Measuring successive peak heights

[eichlerjw]

OK. Will do that in a minute. I have been adjusting the hardware filtering settings on the load cell amplifier. I was previously using no filtering. Switching in a 100 Hz low pass filter removes most of the noise and leaves only the broad peak that I previously assumed was a secondary impact. It also removes the negative part of the signal. I'm beginning to think that the first narrow peaks are due to vibrations from the impact. I need to raise the low pass filter until I start to see the noise again.

I'll try to get another image from the scope.

cheers

John

[johnsold]

John,

I think you are on the right track.  It is important to know which parts of your signal are due to the excitation and which are responses of your system and which are so modified by your measurement technique as to tell you nothing about the device under test.

Can your load move meaningfully in microseconds?  If not your first fast peaks are just measuring the acoustic wave propagated from the impact.

Lynn

[eichlerjw]

Yep, I agree. I have attached pics of the scope as requested. These are with the filter disabled. The first few oscillations certainly look like vibrations rather than an actual force. I will experiment with LabVIEWs filters to clean up the signal. On the hardware filters 100Hz low pass seems to work OK. 500Hz still has some 'spikes'. There is no 250Hz filter.

Many thanks for your help. Now that the signal has been cleaned up I think the LabVIEW code will be much easier to write.

[eichlerjw]

Screenshot showing the effect of the hardware filter attached.

J

[johnsold]

What is the size and mass of the device being tested?  What is its natural resonant frequency?  What is the mass of the load cell? The piston?  How fast is the piston moving at impact?  Does the piston just stop or does it retract after impact?  How fast are the pneumatic valves?

Sorry for all the nosy questions, but I have seen systems like this which were set up in such a way that the outputs measured anything but what was wanted.

Lynn