Thermistor Signal Conditioning in Subsea Data Logging Systems
Pulsed ratiometric excitation and ultra-low tempco references eliminate subsea thermistor self-heating and hydrostatic drift down to millikelvin accuracy.
Triple Point Cell
Meaning
Laboratory calibration instruments that maintain a substance at its solid, liquid, and gas phases simultaneously provide highly reproducible temperature references. The triple point cell is the primary method for realizing the most essential reference point on the ITS-90 scale. Its use is limited to specialized metrology laboratories due to the complex procedures required to establish and maintain the three-phase equilibrium.
Calibration Reference
Water is the most common substance used in these cells, providing a reference temperature of exactly point-zero-one degrees Celsius. This temperature is used to calibrate high-precision standard platinum resistance thermometers.
Operational Realization
Creating the triple point requires freezing a mantle of ice around an internal well while maintaining a liquid water layer next to the glass wall. The thermometer to be calibrated is inserted into this well, where it is surrounded by the three phases in equilibrium. The cell must be kept in a temperature-controlled bath to prolong the life of the ice mantle, preventing it from melting during measurements.
Longterm Stability
Once established, the triple point temperature remains stable to within a fraction of a millikelvin for several weeks. This stability allows laboratories to perform multiple calibrations without resetting the cell. It ensures the high level of traceability required for global climate and oceanographic datasets.