> The controls consist of two push buttons -     on/off         and
> mode.

> Q1:    How do you change ranges?

> Q2    Bonus question - The instrument will mainly be used to measure
> air speed in ventilation ducts (actually untrue, but that's close
> enough). What units of speed do I intend to leave it set to. Why?

Answers below.
Don't read if you want to try and work it out yourself.

..









































Adjustment:

This was an extremely useful exercise for me (almost worth the cost of 
the device for the lesson alone :-) ) as it showed me that, despite 
the fact that I consider myself (in technical areas at least :-) ) a 
flexible and lateral thinker, the very simple solution never occurred 
to me. I was trapped within certain standard mental boundaries. The 
switch labels helped but the choice was mine.

The conceptual leap that I failed to make is that the on/off switch is 
not one strictly.

When the anemometer is "off", pressing the mode switch will cycle 
through the velocity and temperature unit combinations. The selected 
unit on the LCD 'lights' and steps with each button press.

This arrangement is not at all hard for the designers to do but/and 
leads one to wonder what the device is *really* doing when one thinks 
it is off. Presumably the anemometer sensor powering (if there is any 
powering) is disabled and the thermistor temperature sensor is not 
excited, the main LCD is off, and presumably the processor is off or 
in a very low power mode. Battery current measurements would be 
instructive. Very sneaky.

Range:

Due to use at low velocities I wanted the maximum available 
resolution. Units can be converted or treated as arbitrary for my 
purposes.

        1 m/s ~~= 2 knots ~= 2.25 mph  ~= 3.28 fps = 3.6 kph

So kph gives the highest reading and most resolution for a given air 
speed.

I assume that the unit measures true speed in some internal unit such 
as rotor sensor pulses per unit time, and converts these to 
appropriate readings, so accuracy should not be affected by this 
method. At low air speeds the % difference between steps is liable to 
have a significant effect on the displayed accuracy. At high enough 
air speeds the actual measurement accuracy will predominate.


            Russell


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