The measurement of very low humidities of gases is an increasingly important problem, particularly in the microelectronics industry, where water is the most common contaminant of ultra pure gases. A residual water content of 1 ppb (dew point -112(C) is now demanded in some manufacturing processes, so reliable methods of measuring such low moisture levels are required. Especially at low dewpoints, state-of-the-art humidity sensors lack measurement accuracy, sensitivity and stability. They are also slow in responding to humidity changes, and hence are unsuitable for on-line process control. A mass spectrometer (APIMS) is the most reliable system for measuring low humidity, but is unsuitable as a transfer standard because of its geometrical dimensions and high cost. A cheaper, more readily transportable system could offer great advantages as a secondary transfer standard.
This project proposes to adapt advanced infrared absorption spectroscopy methods using FM-modulation techniques to detect very low humidities at atmospheric conditions. The absorption method permits very fast measurements, thus facilitating on-line process control provided equilibration of the apparatus is achieved with respect to trace quantities of water. The resulting instrument would be valuable for national standards laboratories and industrial laboratories throughout the European Union for the reliable measurement of humidities at very low levels. There is currently no recognized standard below a dewpoint of about -80 (C, but the instrument could assist the development of an international transfer standard with traceability of the measurement through accredited laboratories. To develop the infrared absorption humidity sensor, an international team of 6 partners and 2 subcontractors has been brought together.
The partnership includes a university and a national standards laboratory which will together undertake the actual development work. Major tasks are the test and selection of a suitable frequency modulated diode laser and low-noise detector, as well as the design of a measuring cell, with all associated electronics and software. Four national standards laboratories will test the instrument and assess its performance against established techniques, with a view to the traceability of the measurement. An industrial partner interested in gas purification down to impurity levels better than 1 ppb will also assist in the assessment of the instrument and establishing appropriate specifications.
Funding SchemeCSC - Cost-sharing contracts
2600 AR Delft
TW11 0LW Teddington
20020 Lainate Milano