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mma8453q - inconsistent transient interrupt

Question asked by Rich L on May 17, 2016
Latest reply on May 27, 2016 by Rich L


Hello all,

 

I've created a 'drop test' apparatus which will drop the chip from a consistent height that I set.

I then drop the unit with the chip on it, and change the transient threshold by small decrements until it triggers.

 

However, I'm seeing a lot of inconsistency in whether the interrupt triggers or not - I don't think this has to do with the ODR, as I'm not seeing much change between 100hz and 800hz in respect of consistency.

 

Is there anything that I might be doing wrong in relation to this? I give the transient shock threshold as a mg value/64 (for number of steps).

 

Problem I'm seeing:

if I set it at around (for example) 7000mg , then work my way down until it triggers, I then repeatedly drop it at this height to ensure that it's being consistent... and it is. Let's say this value is 5000mg for simplicity's sake.

 

I then develop some other code, rebuild, and perform the drop test again.

 

Expected behaviour - it should trigger first time.

Actual behaviour - the trigger threshold has moved, and I need to find it again.

 

 

What could be causing this behaviour? Is it a calibration issue?

I know these aren't high precision sensors, but surely there should be some degree of consistency here?

 

Please help... really stumped and not sure if it's something I haven't done correctly, or the sensor...

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