Measurements, Instrumentation & Controls

The Seebeck effect: a junction of two dissimilar metals generates a small voltage (EMF) that varies with the temperature difference between the measuring junction and the reference junction.

Because a thermocouple produces voltage proportional to the temperature DIFFERENCE between junctions; the absolute hot-junction temperature can only be found if the reference junction temperature is known (cold-junction compensation).

An RTD relies on the predictable, nearly linear increase of a metal's electrical resistance (commonly platinum, e.g., Pt100) with temperature.

A strain gauge measures mechanical strain via change in electrical resistance. Gauge factor GF = (ΔR/R)/ε, the ratio of fractional resistance change to strain (typically about 2 for metallic gauges).

Because the fractional resistance change ΔR/R is very small; a Wheatstone bridge converts that tiny change into a measurable voltage and can compensate for temperature effects.

Strain-gauge (diaphragm with bonded gauges), piezoresistive (silicon), capacitive (diaphragm changes capacitance), and piezoelectric (for dynamic pressures) are common pressure sensing methods.