chips ( Platinum Thin Film Elements ) are manufactured from metals whose resistance
increases with temperature. Within a limited temperature range, the resistivity
increases linearly with temperature. This resistance is directly proportional
to a metal wire's length, and inversely proportional to the cross-sectional area.
The element is coated with ceramic that can withstand high temperature. Some Rtd
are wire wounded with ceramic casing.
chemical stability, availability in pure form, and highly reproducible electrical
properties, has made Platinum the metal of choice for RTD's which are made of
either IEC/DIN grade platinum or reference-grade platinum. The difference lies
in the purity of the platinum. The IEC/DIN standard is pure platinum that is intentionally
contaminated with other platinum.
the resistance of an RTD, a small electric current (about 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.
The heating is proportional to the electric power (P=Isq X R) in the RTD and the
heat transfer between the RTD sensing element and the RTD environment. If the
RTD is in a poor heat transfer medium (e.g., air), it will heat up more than if
it is in a fluid, such as water. The electrical current will heat the sensor and
may influence the measurement.
RTD chips should meet the standards of JIS C 1604
and IEC751 Grade A or B.