Measuring force

[Forrest Addy]

Gut a cheap digital scale?

[Erich]

It could affect the force by affecting the pressure, whatever. But it doesn't matter as far as determining the force by reading pressure. Force & pressure are simply & always related by the piston area. Period.

minus the force of seal friction. May be negligible, maybe a showstopper, depends on pressure range and type of seals.

On one critical job, we used an airpel air cylinder: glass cylinder, carbon piston, lapped fit no seals.

[garyhlucas]

Pressure gauges were never very accurate and accuracy cost a boat load. Not so much today with strain gauge pressure transmitters. We pay about $125 for 1% transmitters and 1/4% go for maybe $250. They also survive 600% over pressure and can respond in a millesecond or less. So it might be easier than you think.

[Forestgnome]

Air is a compressible fluid, and so there will be Temperature effects as the Pressure/Volume changes occur. When you compress a cylinder of air it heats up. When it expands it cools down. As the Temperature of the air in the cylinder equilibrates with the environment the Pressure will change. Your readings will depend on how fast you read the Pressure gauge after the compression.

The size of this effect will depend on a lot of factors, including rates of measurements, rate of heat transfer from/to the cylinder, relative change in volume / pressure in the cylinders, etc. Seems fraught with possibilities for error.

I was going to mention that. pV=nRT.

[Noitoen]

I've built a conveyour scale with 4 of those pneumatic suspension "balloons" filled with distilled water and 4 little pressure sensors. It works very well.

[Illinoyance]

Banggood.con has some very inexpensive strain gauge load cells..