistive Temperature Detector (RTD) is a special temperature-sensing element made of fine metal wire, the electrical resistance of which changes with temperature as approximated by the following formula: Where,…
Filled-bulb Temperature Sensors
Filled-bulb systems exploit the principle of fluid expansion to measure temperature. If a fluid is enclosed in a sealed system and then heated, the molecules in that fluid will exert…
Bi-metal Temperature Sensors
Solids tend to expand when heated. The amount that a solid sample will expand with increased temperature depends on the size of the sample, the material it is made of,…
Stilling Wells for Level Measurement
Disturbances in the liquid tend to complicate liquid level measurement. These disturbances may result from liquid introduced into a vessel above the liquid level (splashing into the liquid’s surface), the…
Radiation Level Measurement
Certain types of nuclear radiation easily penetrates the walls of industrial vessels, but is attenuated by traveling through the bulk of material stored within those vessels. By placing a radioactive…
Magnetostrictive Level Measurement
A variation on the theme of echo-based level instruments, where the level of some process material in a vessel is measured by timing the travel of a wave between the…
