Avocet 50 and magnetic fields

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Dave Dermott

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Apr 12, 1994, 10:15:40 PM4/12/94
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The sensor for the Avocet 50 ( and 40) is an induction coil that is
very sensitive to alternating magnetic fields . I hold the sensor
within 10 cm of a small transformer or electric motor and speed
measurement goes wild. A 60 HZ source seems to give a speed of 45
km/hr.
The strangest phenomenon was microphonic . I have a small bell on my
handlebar stem. Ringing it sends enough vibration down the front wheel
to the magnet to give a reading of about 2 km/hr.
So has anyone noticed any strange speed readings when riding by power
lines, big transformers etc ? Maybe the induction coils for traffic
signals also effect it but I think the frequency is around 100 KHZ which
is probably outside the frequecy response of the Avocet's electronics.

David Dermott
Dartmouth NS Canada

Mike E. Locke

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Apr 13, 1994, 12:35:32 PM4/13/94
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Not one smidgen of trouble on my Avocet 50. My cateye micro gives false
readings all the time, as does my wireless Acurex HRM.

btw: the cadence pickup uses a magnetic relay.


---
--
S'later, Mike Locke


Scott Silvey

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Apr 13, 1994, 7:56:01 AM4/13/94
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% So has anyone noticed any strange speed readings when riding by power

% lines, big transformers etc ? Maybe the induction coils for traffic
% signals also effect it but I think the frequency is around 100 KHZ which
% is probably outside the frequecy response of the Avocet's electronics.

Riding home from work yesterday, I got an average speed of like 12mph and
a max speed of 66.5mph. Luckily I didn't pass any cops on the way...

Scott

PS: Anyone else ever had any spurious errors like this before?

Jobst Brandt

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Apr 13, 1994, 6:39:49 PM4/13/94
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Scott Silvey writes:

> Riding home from work yesterday, I got an average speed of like 12mph and
> a max speed of 66.5mph. Luckily I didn't pass any cops on the way...

Sounds like you have a loose contact somewhere like at the pickup where the
wires go into the coil (these were formerly plug-in points) or your handle
bar mount cable is separating where it enters the mount. Loose contacts can
subdivide signals randomly and cause undefined output.

jbr...@hplabs.hp.com

Alan Bloom

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Apr 13, 1994, 7:39:08 PM4/13/94
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Dave Dermott (der...@pig.drea.dnd.ca) wrote:

: The sensor for the Avocet 50 ( and 40) is an induction coil that is
: very sensitive to alternating magnetic fields . ...
: So has anyone noticed any strange speed readings when riding by power


: lines, big transformers etc ?

No, but one of my 2 Avocet 50's has developed an intermittent cumulative
altitude reading. (At least I don't THINK I rode 11,000 feet on last
weekend's ride when everybody else only managed 5000 ft!) The altitude
reads fine, it's only the cumulative total that intermittently goes
berzerko.

Anybody else have a similar problem?

Alan Bloom

Akkana Peck

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Apr 13, 1994, 9:39:45 PM4/13/94
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Scott Silvey <sc...@con.Berkeley.EDU> wrote:
>Riding home from work yesterday, I got an average speed of like 12mph and
>a max speed of 66.5mph. Luckily I didn't pass any cops on the way...
>PS: Anyone else ever had any spurious errors like this before?

All the time. I never use my max-speed reading, because it's always
showing numbers like 50-70mph (not likely, or Cannondale would have been
recruiting me instead of Missy for their downhill team!)

It's just another annoyance I put up with to get the altimeter, like all
the other Avocet annoyances: the useless 2-hour stopwatch, the batteries
that only last six months, the sensors that don't fit without
modification any wheel or fork known to man (well, not on any bike
I've ever owned, anyway).

I wish someone besides Avocet would make an altimeter computer!

...Akkana

Benjamin Liu

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Apr 13, 1994, 10:29:32 PM4/13/94
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jbr...@hpl.hp.com (Jobst Brandt) wrote:
> Scott Silvey writes:
>
> > Riding home from work yesterday, I got an average speed of like 12mph and
> > a max speed of 66.5mph. Luckily I didn't pass any cops on the way...
>
My friend and I decided to test this vibration/magnetic stuff theories.
We took an electric razor and put it up against the sensor (while standing
still) The Avocet 40 maxed out at 98.5mph while a 30 maxed at 66.5.
Not bad:) Guess I'll just have to avoid those electric razors on the road!
Ben

--
Benjamin Liu
bl...@hmc.edu
Claremont Colleges Cycling Team - Race Director
Chevrolet LA Sheriff/Am.Heart Assoc. HeartRide '94 - Logistics Coordinator
--

==========================================================================
Benjamin Liu bl...@hmc.edu Cars Suck... RIDE A BIKE!
340 E. Foothill Blvd. (909) 398-4784 =====--- ___o

Andy Nourse

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Apr 14, 1994, 12:48:30 AM4/14/94
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In article <SCOTT.94A...@con.Berkeley.EDU> sc...@con.Berkeley.EDU (Scott Silvey) writes:
>% So has anyone noticed any strange speed readings...

Mostly that it seems to read 0.00 all the time going uphill,
and doesn't count any of that in the distance total.

I'm slow, but not *that* slow.
I've moved the sensor as close to the magnetic ring as possible, no change.

Paul B. Anders

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Apr 14, 1994, 11:35:31 AM4/14/94
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My experience with the Avo 50 speedometers has been different. I've used
one for the past three years, with none of the problems described above
regarding max speed. In fact, my complaint is that the recorded max speed
is usually 0.5 mph less than indicated max speed (a nit maybe, but not when
you are doing sprint training). As for the batteries lasting 6 months, I've
found they last about a year. Jobst mentioned something recently about a
firmware bug that results in rapid drain, and a fix. Perhaps he could
repost. As for the sensors not fitting to any wheel or fork, I've currently
got mine mounted on the following bikes: Bridgestone RADAC road bike,
Specialized Epic, Specialized M2 and Stumpjumper (Future Shock) MTB's, and
my track bike. The only mod I had to do was to use tie-wraps to hold the
sensor on my high-flange track hub.

The only time I've had to return an Avo 50 to the factory was when I wore
out the contact pins on the back by repeatedly mounting/dismounting the
unit. The unit has been remarkably accurate in all functions, and is very
simple to operate.


--
****************************************
* Brad Anders * Sunnyvale, CA *
* ban...@netcom.com * *
****************************************

Tom Lawrence

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Apr 14, 1994, 6:10:52 AM4/14/94
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In article <Co81p...@srgenprp.sr.hp.com> al...@sr.hp.com (Alan Bloom) writes:

No, but one of my 2 Avocet 50's has developed an intermittent cumulative
altitude reading. (At least I don't THINK I rode 11,000 feet on last
weekend's ride when everybody else only managed 5000 ft!) The altitude
reads fine, it's only the cumulative total that intermittently goes
berzerko.

Anybody else have a similar problem?

I'm now on my 3rd Avocet 50. The first had a short circuit that
drained the batteries in a day or so. The second registered wildly
fluctuating altitude after about a year of trouble free use. I just
took it in and got it replaced a few days ago. When I left my house
the altimeter read 6000 ft. When I got to the store, it read -300 ft.
The ride was flat, incidentally.

The only good thing I can say about the 50 is the replacement policy.
I've replaced it twice with no hassle and no receipt.

--
Tom Lawrence
t...@sgi.com

Jim Siler

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Apr 14, 1994, 1:34:51 PM4/14/94
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Paul B. Anders (ban...@netcom.com) wrote:
[much stuff deleted]
: As for the batteries lasting 6 months, I've

: found they last about a year. Jobst mentioned something recently about a
: firmware bug that results in rapid drain, and a fix. Perhaps he could
: repost.

: --

: ****************************************
: * Brad Anders * Sunnyvale, CA *
: * ban...@netcom.com * *
: ****************************************

I'm not JB but the trick is now packed with the batteries that
Avocet distributes. As I remembr it, after putting the batteries
in remove one until the display goes out and then immediately replace
it. The batteries should then last for a year or more (Avocet tech
support estimate, mine is only 3 mos. old).

jim
--
Jim Siler (a.k.a. k...@panix.com a.k.a. j...@ksi.com)
Kovitz Systems, Inc. "You can believe me, because I
80 Wall Street never lie and I'm always right"
New York, NY 10005 212.425.4840 George Leroi Tirebiter

Cecil Williams

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Apr 14, 1994, 4:14:39 PM4/14/94
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I went to a "warehouse clearance sale" put on by several local
bike shops Wednesday, just to "look around", and ended up buying
a '93 Trek 7900 carbon-fiber and aluminum hybrid.

I've been riding a heavy and sloppy REI Corsa Hybrid for several years
for commuting and general riding, and I like the hybrid ride enough
that I almost never get my old Trek/Campy road bike out anymore. What
the hybrid sacrifices in absolute speed, it makes up for in riding
comfort (except for lack of hand positions) and just plain fun.

I've owned this new Trek 7900 for 25 hours now, and have not yet had a
chance to ride it! (Except for the parking lot test ride, which doesn't
count). I am itching to get out on the road with it, but unfortunately
prior commitments have me hog-tied until Saturday afternoon. @$@$@!#!

I'd like to hear the good, the bad, and the ugly from anyone out there
who has experience with the Trek carbon-fiber bikes. Do I have to baby
this frame to keep from breaking it?(ie don't bang it on rocks or logs,
don't let the handlebars whip around into the frame, be extra careful
to prevent scratches, that sort of thing)

I've never had anything but steel frames before. Is this carbon frame
stiff enough to load up with racks and panniers for touring and not
have to worry about front wheel shimmy or frame-whip (or whatever it's
called)?

The list price was $999.
This was the only one they had, and it was marked down to $799.
Is that a good price?

I need to go buy a new cycle-computer for it now. What's the "best"
new cycle computer? I don't need altitude or heart-rate, and I want one
that the battery will last years and not months...


Email or post;
Any comments welcome...


Cecil Williams
cec...@access.isc-br.com


Jeff Orum

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Apr 14, 1994, 5:42:33 PM4/14/94
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Andy Nourse (xep...@netcom.com) wrote:

> Mostly that it seems to read 0.00 all the time going uphill,
> and doesn't count any of that in the distance total.

I have a similar problem. When I get to speeds under 6 MPH, I find the Avocet
50 often reads about in the 2 to 3 MPH range and will then jump up to over
6 MPH. Sometimes it is as low as 0.5-1MPH and I know I am going faster
than that because the people I am riding with at the same pace have
cyclometers showing them going 5 to 6 MPH.

I have adjusted the pickup several times (and so have dealers) and it is now
almost touching the magnetic ring.

It appears that the unit is much more sensitive to the pick up location at
slow speeds than at fast speeds.

At least it doesn't read 0 MPH so I do get credit for my uphill motion.

It also motivates me to keep my speed above 6 MPH!

Jeff Orum
or...@cup.hp.com

Bill Broadley

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Apr 14, 1994, 5:39:20 PM4/14/94
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I noticed on at least 2 different bike computer's that 0 Mph is displayed
anywhere below 3.5 Mph.

Which BTW is a reasonable speed when biking uphill at 10,000 feet after
a 4,000 foot climb, even when on pavement.

I didn't bother to check the distance. Just thought I'd mention that
even properly setup computers often read zero.

--
Bill Broadley@{neurocog,schneider3,lrdc5}.lrdc.pitt.edu (in order of preference)
Linux is great. Bike to live, live to bike. PGP-ok

Alan Bloom

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Apr 14, 1994, 2:49:08 PM4/14/94
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Akkana Peck (akk...@moab.wpd.sgi.com) wrote:

: the other Avocet annoyances: the useless 2-hour stopwatch,

Huh! That's the feature I use the most. (I like to keep a log of my
commuting time to see how I improve.)

: the batteries that only last six months, the sensors that don't fit without


: modification any wheel or fork known to man (well, not on any bike
: I've ever owned, anyway).

Get a road bike!

Alan Bloom (hunkering down to avoid the flames :=)

Alan Bloom

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Apr 14, 1994, 2:54:21 PM4/14/94
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Andy Nourse (xep...@netcom.com) wrote:

Make sure the magnet is mounted with the correct side out. There's a
big difference in sensitivity. Ditto the pickup. (The bike shop actually
mounted mine with the wrong side of the pickup pointing in! It "kind of"
worked...)

Alan Bloom

Jobst Brandt

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Apr 14, 1994, 2:24:58 PM4/14/94
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Andy Nourse writes:

> Mostly that it seems to read 0.00 all the time going uphill,
> and doesn't count any of that in the distance total.

> I'm slow, but not *that* slow.
> I've moved the sensor as close to the magnetic ring as possible, no change.

Maybe you are not aware of the intended use of this instrument. If you took
it to your dealer, it could be made to register, speed, distance, time, and
altitude and you wouldn't have an electronic zero to look at all the time.
I think the manufacturer intended it to do more than that.

jbr...@hplabs.hp.com

I.F. Brown

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Apr 14, 1994, 8:00:10 PM4/14/94
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In article <2oi6t1$i...@fido.asd.sgi.com>,

Akkana Peck <akk...@moab.wpd.sgi.com> wrote:
>
>I wish someone besides Avocet would make an altimeter computer!
>
> ...Akkana


You can always buy the watch, Casio do a very nice one for 70 quid
(i.e. 70 dollars!)

Ian.

George Carter

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Apr 15, 1994, 12:27:45 AM4/15/94
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>In article <2oi6t1$i...@fido.asd.sgi.com> akk...@moab.wpd.sgi.com (Akkana Peck) writes:
>>All the time. I never use my max-speed reading, because it's always
>>showing numbers like 50-70mph (not likely, or Cannondale would have been
>>recruiting me instead of Missy for their downhill team!)
>>
>>It's just another annoyance I put up with to get the altimeter, like all
>>the other Avocet annoyances: the useless 2-hour stopwatch, the batteries
>>that only last six months, the sensors that don't fit without
>>modification any wheel or fork known to man (well, not on any bike
>>I've ever owned, anyway).
>>
>>I wish someone besides Avocet would make an altimeter computer!

In <bandersC...@netcom.com> ban...@netcom.com (Paul B. Anders) writes:

>My experience with the Avo 50 speedometers has been different. I've used
>one for the past three years, with none of the problems described above
>regarding max speed. In fact, my complaint is that the recorded max speed
>is usually 0.5 mph less than indicated max speed (a nit maybe, but not when
>you are doing sprint training).

Yes, this small quirk is more annoying than one might suspect. Is this
because the processor is not fast enough to both keep up with the input
coil and save the max speed to memory or is the processor capacity
there but the programmer screwed-up in not saving max speed more
often? I suspect the later. How long could it take to do a compare
and store?

I should say that my experience thus far is that the Avocet 50 is the
most reliable bike computer I've ever used. I bought one when they
first came out and it still works. The old cateyes lasted about a
year for me and were thus a big disappointment. The only erratic
readings I've seen were when I parked right next to a large neon
light (15kv transformer).

Torsten Lif, Cyberspace Cyclist

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Apr 15, 1994, 7:56:36 AM4/15/94
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In article C...@cup.hp.com, or...@cup.hp.com (Jeff Orum) writes:
>Andy Nourse (xep...@netcom.com) wrote:
>
>> Mostly that it seems to read 0.00 all the time going uphill,
>> and doesn't count any of that in the distance total.
>
>I have a similar problem. When I get to speeds under 6 MPH, I find the Avocet
>50 often reads about in the 2 to 3 MPH range and will then jump up to over
>6 MPH. Sometimes it is as low as 0.5-1MPH and I know I am going faster
>than that because the people I am riding with at the same pace have
>cyclometers showing them going 5 to 6 MPH.
>
>I have adjusted the pickup several times (and so have dealers) and it is now
>almost touching the magnetic ring.

I have to chime in with the others who have pointed out that there is a
"front" and a "back" side to both the magnet ring and the pickup coil.
Are they *really* facing the right way? Mine picks up signals
flawlessly with a 6mm (1/4") gap.

>It appears that the unit is much more sensitive to the pick up location at
>slow speeds than at fast speeds.

Of course it is. Induced current in a coil is proportional to dB/dt
(change of magnetic field over time) so the faster the change, the
stronger the signal. Sheesh.

---
Torsten Lif
Ericsson Telecom AB, EO/ETX/TX/AD
S-126 25 STOCKHOLM, SWEDEN
Phone: +46 8 719 4881

Paul B. Anders

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Apr 15, 1994, 11:32:29 AM4/15/94
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In article <Co9qy...@cup.hp.com> or...@cup.hp.com (Jeff Orum) writes:
>Andy Nourse (xep...@netcom.com) wrote:
>
>> Mostly that it seems to read 0.00 all the time going uphill,
>> and doesn't count any of that in the distance total.
>
>I have a similar problem. When I get to speeds under 6 MPH, I find the Avocet
>50 often reads about in the 2 to 3 MPH range and will then jump up to over
>6 MPH. Sometimes it is as low as 0.5-1MPH and I know I am going faster
>than that because the people I am riding with at the same pace have
>cyclometers showing them going 5 to 6 MPH.
>
>I have adjusted the pickup several times (and so have dealers) and it is now
>almost touching the magnetic ring.

I have used an Avocet 50 for a couple of years without the problem you
describe. I have the pickup very close (nearly touching) the magnetic
ring, and the unit registers speed down to 0.5 mph (verified this morning
by slowly spinning the wheel). The only suggestion that I can think of is
that it may be possible that the wrong side of the pickup positioned next
to the magnet.

George Carter

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Apr 16, 1994, 11:44:25 AM4/16/94
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In <bandersC...@netcom.com> ban...@netcom.com (Paul B. Anders) writes:
>In article <Co9qy...@cup.hp.com> or...@cup.hp.com (Jeff Orum) writes:
>>Andy Nourse (xep...@netcom.com) wrote:
>>
>>> Mostly that it seems to read 0.00 all the time going uphill,
>>> and doesn't count any of that in the distance total.
>>
>>I have a similar problem. When I get to speeds under 6 MPH, I find the Avocet
>>50 often reads about in the 2 to 3 MPH range and will then jump up to over
>>6 MPH. Sometimes it is as low as 0.5-1MPH and I know I am going faster
>>than that because the people I am riding with at the same pace have
>>cyclometers showing them going 5 to 6 MPH.
>>
>>I have adjusted the pickup several times (and so have dealers) and it is now
>>almost touching the magnetic ring.

>I have used an Avocet 50 for a couple of years without the problem you
>describe. I have the pickup very close (nearly touching) the magnetic
>ring, and the unit registers speed down to 0.5 mph (verified this morning
>by slowly spinning the wheel). The only suggestion that I can think of is
>that it may be possible that the wrong side of the pickup positioned next
>to the magnet.

A properly positioned pickup should have the wires on the inside,
close to the wheel. Some people mount it backwards to "protect"
the wires.

Another suggestion is to try replacing the magnetic ring. A previous
Avocet I had quit working, believe it or not, because the magnetic
ring died. I am not making this up. I assume normal wheel shock
causes this. Avocet is great about selling all the parts
individually.

Also, clean the contacts on the mount and computer.

Jim Siler

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Apr 17, 1994, 11:28:48 PM4/17/94
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Does anyone know if the smoothing algorithm used in the 50
might have something to do with these funny readings? It
seems to me that at very low speeds (e.g., when walking the
bike) the readings tend to be erratic and often low, while
the average speed and distance readings seem quite reasonable.

Can't be sure though, since I usually prefer to ride rather
than walk.

Mike E. Locke

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Apr 18, 1994, 1:33:27 PM4/18/94
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Some things I am trying to remember accurately:

The Avocet 50 has a minimum speed, below which it does not register your
mileage. This is part of the autostop feature. This feature is programmable
when you set up the cyclometer. Could people who have the readings suddenly
drop to zero at low speed have this setup wrong?

The Avocet 50 seems to count pulses from the ring to accumulate distance and
average speed. Recalibrate your wheel diameter or change the units and the
accumulated readings change accordingly. While current speed is displayed
in increments of 0.5 mph, it appears to be calculated more accurately. To
observe this, watch the speed arrow while your speed changes slightly, near
the current average speed reading. The arrow will change direction even when
the speed reading does not change. This calculation, combined with slightly
different rounding algorithms may account for the max speed problems others have
reported. It is possible that the max speed number is more accurate than the
average speed number (I don't know this for sure, maybe Jobst could offer some
info).

Jobst Brandt

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Apr 22, 1994, 12:39:55 PM4/22/94
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Mike E. Locke writes:

> The Avocet 50 has a minimum speed, below which it does not register
> your mileage. This is part of the autostop feature. This feature is
> programmable when you set up the cyclometer. Could people who have
> the readings suddenly drop to zero at low speed have this setup wrong?

The instrument ceases to collect information when the sinusoidal
signal from the pickup (20 poles/rev) falls below a threshold that is
not programmable. The signal level is dependent on speed, pickup to
sensor spacing and the level of magnetism in the ring. The
transmitter ring can be assembled with the magnet backwards if taken
apart or without the soft iron return ring , or be demagnetized by
coming close to a stronger magnet.

> The Avocet 50 seems to count pulses from the ring to accumulate
> distance and average speed. Recalibrate your wheel diameter or change
> the units and the accumulated readings change accordingly. While
> current speed is displayed in increments of 0.5 mph, it appears to be
> calculated more accurately. To observe this, watch the speed arrow
> while your speed changes slightly, near the current average speed
> reading. The arrow will change direction even when the speed reading
> does not change. This calculation, combined with slightly different
> rounding algorithms may account for the max speed problems others have
> reported. It is possible that the max speed number is more accurate
> than the average speed number (I don't know this for sure, maybe Jobst
> could offer some info).

The arrow you mention tells whether your current speed is above or below
the computed average to about 1/100 of the units displayed. All speeds
are smoothed and this, although more convenient to read, clips short term
speed excursions such as maximum speed through a steep dip. I prefer to
see a fluctuation in speed rather than miss the top speed. The classic
is the first dip after the summit of Sonora pass where substantial speed
is achieved for about a second just before severe braking up a 15% grade.
Having an AVO30 and AVO50 side by side on the same pickup, I have
registered unflattering differences here.

The AVO50 stores arbitrary unaltered units that are based entirely on
the number of counts that come in from the pickup. These counts are
converted to speeds and distances on the basis of the calibration
number. Changing from English to metric obviously can be done with no
data modification and accurately by this method. Now this may seem
logical and self evident on first inspection and so it happened. Only
later was there a suggestion that the user may want to use this on more
than one bicycle and that these might have different wheels. For many
users, this is not a problem.

This computational problem was resolved in the new AVO35 and AVO45
that can change both units and calibration numbers without altering
data integrity. Because the AVO30 does no computation, it collects
data based on the calibration number. Therefore, the calibration can
be changed but the units cannot, because the collected data is
absolute and contains units such that changing units would collect
mixed data.

jbr...@hplabs.hp.com

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