response 1 of 43:

May 28 14:02 UTC 1993

One pin gets +5v, the other com and the third is hi or low, depending
on the sense and presance of a magnet, for a digital device.
The device No's you list are not in my Sprague catalog.  Prob. too
old.  Give Reptron a call at 1-800-521-4978.  They handle Sprague and
should be able to send you the info.  (Sprague: (603) 224-1961)

response 3 of 43:

Jun 1 18:12 UTC 1993

I would guess that the device is digital and has an open collector
output.  In order to drive TTL logic with it, you need not only tie
the output of the hall device to your logic but also to a 1.2K or so
resistor connected to +5V.  This is commonly refered to as a "pull-up
resistor".  If you use CMOS logic, you can increase the resistors 
value by an order of magnitude, thereby reducing power consumption.
(10 or 12K, maybe more?)
(I have thought or doing a similar thing for my wife's rowwing shell.
Just connect your propeller/magnet setup to a bicycle odometer/speed-
ometer/etc.  They are cheap, about $20 - $30, and may well be compatable
with a hall device (most use a simple magnetic reed switch, wouldn't
have to add the pull-up ;-) and are fully programable so far as the
the No. of rev's per mile/kilometer/nautical mile/ etc.)

response 5 of 43:

Jun 3 12:20 UTC 1993

If you give the propeller a lot of pitch, I would think it's rotation
rate vs speed would become fairly linear.

TTL for dummies?  How about Lancaster's book "TTL Cook Book" or "CMOS
Cook Book"?  Jung also does a good job with instructional books.  See
your local Purchase radio, Wedon'thaveitmeyers or Borders.  Radio Shack
has also surprised me with the quality content of there books over the
years.

response 7 of 43:

Jun 3 18:03 UTC 1993

Calibration? Try this model:
  
Make about 3 tests wherein you pour/pump/squeeze/whatever a known quantity
of liquid through the measuring-unit and time it. Also (if possible) use
the thingie to count the number of rotations.
  
In each of the tests, chanzge the amount of liquid by a large amount and at the
susing integer multiples of the original amount. See if there is a good fit
or not between the linerity of the time, counts, etc. Then, the easist thing
to do would be to make a paper chart with the "prop count number" and the 
"volume of stuff having passed."
 
Then, just for kicks-n-grins, flow a lot of stuff through it and capture the
liquid output, read the prop-counts, and see if the results make sense.
  
Oh, measure the captured output, natch ...
 
How crude/fine of a measure do you need? There will *always* be a mis-measure
of some magnitude. If it's within whatever tolerance you can live with, quit
playing and get back to work!  <g>

response 9 of 43:

Jun 4 08:41 UTC 1993

It also sounds as if you'll be wanting to measure "an *awful lot* of
liquid." Also, if there is going to be "slipppage" in the measurement,
("the unit will be used in open flow") then you're measurements will
NOT have a lot of relevance to that flow! For it to work with any
degree of accuracy, +all+ the liquid has to be directed through the
propeller blades, with as little as posible "slipping by," un-measured.

response 11 of 43:

Jun 4 15:20 UTC 1993

That 2.0 is the pitch ratio. The prop is 2 inches, so the pitch is 4
inches. I want the device to measure the flow rate of small streams.
I can measure the depth/width cross section, and a few velocity points.
Well, I do have good connections at UM (I work there), but hesitate
to use all that high tech for my low tech gadget - they would say,
why don't you just buy one, instead of spending all this time making
one? (And they would have a point: a mechanical one costs $230, though
props with electronic counters start at $1300.) I do like your calibration
system, Klaus - of course, need some long wires to start and stop the
counter - maybe add radio control? For calibrating with a boat - I
thought that the boat could glide between two marks, at different initial
velocities. A measurement of the distance and the time would give the
average velocity, and of course the revolutions and time give the average
velocity too. Well, I haven't given this up, yet. I have both a canoe
and a sailboat myself: this will be a stimulation to get them in the
water more often. 

response 13 of 43:

Jun 5 05:55 UTC 1993

A shroud (tube) isn't used in the commercial systems. The mechanical
ones use *very* high pitch props (to overcome friction), while the
electronic ones have more normal pitches (I have a catalog in which I
can look at the designs). The paddle-wheel type is used in pipe flow
applications; of course, for making submerged measurements (the "standard"
is to measure at 60% of the total depth, as there is a vertical velocity
profile in a stream), a prop is needed. The commerical devices claim
1% accuracy, but of course they have been calibrated. I cannot tell
whether the electronic units use *nonlinear* calibrations. 

The purpose of the device is to monitor the resurgence flow from a
spring in an area known as the Fiborn Karst Preserve, owned and managed
by the Michigan Karst Conservancy, a non-profit corporation. I am the
chair of the science subcommittee of the preserve. Lots of different
science is being done there; I am working on hydrology and geochemistry.
Its part of a serious avocation, but also legitimate research. Well,
I'm still gathering parts. 

response 15 of 43:

Jun 7 05:27 UTC 1993

There are probably numerous suppliers. My catalog is from Forestry
Suppliers, Inc (Jackson, MS) who, incidentally, is a great source for
all types of professional outdoors technology (but not for lightweight
hiking and camping, etc). It is a lot of fun, though I expect the trip
this June will be overrun by black flies! 

response 17 of 43:

Jun 7 13:38 UTC 1993

That is a most sensible suggestion. I may know someone that has access
to one.

response 19 of 43:

Jun 8 11:30 UTC 1993

You could also measure the rate at which a length of string is unreeled
from the boat to a fixed point on the shore.  Since your prop has a 4"
pitch, you could make a pinch roller with a 4" circumfrance, also set up
with a hall device.  If the prop behaves as an ideal one, there should
be a one to one corelation to the "tick" marks from both devices.

If you can't borrow one, have a sales rep. loan you one to "try out"
for a while ;-)

response 21 of 43:

Jun 11 06:39 UTC 1993

In sailing circles speed boats are called "stinkpots". Also, that's faster
than most streams flow (unless you go over the waterfall). 

response 23 of 43:

Feb 16 13:56 UTC 1997

Hmmm...

The project I did with HE sensors was for controlling motors on a Leslie
rotary organ speaker.  I used unipolar sensors, since the bipolar sensors
require a *reversed* magnetic field to switch back to "off".  I used the Radio
Shack magnets since they were very light and therefore would not affect the
spin balance of the rotors.  I also tested optical sensors (decided that stage
lights might be a problem) and reed switches (too noisy for a recording
studio).  

The Hall Effect sensors have a 5V logic output which does not need to be
debounced.