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air tank pressure measurment

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MrDEB

Well-Known Member
got to be a cheaper way than buying a $100 pressure sensor.
want to connect to a PIC to measure air pressure in a air cannon.
this is for an accuracy competition so the air pressure must be some what accurate.
thought about a digital tire gague but connecting and sealing air tight? then connecting to a PIC.
This air cannon, still in design stages will incorporate a muzzle velocity sensor (two photo transistors) with an LCD readout.
a wind speed measurement, would like a digital compass but them sensors are way out there in price.
thinking about a DIY digital compass? to determine adjustment for wind.
by knowing the projectile weight, air pressure and muzzle velocity, one can be pretty accurate in hitting a target consistently.
or at least give it a try..
any ideas??
 

ke5frf

New Member
There are many ways to measure pressure, some more accurate than others, some more simple, some more complex, some more responsive and some with lag or hysterisis.
Piezoelectric sensors and differential pressure are two common ways but more difficult to fabricate.... Or, a mechanical pressure gauge with a bourdon tube or a diaghram/spring can be used to move the wiper on a variable resistor.

If yu wanted to go the DeltaP route, they work on the capacitance between two plates with a flexable diaphragm as the dialectric. One side applied to the diaphragm is the Hi side, exposed to the measured pressure, and the other side is the low side, exposed to a known reference pressure OR atmospheric...that is in the case of measuring positive pressures. Measuring a vacuum, the hi side would be the atmospheric or reference leg and the low side would be the measured vacuum.

In all cases, to fabricate this yourself would require calibration with AT LEAST two reliable pressure sources of known value. Atmospheric would be a reliable baseline and somewhere near your target would be good for the second point. With a homebrew sensor, though, I wouldn't trust the linearity enough for two points.

If it were me, I would rob a pressure transducer from some junked device or order a quality transducer from a reputable company like Omega engineering (Sensors, Thermocouple, PLC, Operator Interface, Data Acquisition, RTD)
 

MrDEB

Well-Known Member
can't think of any junk devices?
thinking about one used on an automobile the remote tire sensors? but only newer cars.
 

Boncuk

New Member
by knowing the projectile weight, air pressure and muzzle velocity, one can be pretty accurate in hitting a target consistently.
or at least give it a try..
any ideas??

Hi MrDEB,

I guess you have item too much in your "list".

Knowing the projectile weight and it's muzzle velocity you are able to calculate the ballistic path of the projectile. The air pressure is just a "nice-to-know" item since speed depends on weight and pressure.

Knowing the pressure is decisive for the strenght of the barrel. Gunmakers use high pressure sensors (in the several hundreds to thousands MPa range) for the design of a gun.

(No Army would like to have the barrel of a 155mm howitzer hit the gun crew) :D

Regards

Boncuk
 
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MrDEB

Well-Known Member
accurate pressure measurment is just part

of the equasion to calculating where the projectile will land.
air pressure is a needed a to know factor in determining where the projectile is to land
 

KMoffett

Well-Known Member
of the equasion to calculating where the projectile will land.
air pressure is a needed a to know factor in determining where the projectile is to land
Are you talking ambient air pressure or tank air pressure?

Ken
 

Boncuk

New Member
I think neither tank air pressure, nor ambient air pressure is required to correct for ballistics.

Tank pressure is irrelevant if weight and muzzle speed are known.

It's air density which is decisive for the shell's resistance to air (as well as the shape of the projectile)

An even more decisive factor is the average wind data along the intended flight path.

For best accuracy the wind direction and speed have to be determined at several points along it.

Artillery gunners use observers to correct for wind effects. :) (no chance to install remote weather stations along a firing range of 15miles)

BTW, do you know that during WWII one of 25,000 shells of all calibers was a hit?

Reducing that to the effectiveness of an air gun you have a good chance to hit "bull's eye" with every 25,000s projectile. :)

Boncuk

P.S. Change your plans to wire guided projectiles.
 
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MrDEB

Well-Known Member
we are measuring tank pressure

planning on doing lots to test fires to determine at what tank pressure the projectile will hit desired target
a wind speed and direction measurement will be included.
need to build an annometer as well.
THEN get the PIC programmed to decipher all this.
a graph will be drawn to take all into consideration.
 

Boncuk

New Member
planning on doing lots to test fires to determine at what tank pressure the projectile will hit desired target
a wind speed and direction measurement will be included.
need to build an annometer as well.
THEN get the PIC programmed to decipher all this.
a graph will be drawn to take all into consideration.

Happy go lucky you. :)
 

MrDEB

Well-Known Member
got to build the chronograph first then an annometer.
I might accidentally learn something!!
like how to spell annometer right??
 

KMoffett

Well-Known Member
I think neither tank air pressure, nor ambient air pressure is required to correct for ballistics.

Tank pressure is irrelevant if weight and muzzle speed are known.

....
Boncuk.../QUOTE]


But, wouldn't tank pressure be the equivalent of powder charge? Isn't muzzle velocity "dependent" on the weight of the projectile and the tank pressure? These you can control before you fire, along with elevation and azimuth. Muzzle velocity is sort of an after-the-fact measurement, like the point of impact, good for future trajectory calculations if the weight and pressure stay the same.

Just musing 'til my morning coffee is brewed. :)

Ken
 
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Boncuk

New Member
got to build the chronograph first then an annometer.
I might accidentally learn something!!
like how to spell annometer right??

I don't know how it's correctly spelled in English. In German it is "anemometer"
 

Boncuk

New Member
But, wouldn't tank pressure be the equivalent of powder charge? Isn't muzzle velocity "dependent" on the weight of the projectile and the tank pressure? These you can control before you fire, along with elevation and azimuth. Muzzle velocity is sort of an after-the-fact measurement, like the point of impact, good for future trajectory calculations if the weight and pressure stay the same.

Just musing 'til my morning coffee is brewed. :)

Ken

Hi Ken,

you are right: The speed of the projectile results from its weight and the pressure it is brought to movement.

If the projectile speed and weight are known it's irrelevant to know the air pressure or gun powder charge respectively. The speed is a result of pressure and projectile weight.

To calculate for a certain firing range you must of course calculate for the necessary pressure and knowing the pressure one must calculate for the necessary strenght of the barrel.

Regards

Boncuk
 
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MrDEB

Well-Known Member
this is an air cannon

or better known as a spud gun
as an example - If we know that with 30psi in the chamber produces a muzzle velocity of say 300fps with a 12oz projectile and the projectile will hit the target at 30 yards
then we get a projectile that weights say 13 oz then the 30 psi won't propel the projectile enough to hit the target at 30 yards.
we draw up a chart using different air pressures with same weight projectile, then determine muzzle velocity = what air pressure = distance.
THEN using a different weight projectile, we can predict what air pressure to use
to obtain the desired distance to hit the target.
several targets are going to be used, 30, 60, and 90 yards.
And yes an anemometer and wind direction measurement will be included.
I posted earlier about using a servo pot to detect wind direction but need info on servo pots connections etc.
am assuming, looking at data sheets that a servo pot is a 360degree rotation pot that would output an analog resistance reading??
 

youtray

New Member
Request Thermocouple circuit

I can not found the circuits that use with thermocouple sensor to measure the temperature although try and try to find in the book and in the internet. Could anyone tell me where can I find the! Thank in advance
 

Boncuk

New Member
I can not found the circuits that use with thermocouple sensor to measure the temperature although try and try to find in the book and in the internet. Could anyone tell me where can I find the! Thank in advance

What has a thermocouple to do with air pressure? Your'e obviously in the wrong thread. Please make your own one.

Boncuk
 
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