Reference Instrument
Metrological devices realize temperature values with the highest achievable repeatability between the triple point of water and the freezing point of silver. The standard platinum resistance thermometer utilizes a high-purity coil of platinum to detect changes in electrical resistance. This sensor serves as the primary transfer standard for temperature worldwide.
Interpolation Curve
Mathematical equations defined by the International Temperature Scale convert the raw resistance into a precise numerical value. Using a standard platinum resistance thermometer allows laboratories to achieve an uncertainty of less than one millikelvin in controlled baths. Any mechanical shock to the ceramic frame changes the resistance and ruins the calibration.
Thermal Shunt
Construction features include quartz or sapphire insulators that prevent leakage currents from distorting the signal at high heat. Inside the standard platinum resistance thermometer the lead wires are carefully designed to minimize heat conduction from the tip to the terminal. Engineers handle these sensors with extreme care to maintain their specific crystal structure.
Limit Control
Verification involves checking the value of the sensor at the triple point of water every few uses. If the standard platinum resistance thermometer drifts by more than the allowed range it is sent for annealing to remove strain. These sensors are far too fragile for ordinary industrial applications.
