Argon Gas Supply Calibration in Metal Powder Atomization
Precision calibration of argon mass flow and trace purity controls particle size distribution and prevents interstitial oxide formation in atomized powders.
Chilled Mirror Hygrometer
Meaning
Moisture measurement instrumentation that determines dew or frost point by cooling a reflective surface until condensation begins to form represents the primary reference standard for humidity calibration. The chilled mirror hygrometer utilizes a thermoelectric cooler to lower the mirror temperature while an optoelectronic system detects the onset of condensation. At the transition point, a feedback loop stabilizes the mirror temperature to maintain a constant thickness of dew.
This temperature equals the dew point of the gas being analyzed.
Temperature Measurement
Platinum resistance thermometers embedded directly beneath the reflective surface record the exact temperature of the condensation point. This arrangement minimizes thermal gradients between the mirror surface and the sensor. Accuracies of plus or minus zero point one degree Celsius are common with high quality instruments.
Contamination Risk
Soluble salts or particulate matter deposited on the reflective surface alter the vapor pressure of the condensing water. This contamination causes a drift in the measured dew point. Periodic cleaning of the mirror is necessary to maintain accuracy.
Some instruments use automated cycle routines to heat the mirror and burn off or redistribute contaminants.
Calibration Standard
Metrology laboratories use these devices to calibrate other humidity sensors due to their fundamental operating principle. The direct relationship between dew point temperature and water vapor pressure requires no secondary calibration curves. This makes the instrument a highly stable transfer standard.