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

Heater : 75 W regulated by means of a
thermostat
Switch-on and switch-off : 5.5 o C + 3 o C on, 11 o C + 2.5 o C off
temperature
Operating voltage
Electronic : + 15 V/60 mA
Heater : 24 V/3 A
Connection : 19 pol. Euchner plug
Case material : GD-A1, sea waterproof
Transmission line
lon
: LiCY 16x0.75, max. 0 20 mm, 100 m
Recomm. mast dimensions : Threaded pipe 1 1/2" in accordance with
DIN 2441
Dimensions : See scale drawing (Figure-3).
Wind stress at 35 m/s : Approx. 5 kp
Weight : 3.2 kg
(iv) Set-up and Mode of Operation - Wind direction is detected by means of a
highly sensitive light metal wind vane whose ball-bearing pivot is connected to a
code drum. The casing of the code drum has a code pattern which can be
scanned opto-electronically. The resolution of the code pattern amounts of 144
steps per 360 o . An 8-bit binary information has been used i.e. the code drum has
8 scanning tracks. The Gray Code which counts up from 0...71 and down from
71...0 has been utilized. Seven tracks are required for this while the 8th track
serves to differentiate between up and down. The scanning of the code pattern
is carried out by means of optical reflective sensors where a diode emits an
infrared ray which is reflected by the drum casing surface onto a photo-transistor.
The output voltage of the transistor depends on the position of the drum (the
degree of reflection). The degree of reflection of the drum background is less
than of the code pattern bus is still nonzero. A drop-page of the signal voltage
below the lower trigger level indicates a malfunction of the corresponding
scanner component and a warning signal is given. Alternatively a potentiometer
direction sensor can be used where the wind vane is coupled to a 5 K
potentiometer.
Opto-electronic semiconductor components are influenced by temperature
fluctuations and by ageing. Thus, the diode current in the sensor must be
adjusted so as to compensate for interference. For this purpose, an additional
continuous tract is scanned and the output voltage is kept constant with the
regulated diode current. If, transmission factor changes due to the influences of
temperature or ageing, this will be automatically taken into account and the diode
current will be readjusted. Wind velocity is recorded by means of a highly
sensitive rotating cup anemometer whose ball bearing pivot is connected to a
slotted drum. The slotted drum is also scanned opto-electronically.
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