Armored RTDs (Resistance Temperature Detectors) are temperature sensors that exploit the principle that a material’s electrical resistance changes predictably with temperature; they feature a compact, flexible design—smaller in diameter and more bendable than assembled platinum RTDs—making them ideal for installation in narrow pipelines or applications requiring fast response and miniaturization. Their structure comprises three main parts: the sensing element (platinum resistor with internal leads), high-purity magnesium oxide insulation between leads and between leads and sheath, and a seamless metal protective tube (typically stainless steel) enclosing both insulation and sensor, enabling robust, reliable temperature measurement with direct readout of resistance-to-temperature conversion by connected instrumentation.