"Andrew E. Mileski" wrote:
>
> I've seen a few different implementations of varios ...
>
> Use heated wires in a bridge, with half of the bridge inside the flask.
> The resistence of the heating wires change with temperature, and
> unbalance the bridge, causing a measurable output.
>
> Similar to above, but use warmed thermisistors. I think this is what
> the sniffler used, and the flask was only plastic. [Been ages since
> I looked at a sniffler.]
Sorry for the double post, but I remember more now.
The bridge is located outside the flask. One side of the bridge is next
to an air vent that lets outside air flow in/out of the vario. The
other side of the bridge is next to an air vent that lets air flow in/out
of the pressure flask.
Air flowing into the vario and into the flask cools the sensor next
to the outside air vent more. The resistance changes more on the
outside air vent side, unbalancing the bridge. This indicates you
are descending.
Air flowing out of the flask and out of the vario cools the sensor
next to the flask air vent more. The resistance changes more on the
flask air vent side, unbalancing the bridge in the opposite direction.
This indicates you are ascending.
> Use a solid-state differential pressure transducer to measure the
> flow in and out of the flask. Very little power required (no heating).
> This is the simplest to design a vario around.
>
> Use a solid-state absolute pressure transducer to measure the rate
> of change of pressure. Doesn't require a flask, but needs additional
> smarts to output the rate of change.
Measuring absolute pressure gives you slow response. A differential
method is better.
--
Andrew E. Mileski
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