IAN HANBY - CHARTERED ENGINEER

MICROCONTROLLER INTELLIGENT WINDVANE

For use in wind-directional sampling

CONTENTS OF KIT

  • Windvane

  • Mounting arm

  • Fixing bracket

  • 10-metre cable

  • Microcontroller Enclosure (IP66) 130mm x 130mm x 75mm

  • Instructions




BENEFITS

  • Can be used to convert conventional air samplers into directional instruments

  • Time hysteresis characteristics prevent frequent output switching in turbulent airflows

  • Wide range of input voltages

  • Low current consumption allows battery operation over long periods

  • Microcontroller system allows quick and accurate adjustment of acceptance angle

  • Longer cable available if required (100m max)

  • Fixing bracket allows mounting arm to be fastened to standard television aerial mast components

  • Spares, repairs or modifications always available

  • Microcontroller Electronics can be retro-fitted into some earlier versions of Intelligent Windvane - ask for details

OPERATING PRINCIPLE OF THE WINDVANE

This windvane system is intended for the control of electrically operated devices which are required to operate only when the wind is blowing from a particular sector. When a windvane is observed in normal weather conditions, it will be seen to be oscillating very rapidly about a mean position. If such a vane were directly connected to an air sampler's pump, there would be a great deal of switching on and off which would damage the pump and give inaccurate results due to the finite time which the pump would take starting up and closing down. It is therefore necessary to build some hysteresis into the system. The simple solution is to introduce mechanical damping by friction or viscosity, but devices of this nature are temperature, time and position dependent and completely unreliable. In this instrument it was decided to allow the vane to oscillate freely in very low-friction bearings and to introduce the hysteresis electronically. A digital Schmitt trigger was therefore devised in order that the performance of the vane would be totally predictable.


The windvane itself is an NRG instrument containing a precision potentiometer capable of continuous rotation. The electronic system consists of a PIC Microcontroller with ADCs and EEPROM. When the device is powered up, a count of 127 is placed in a register. If the window detector sees a signal from the windvane within a pre-settable window, the counter is incremented. If the count reaches 256, the microcontroller sets the output high. If the window detector sees a signal outside the window, the counter is decremented. If the count falls to zero, the microcontroller sets the output to 0 volts. If the status of the windvane changes before the count reaches 256 or zero, the count direction changes but the output will not change until the count finally reaches 256 or zero. The microcontroller is programmed such that the counter takes approximately 30 seconds to perform an uninterrupted count from zero to 256. Various LEDs show whether the windvane is above, within or below the sector, and there is an LED which indicates whether the output is on or off. The window, or acceptance angle, is easily set by the user within the range -170° to approximately +170°on either side of the datum position. The window can be set asymmetrically, eg: -100° to +43°, if required.


SPECIFICATION

  • The rotational life of windvane 50 million cycles (typically 2-6 years)

  • Input voltage 5.5v DC minimum, 30v DC maximum (User to supply power source)

  • Input current approx 15mA + output current

  • Output voltage = Input voltage

  • Output current 1 amp max

  • Maximum cable length from windvane to microcontroller enclosure 100m

  • Acceptance angle -170° to +170° (user settable; asymmetrical if required) - angular information stored in EEPROM (40 years' retention with power off or on)

  • Minimum output status duration 30 seconds (manufacturer reprogrammable)

SETTING-UP PROCEDURE - CLICK HERE

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