LIQUID LEVEL ,CODE HELP - pressure
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Posts: 46,084
--- In basicstamps@yahoogroups.com, "SB" <steve.brady@r...> wrote:
> How exact do these measurements have to be?
>
> Wouldn't the pressure reading of the tank change with the
atmoshpheric
> change in pressure (I'm thinking when it's full....it obviously
will when
> empty)....
> If you need exact readings then you'd have to set up an external
pressure
> sensor to monitor atmoshpheric changes (IF, it's the amount you're
> measuring)...
>
> If you just want to know when it's empty/half-full/full (ballpark
levels)
> then you won't need it.
Actually, all pressure sensors are what is termed DIFFERENTIAL
pressure sensors.
The oil pressure meter on your 1965 Mustang Convertible has a Bourdon
Tube inside and pressure makes the tube change shape and that in turn
spins a gear that moves the needle.
The inside of the tube is oil pressure, the outside of the tube is
the air, yup. the air you breathe. The difference is shown on the
needle movement. If both sides of the tube are exactly, there is no
difference in pressure and no change can occur.
If you take that same meter underwater it will start to read lower as
the outside pressure will increase, decreasing the differential
pressure.
The pressure sensors you buy have either two tubes so you can select
what reference pressure you want, or the have one tube and the
default is the atmospheric pressure of the device.
And that brings up Boyles Law. With a constant volume, a change in
temperature will result in a change in pressure.
Many liquids are considered non-compressible fluids and do not change
with temperature to any notable degree. But, the AIR in the tank
will. That means that for some short period of time, a temperature
change might result in a change of reading.
An open or vented tank, like a swimming pool or those giant round oil
storage tanks, can use a pressure meter that has one leg at the
bottom and the tube is filled with air. The air will compress and
change pressure on the sensor.
In some more critical applications, they will bubble the tube to make
sure that the oxygen in the tube does not dissolve in the water and
reduce the total volume of gas.
Direct pressure in a tank does not automatically indicate level, but
can be a good representation. Remember, we never really measure the
thing want to measure anyway. The pressure pushes on a diaphragm and
that makes and electrical change, often resistance and we measure the
electrical change and label it pressure.
Like your mercury thermometer, we measure the expansion of gas, or
the expansion of the liquid and calibrate that to some engineering
units.
seems I got a little off the main subject, but I hope this made some
sense.
Dave
http://www.visualmuses.com/chipcircuit/index.html
> How exact do these measurements have to be?
>
> Wouldn't the pressure reading of the tank change with the
atmoshpheric
> change in pressure (I'm thinking when it's full....it obviously
will when
> empty)....
> If you need exact readings then you'd have to set up an external
pressure
> sensor to monitor atmoshpheric changes (IF, it's the amount you're
> measuring)...
>
> If you just want to know when it's empty/half-full/full (ballpark
levels)
> then you won't need it.
Actually, all pressure sensors are what is termed DIFFERENTIAL
pressure sensors.
The oil pressure meter on your 1965 Mustang Convertible has a Bourdon
Tube inside and pressure makes the tube change shape and that in turn
spins a gear that moves the needle.
The inside of the tube is oil pressure, the outside of the tube is
the air, yup. the air you breathe. The difference is shown on the
needle movement. If both sides of the tube are exactly, there is no
difference in pressure and no change can occur.
If you take that same meter underwater it will start to read lower as
the outside pressure will increase, decreasing the differential
pressure.
The pressure sensors you buy have either two tubes so you can select
what reference pressure you want, or the have one tube and the
default is the atmospheric pressure of the device.
And that brings up Boyles Law. With a constant volume, a change in
temperature will result in a change in pressure.
Many liquids are considered non-compressible fluids and do not change
with temperature to any notable degree. But, the AIR in the tank
will. That means that for some short period of time, a temperature
change might result in a change of reading.
An open or vented tank, like a swimming pool or those giant round oil
storage tanks, can use a pressure meter that has one leg at the
bottom and the tube is filled with air. The air will compress and
change pressure on the sensor.
In some more critical applications, they will bubble the tube to make
sure that the oxygen in the tube does not dissolve in the water and
reduce the total volume of gas.
Direct pressure in a tank does not automatically indicate level, but
can be a good representation. Remember, we never really measure the
thing want to measure anyway. The pressure pushes on a diaphragm and
that makes and electrical change, often resistance and we measure the
electrical change and label it pressure.
Like your mercury thermometer, we measure the expansion of gas, or
the expansion of the liquid and calibrate that to some engineering
units.
seems I got a little off the main subject, but I hope this made some
sense.
Dave
http://www.visualmuses.com/chipcircuit/index.html