Ambient Air quality Monitoring Guidlines. - Maharashtra Pollution ...

2. MEASUREMENT OF METEOROLOGICAL PARAMETERS
1.0 TITLE
Method for measurement of Meteorological Parameters.
2.0 PURPOSE
The purpose is to lay down an uniform and reliable method for measurement of
meteorological parameters in ambient air (humidity, temperature, wind speed,
wind direction).
3.0 PROCEDURE INSTRUCTIONS
Procedure instruction like, general information, set-up of the instrument, technical
information (data), installation of the instrument, maintenance of the system and
circuit diagram etc. is depicted in diagram I.
3.1 Meteorological Parameters
3.1.1 Humidity
(i) General Information - The water vapour in our air is called humidity. Since, in
general, air is only partially saturated with water vapour, it is of great interest to
determine the relative degree of saturation which is given in percent of maximum
humidity. For many institutions such as hospitals, EDP rooms, meteorological
measuring stations, museums, warehouses, green-houses etc., the exact
knowledge and constant monitoring of the relative humidity is of great
importance.
The hygro-transmitter, employed for such measurements, measures the relative
humidity, displays the data and simultaneously provides an electrical signal.
(iii) Set-up of the instrument - Specially prepared hair ("H") is used as a sensor.
These hairs have undergone special treatment ("S-hygrofix") to make them react
fast. The individual hairs which combine to make the measuring element,
lengthen when the humidity increases and shrink when it decreases. The
change in length is transferred to the rotary axis of a potentiometer. The slider
and the scale indicator are also mounted onto this potentiometer. The external
parts of the instrument are made of stainless steel (V2A).
Since the hygro-transmitters are adjusted uniformly, the plug and the cable can
be exchanged at any time provided that the electrical output is the same.
Hair hygrometer are rarely used for field measurements these days, Modern
Humidity Sensors use a capacitor sensor which has a di-electric that expands or
contracts with change in humidity. This changes the capacitance which is sensed
electronically.
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