Need to capture peak impact

MtnFlyer

I need to measure and capture the peak force (or strain or displacement) of a flat square steel plate, supported·around its edges, and·struck with a rubber mallet. It's for a carnival-type game where people will compete to see how hard they can hit the plate.· The plate is about 12" X 12" X 1/8". Any ideas out there?· The g-loading is likely to be very high (in the 100's) and the pulse duration very short, so conventional accelerometers would be saturated unless they are somehow damped.

Franklin

www.analog.com/en/mems-and-sensors/imems-accelerometers/adxl180/products/product.html

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- Stephen

MtnFlyer

Stephen, thanks very much for the quick response. I'm hoping I don't have to buy 1000 of them to get their $8 price ;^)

MtnFlyer

Stephen, have you seen any applications in which the basic stamp has been used to interrogate this device?

Phil Pilgrim (PhiPi)

I would give one of these piezo elements, or one similar (DigiKey has lots of them), a try. The base is brass, and it can be soldered directly to the underside of the steel plate. When subjected to an impact, it will produce a high voltage peak, which can be divided down and integrated with an op amp, whose output can then be read using an A/D converter.

BTW, are you sure 1/8" is thick enough? I'll bet it gets bent.

-Phil

Craig Eid

MtnFlyer,

The Freescale MMA1200 series of Z-axis high-g accelerometers are commonly used for shock testing and have a maximum range of· ···· +/-169g,+/-225g and +/-250g. The accelerometers·have an analog output with a well controlled gain factor, packaged·in an·SOIC and are ~$12/quantity 1.

MMA1211EG - +/-169g; MMA1212EG- +/-225g; MMA1200EG- +/-250g

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························ Craig Eid


··········· Triad Research and Development
Electical Engineering Design and Consulting Services

··················· www.TriadRD.com

Post Edited (Craig Eid) : 4/8/2009 2:17:27 AM GMT

MtnFlyer

Phil- the plate may be 1/4" thick --- I was working from memory there. Thanks for your suggestion. I'm having trouble finidng a timely source for the imems accelerometer, so the piezo idea sounds attractive.

Craig- thanks for the suggestion. I'm going to take a look at the Freescale devices, too.

--Jim

sylvie369

You may find this thread helpful (if you can ignore the Einstein stuff):

http://forums.parallax.com/showthread.php?p=771713

MtnFlyer

Thanks sylvie369!

Phil- I know what you mean by dividing down the voltage, but can you give me a reference for how to integrate a signal with an op-amp?

Thanks. --Jim

Phil Pilgrim (PhiPi)

Try this: www.wisc-online.com/objects/index_tj.asp?objID=SSE5303.

You will need some way to discharge the cap after taking a reading. This can be done with an analog switch, or simply a large value resistor which bleeds the charge off between impacts.

Another circuit that might be appropriate is an op amp peak detector. Instead of integrating the energy under the voltage curve, this will sample and hold its highest value. Again, a way of discharging the cap, such as a large value resistor, must be included.

-Phil

MtnFlyer

Phil- on the peak detector link diagram there's a "mf" below the 47uf capacitor. What's that referring to? --Jim

Phil Pilgrim (PhiPi)

I have no idea. It looks extraneous.

-Phil