I think I know the answer to this but am looking for some confirmation that I am not missing something very obvious. I am looking to make a sort of quick and easy device to measure an applied force. Pretty much a load cell for a press sort of application. I know the usual setup is a suitable oil filled hydraulic cylinder with a gauge attached: squish, read pressure, calculate force using piston area. Simple and straightforward.

Lets say I use the same arrangement except instead of an oil filled system I have a sealed system with just air in it. As the air is compressible the cylinder piston will have lots more spring to it than an oil filled system, but in my case that may not matter. I am looking to measure relatively low forces (5-20 Kg at most) but would like the measurement to be pretty accurate and maybe more importantly, repeatable.

Question is this: Assuming a 1 square inch piston area, if I measure 10 psi, I have 10 pounds on the piston, right? Does the fact that the working fluid is compressible change the overall way this works or skew the results in some way? I am actually embarrassed to ask this as it seems to me really simple physics going on here, but have the nagging sense that I am overlooking something simple and obvious.

Lets say I use the same arrangement except instead of an oil filled system I have a sealed system with just air in it. As the air is compressible the cylinder piston will have lots more spring to it than an oil filled system, but in my case that may not matter. I am looking to measure relatively low forces (5-20 Kg at most) but would like the measurement to be pretty accurate and maybe more importantly, repeatable.

Question is this: Assuming a 1 square inch piston area, if I measure 10 psi, I have 10 pounds on the piston, right? Does the fact that the working fluid is compressible change the overall way this works or skew the results in some way? I am actually embarrassed to ask this as it seems to me really simple physics going on here, but have the nagging sense that I am overlooking something simple and obvious.

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