Help needed to measure output of accelerometer - Page 1
Forum section: electronics / projects

author: choppero
author_rank: Newbie
timestamp: November 18, 2014, 03:55:56 pm
content: I have only basic skills in electronics. I am a machinist and gunsmith with a need to test acceleration.I am currently testing different ways to record the difference in recoil of rifles with and without muzzle breaks. I've tried spring resistance on a sled on rails. And a weighted sled without the spring. Both leave me with too much variation shot to shot. I've located Analog Devices ADXL377Z accelerometer that seems to be able to measure up to 10g. I have purchased a SainSmart DDS120 USB scope to record the very small output of this device. It operates on 3V and when switched on has a constant output of around 2+ volts. When force is applied the voltage change is 2 to maybe 15 Mv. I can see changes on my volt meter but not with the scope. Before I send the scope back I'll ask for help. Does the scope have the response time to evaluate a 10 Ms change?

author: Paul Price
author_rank: Super Contributor
timestamp: November 18, 2014, 04:35:05 pm
content: Yes.

author: awallin
author_rank: Frequent Contributor
timestamp: November 18, 2014, 04:42:08 pm
content: You need to get your prefixes and units right in order to communicate effectively.The scope seems fast enough but the AD sensor mentioned has a bandwidth of only 1 kHz. Anything that happens much faster than 1 ms will be missed by the sensor. If it's only a signal-level problem then build a simple op-amp voltage-amplifier with a gain of 10x or so.

author: deephaven
author_rank: Frequent Contributor
timestamp: November 18, 2014, 04:46:20 pm
content: Quote from: choppero on November 18, 2014, 03:55:56 pmI don't think the response time is going to be a problem, but sensitivity might be. I'm not sure what voltage range you are getting out of the sensor - 2.00 V to 0.015 mV or 2.00 V to 2.015 V? First thing is to set the scope to auto triggering so you can always see a display of the input voltage, then tap it on and off the sensor output to see it change. Then permanently connector the sensor and see if you see a change in the scope's horizontal line position when you trigger the sensor. If you get a reasonable movement you can then go ahead with changing the trigger settings to get a waveform capture. If you are using a 10X probe, you can get 10X the sensitivity by directly connecting the output of the sensor to the scope' input.

author: choppero
author_rank: Newbie
timestamp: November 18, 2014, 05:20:04 pm
content: Quote from: awallin on November 18, 2014, 04:42:08 pmYep I'm a gunsmith and I know how hard it is to communicate without the proper lingo. Sorry 'bout that.The scope, from what I gather, should be able to measure a pulse of 5ms (time right?) and a variation in voltage of around 15mv. I see that a USB has a bandwidth of 60MB/s(am I getting this right? Not sarcastic). and the frequency response of the AD is less than what I require which is 25kHz to 50kHz. Now it seems I need a new board. I liked the AD as it has a 200g force rating and it was simple to wire up. Now it's back to sensor selection with enough refresh rate or bandwidth to actually record.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 18, 2014, 06:43:22 pm
content: Try a piezoelectric detector, there are no (digital) filter circuits involved with those. Search how to use them before blowing up your scope.