Oznog
Active Member
I want to create a device to measure the peak force of a high speed impact (100 fps) to evaluate the effectiveness of various padding solutions. The target should not move, since this would absorb impact energy and invalidate the result. So ratcheting springs, penduluming targets, etc are not a valid solution. My calcs show that in order to get acceptable approximations, the response would need to be on the order of 100uS, like 10KHz or so.
My first thought was to start with the sensor from a bathroom scale. I do not expect peak forces to exceed 200 lbs so it should have been fine. However, what I discovered was not encouraging. Instead of the Wheatstone bridge load cell I was looking for, there was a long, thin inductor coil with a moveable core somehow pulled back and forth with the weight. This certainly can't be adapted for impact sensing since this would be some sort of oscillator with a relatively high settling time, and the counter required to digitize it is also difficult to construct as a high speed solution.
Now keep in mind that scale was an old piece of crap, it's 10-20 years old. Does anybody know if they still use these variable inductor things or if they went to load cells in current models?
Or can someone think of a better solution? I looked on eBay for load cells, and they were all pretty pricey and all one-of-a-kind odd buys. With the bathroom scale I can get a replacement if I break one or someone thinks it's a good idea and wants me to build another one.
My first thought was to start with the sensor from a bathroom scale. I do not expect peak forces to exceed 200 lbs so it should have been fine. However, what I discovered was not encouraging. Instead of the Wheatstone bridge load cell I was looking for, there was a long, thin inductor coil with a moveable core somehow pulled back and forth with the weight. This certainly can't be adapted for impact sensing since this would be some sort of oscillator with a relatively high settling time, and the counter required to digitize it is also difficult to construct as a high speed solution.
Now keep in mind that scale was an old piece of crap, it's 10-20 years old. Does anybody know if they still use these variable inductor things or if they went to load cells in current models?
Or can someone think of a better solution? I looked on eBay for load cells, and they were all pretty pricey and all one-of-a-kind odd buys. With the bathroom scale I can get a replacement if I break one or someone thinks it's a good idea and wants me to build another one.
