I'm capturing load data from impacts with a load cell on the face of a mallet. About half of the time everything works perfectly, but the other half (despite the impacts being similar) it either fails to trigger or triggers part way through the impact trace. I think all the pertinent details are below. Could you please suggest how I could make this reliable.
Thanks
Phil
2205
Picoscope6
Ch A only
500us/div
100kS
Repeat trigger
rising
5% pretrig
Thanks for getting back. The attached file has 2 traces. The second is OK, clearly some zero data at the start. The first has triggered too late on a secondary feature. Obviously there is no record of the ones that didn't trigger at all.
Martyn
I don't have it setup at present, but all the saved files I have are consistant with an impact i.e some zero data while nothing is happening followed by a sharp rise to the initial peak, then some oscillation and secondary features.
Phil
Is it possible that the true trigger point has happened during the re-arm time of the scope that occurs between the blocks and so it picks up on the second peak ? The dead time will be anywhere between 1ms and 60ms, after each block, depending upon PC and USB use.
They are applied by hand, so the time between can't much less than half a second.
When it seemed to be having an issue with not triggering during the test, I did some trial single blows that had 2 or 3 seconds between and the intermittent triggering carried on through these.
I would suggest changing to an Advanced Edge Trigger, add in some hysteresis, move the level to around 3kN and possibly increase the amount of pre trigger.
Martyn,
That seems to have cured it. Triggering has been reliable so far with 400N and 0.5% hysteresis and 10% pre trig.
The threshold can't be raised as some impact peaks are less than 1 kN.
Thanks
Phil