A Calibration Facility for Dew Point in Air up to 1 MPa

• Published in: International journal of thermophysics 2015-12, Vol.36 (12), p.3453-3465
• Main Authors: Carroll, P. A., Bell, S. A., Stevens, M.
• Format: Article
• Language: English
• Subjects: Barometric pressure; Calibration; Classical Mechanics; Condensed Matter Physics; Confidence; Dew point; Humidity; Humidity measurement; Hygrometers; Industrial Chemistry/Chemical Engineering; Physical Chemistry; Physics; Physics and Astronomy
• ISSN: 0195-928X; 1572-9567
• DOI: 10.1007/s10765-015-1984-2

The provision of primary dew-point standards for humidified air and nitrogen at atmospheric pressure is well established, and measurement traceability to these standards provides confidence in a vast number of air humidity measurements. However, hygrometers are used industrially at a wide range of pressures. Both the performance of hygrometers and the properties of humid gases are known to vary with gas pressure. The pressure-dependence of gas non-ideality for air–water mixtures (water-vapor enhancement factor) is well enough known at moderate pressures, but there remains a need to characterize hygrometers at the pressure of use. To address this, a humidity calibration capability of wider scope is under development at the UK National Physical Laboratory (NPL). As an initial stage in the development of this capability, a humidity standard generating air or nitrogen in the dew-point range from - 60 ∘ C to + 10 ∘ C , at pressures up to 1 MPa (10 bar) has been validated for the calibration of hygrometers. The expanded uncertainty of the dew-point generator in this range with a coverage factor k = 2 is ± 0.07 ∘ C .