Chuck wrote:

Here is the instrument I made to replace the water manometer. It is a
Sen-Sym signal conditioned 0 to 1 PSI pressure transducer from DigiKey
$47.70 P/N  287-1002-ND connected thru a voltage divider to a LCD Panel
Meter from Jameco $14.95 P/N 108388 powered by two 9 volt batteries. It is a
differential transducer which means it has two ports.

The transducer has an offset so it reads about 260 at room temp. with the
ports disconnected.  I have to read the offset with no pressure applied and
then subtract that from the reading to get an accurate absolute reading, but
it works great for relative measurements. It will read to .435 PSI or about
11.3" of water or about 150MPH.

Each digit represents .00025 PSI or .0065" of water. Which means it starts
reading at 3.6 MPH if used as an airspeed indicator. Advantages over water
manometer: More resolution, easier to read, easier to mount readout, no need
to add water to replace what evaporates over time. Batteries should last a

2> long time. Disadvantages: Costs more, possibly harder to interpret data.

So far, I have learned that I have hardly any (possibly backwards!)airflow
thru the end of the oilcooler opposite the end where the air comes in. I
will put a new duct on my list of things to do.

Chuck Dunlap

Another disadvantage compared to a water manometer is you can only read
one pressure at a time.

It is also about the same cost as a Dwyer Magnehelec. Maybe a bit more.
No battery required for the Magnelelec.
http://www.dwyer-inst.com/htdocs/pressure/2000.html

Looks like a fun project to build however.

Paul Lamar

I know I'm repeating myself, but I'd recommend the Motorola (MPX...) sensors.
About 1/2 the cost. I get them from Newark Electronics.

Also, since you're using independent power supplies for the panel meter and the
sensor (two batteries), there's no reason why you can't get rid of that offset.
Connect the "common" terminal of the panel meter to a voltage divider.

Finn

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