From: uphhsbt@Msu.oscs.montana.edu
Subject: Re: Avocet Low-Speed Inaccuracy
Reply-To: uphhsbt@Msu.oscs.montana.edu
Organization: Montana State University
Date: Tue, 10 Nov 1992 01:33:39 GMT

In article <1992Nov9.161957.1720@ulysses.att.com>, cjc@ulysses.att.com (Chris Calabrese) writes:
>In article <1460013@hplredHPL.HP.COM> jbrandt@hplredHPL.HP.COM (Jobst Brandt) writes:
>>Re: Avocet Low-Speed Inaccuracy
>>
>>Marc Lee writes:
>>
>>> I have an Avocet 40 which gives extremely inaccurate speed readings
>>> (on the low side) at speeds lower than 10mph.
>>
>>This sounds like a faulty instrument to me.  Why not return it and
>>get another one.  Avocet is eager to please the customer so you
>>shouldn't have any trouble with this.
>>
>>jobst_brandt@hplabs.hp.com
>
>I've had an Avocet 30 for about 2 years now, and I'm generally pleased
>with it's speed accuracy.  However, I have noticed some peculiarities
>which I think may be due to software.
>
>When crossing the threshold of 10mph or 20mph (I haven't noticed it at
>30, but then, I don't get up to 30 _that_ often, and I haven't hit
>40 or 50 since the last time I rode in Vermont [I love them downhills...]),
>there seems to be a software bug if you are accelerating quickly
>(maybe that's why I've never seen it at 30, 40 or 50 - I may be
>_moving_, but the acceleration is more gradual).
>
>The symptom is that when you approach the threshold quickly, the
>reading looks something like this (over time):
>	7, 8, 9, 5
>	17, 18, 19, 10
>
>The unit usually corrects itself in around 10-20 seconds.
>
>My best guess is that the system starts intentionally skipping
>interrupts from the sensor at 10mph increments (or maybe it's at some
>metric increment and it happens to occur somewhere near the 10 and 20
>mph marks), and when you are accelerating rapidly, it can't figure out
>which side of the mark you're on (whether to start skipping or not).

This certainly doesn't seem to be the case with mine.  Up until a few months
ago I lived in Boulder and for those familiar with the area I worked at NCAR
and commuted there everyday.  For those not familiar with the area, it is a
labratory located on a mesa about 600ft above town.  This is where I first
noticed the problem.  My fairly constant pace of 10-12 mph suddenly dropped to
3 to 4 mph.  Gee, it sure seemed like I was riding the same.  I then also began
to notice that my round trip mileage was dropping, by almost exactly the amount
of distance I was riding at less than 15mph.  Once I got over about 15 or so it
would work fine and as long as that speed was maintained, it would read
correctly.  The strange thing is that gradual slowing would not affect the
reading until it dropped to maybe 12-13mph.  It also tended to jump around a
lot when it first started doing it.  It eventually settled to reading about 60
percent of my actual speed (and distance).  I have replaced everything
including the battery, except the computer itself .  The computer _should_ be
fine as I never left it out in the weather.  I really have no idea what's going
on with it.

Brett Taylor
>--
>Name:			Christopher J. Calabrese
>Brain loaned to:	AT&T Bell Laboratories, Murray Hill, NJ
>att!ulysses!cjc		cjc@ulysses.att.com
>Obligatory Quote:	``pher - gr. vb. to schlepp.
Newsgroups: rec.bicycles.tech