[acannell]

Yes, I know the type you are meaning, ones I looked at said operating range something like 0.0007 -7 Bar, so not sure how you would use them as the pressure/force would be a lot more than 7Bar.

Maybe I am just not understanding what it means by that 7 Bar, in fact it is almost certain I am not

Hood

hmm strain gages wouldnt really be rated for pressure i.e. bar, theyd be rated for strain

for instance the design steps for this sort of thing would be like this:

-figure out for forces we are dealing with. for a drawbar force gauge id say 100lbs to lets say 3000lbs would cover pretty much anything. note that its pounds, not psi. force, not pressure.

-select a material and diameter for the rod that will connect the pull stud to the bridge, that will handle the max tension (3000lbs) and also will develop a strain that is not beyond the capability of the strain gage you want to use to measure. typical strain gage limits are on the order of 1000 to 5000 micro strain, i.e. .005 inches per inch increase/decrease of length. so you need to do some physics/material calculations (very basic) to determine how much your bar will lengthen under the max load, and make sure its less than 0.005 inches / inch during 3000lbs (as an example). what that bar diameter and material might be is probably nothing special. id bet just off the top of my head you could use steel, aluminum, whatever, and the range of strain would just shift. i.e. steel would be a smaller range and aluminum would be a larger range because it has lesser youngs modulus and therefore stretches more under a given load.

-now you buy your strain gage off ebay, glue it onto the rod as straight as you can, make a bridge completion circuit, connect the whole thing to a strain gage meter, and voila

-in reality youd probably use some at least a half bridge strain gage to null temperature affects and use a gage with a tempco that matches the material of the rod. but this application is so straightforward it would pretty much work just like i described. i.e. no twisting forces and everything is pretty much in a straight line.