INTELLIGENT
WINDVANE
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For use in wind-directional sampling
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CONTENTS OF KIT
- Windvane
- Mounting arm
- Fixing bracket
- 10-metre cable
- Allen key, 2.5mm
- Trimmer
- Instructions
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BENEFITS
- Can be used to convert conventional air samplers
into directional instruments
- Time hysteresis characteristics prevent frequent
output switching in turbulent airflows
- Low current consumption allows battery operation
over long periods
- LED output allows quick and accurate adjustment of
acceptance angle
- Longer cable or extension cables available for
certain applications
- Fixing bracket allows mounting arm to be fastened to
standard television aerial mast components
- Spares, repairs or modifications always available
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OPERATING PRINCIPLE OF THE WINDVANE
The windvane consists of a conventional
vane/pointer
system mounted on a 6mm diameter stainless steel shaft running in a
pair of acetal bearings. This shaft drives a precision potentiometer
capable of continuous rotation. The electronic system consists of a
window detector, clock pulse generator and a series of programmable
synchronous binary counters with associated logic gates. When the
device is powered up, a count of 127 is placed in the registers. If the
window detector sees a signal from the windvane within a pre-settable
window, the clock pulses are counted upwards. If the count reaches 256,
the windvane sets the output to +5 volts. If the window detector sees a
signal outside the window, the clock pulses are counted downwards. If
the count falls to zero, the windvane 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 clock pulse generator is set
such that the counter takes approximately 30 seconds to perform an
uninterrupted count from zero to 256. The windvane also sends an output
to drive an optional external low power LED, which indicates the
current status of the vane, i.e. inside or outside the window. The
window, or acceptance angle, is initially set at
�30�, but can be reset
by the user within the range �0� to approximately
�90�.
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SPECIFICATION
- The rotational life of potentiometer 10 million
cycles mechanical
- Input voltage 5v DC (Max 7v)
- Input current approx 5mA + output current
- Output voltage 5v DC
- Output current 20mA max
- LED output to suit HLMP4740 (2mA forward current)
- Acceptance angle �0� to
�90� (user adjustable)
- Minimum output status duration 30 seconds
(manufacturer resettable)
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Operating
Principles and Setting-up Procedure
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This windvane is intended for the control of air sampling 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
the 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 acetal 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 consists basically of a conventional vane/pointer system
mounted on a 6mm diameter stainless steel shaft running in a pair of
acetal bearings. This shaft drives a precision potentiometer capable of
continuous rotation. The electronic system, contained in an IP67 sealed
box, consists of a window detector, clock pulse generator and a series
of programmable synchronous binary counters with associated logic
gates. When the device is powered up, a count of 127 is placed in the
registers. If the window detector sees a signal from the windvane
within a pre-settable window, the clock pulses are counted upwards. If
the count reaches 256, the windvane sets the output to +5 volts. If the
window detector sees a signal outside the window, the clock pulses are
counted downwards. If the count falls to zero, the windvane 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 clock
pulse generator is preset such that the counter takes approximately 30
seconds to perform an uninterrupted count from zero to 256. The
windvane also delivers an output to drive an optional external low
power LED, which indicates the current status of the vane, i.e. inside
or outside the window, irrespective of whether the pump control output
is 0 or +5 volts. The window, or acceptance angle, is initially set at
�30�, but can be reset by the user within the range
�0� to
approximately �90�. There is no in-built heating
system, so the
windvane may ice up in very severe conditions. The electronic
components, however, will function down to about -40�C.
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Set-up Procedure
1. The
balance of the arm and tailfin should be checked by holding
the windvane so that both its main axis and arm/tailfin are horizontal
and then observing whether the arm/tailfin remains horizontal. If a
bias is observed, i.e. if either the nose or tailfin dip, then the
balance should be restored by slackening only the grub-screw at the
very top of the windvane and sliding the arm in the appropriate
direction. A 2.5mm Allen key is provided for this purpose. At the same
time the verticality of the tailfin should be checked and adjusted if
necessary.
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2.
The window, or acceptance angle should now be set. This procedure is
best carried out with the windvane in the relative comfort of ground
level. If the preset arc of �30� is acceptable, or
if the user has
requested some other figure when ordering the instrument, then no
further adjustment will needed. However, should the user need to change
the angle, the following procedure should be adopted:
Set the
arm/tailfin to the required angle and secure using the Allen Key as a
locking pin. If, for example, an arc of �20� is
required, the arm
should be locked to the body of the windvane at either +20� or
-20�
relative to the zero position. A ring of 3mm diameter holes at
10�
intervals is provided for this purpose. Open the IP67 box, power up the
system and adjust the multi-turn potentiometer using the trimmer tool
until the low-power LED (to be provided by the user) is toggling
between on and off (clockwise rotation increases the angle). The arc is
now set to the desired angle. Reseal the lid. |
3.
The windvane can now be fitted to the mast (provided by the user)
using the bracket and clamp provided. Point the body of the instrument
so that the centre of the arc is pointing in the desired direction
(there is a short slot milled into the main body of the windvane
indicating the arc's midpoint) and check using a spirit level that
everything is true. Unlock the arm/tailfin assembly and check that it
can rotate freely with hitting the mast or cables.
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4.
Although the user can alter the timebase speed and hence the
switching, time, this is not advisable unless an oscilloscope is
available. Please note that some of the electronic components are
static-sensitive and can be destroyed by careless touching. |
Pin-out
The cable
from the windvane is terminated in a 6-pin sealed cable plug (Bulgin
Buccaneer) as follows:
- Pin 1 - LED anode - Yellow wire
- Pin 2 - LED cathode - Green wire
- Pin 3 - +5 volt output - White wire
- Pin 4 - +5 volt input - Red wire
- Pin 5 - Timebase output - for test purposes only.
- Pin 6 - 0 volt - Black wire
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