The development of a direct reading relative humidity instrument

The first objective of this problem - thorough literature review - was conducted on all available references concerning humidity measurement, and visits were made to the American Instrument Company in Silver Springs, Maryland, and the National Bureau of Standards. The survey evaluated the instruments in use today and also explored many of the ideas and concepts that have been suggested in past years as possible means for humidity measurement. A summation of the survey indicated that the electric hygrometer with a ceramic element was a good basic theory for a humidity instrument, but still required development before it,would be of any practical use. The second objective - development of a useful hygrometer - was directed towards the development of the electric hygrometer using a ceramic element. The study that resulted included the evaluation of two methods for determining the change of resistance of the ceramic element, as well as a preliminary investigation of the characteristics of a ceramic element when employed as the sensing element for an electric hygrometer. The element intended for the initial tests, a porous ceramic containing mostly aluminum oxide, was the only material tested, but the tests included elements of the pure ceramic material and the same material after it was soaked in a saturated solution of lithium chloride. With the instruments used, the indications were that both elements were suited for determining the high humidities. The pure element had a lower limit of 50 percent relative humidity, and the coated element a lower limit of 20 percent. Two instruments were used for indicating the change of relative humidity. A vacuum tube voltmeter type instrument was tested, but found unsatisfactory due to variations of readings under the same conditions, drifting of the zero set, and excessive fluctuations of the indicating meter. The other instrument or method used was to apply an A-C voltage across the element, and to measure the resulting current flow. Because the current was maintained above 1 milliampere, heating of the element was caused, resulting in a change of element resistance. However, results with this instrument were sufficient to establish a calibration curve for the apparatus. A comparison of this device and a psychrometer indicated the usefulness of such an instrument, but confirmed that the development was not complete. The overall result of the research indicates that the selection of the ceramic sensing element for an electric hygrometer has merit, but more development is necessary. Two phases of any future work on the problem should be the development of the indicating instrument, and the selection and design of the sensing element. The need for a satisfactory instrument still exists, and the successful development of the type instrument described herein, would undoubtedly meet the requirements.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Agricultural Engineering

Department dc:contributor.department

Agricultural Engineering

Grantor dc:publisher

Virginia Polytechnic Institute

Year dc:date.issued

1956

Author dc:creator

• Mason, John Philip Hanson

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/52201

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/52201