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ADXL001 noisy output

Dear community users,

at the moment I try to set up a vibration monitoring system using the MEMS accelerometer ADXL001. To "check" the ADXL001 I have just made a small pcb. On this pcb I soldered the ADXL001 and two capacitors. One capacitor at the power supply pin VDD to Ground (0.1uF) and the other one at the Output Pin Xout to Ground with 1000pF=1nF. The power for the ADXL001 is delivered by a linear regulator board with a 7805 fixed regulator. I  have connected 100nF capacitor from input to ground and output to ground of the 7805. My data acquisition board is a DAQ NI-9234 from National Instruments. The samplerate is 51.2k (maximum). My vibration source for the ADXL001 pcb board is a small electrodynamic shaker with sinus excitation.

In the time domain I see a lot of noise on the signal... I have just put the time domain and the FFT of the time signal in the attachment. The data acquisition and signal processing was performed with MATLAB.  Any ideas what to do against the noise ? I actually want to use the ADXL001 up to his 22kHz bandwiths but I get a lot of noise beginning at 1kHz... When I design a low pass / anti aliasing filter, then I have select the cut of frequency at 22kHz.. (lower than the half of the maximum samplerate).

The amplitude in the time domain plot is already calculated in acceleration g with the sensitivity setting of 24.2mV/g  at 5V power supply (refer to ADXL001 datasheet).

Thank you for your help and please apologize my bad english.

attachments.zip
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  • While the ADXL001 does not provide 32kohm of source impedance, you can use an external resistor for the same purpose, by placing it in between the output of the ADXL001 and the 1000 pF capacitor, to introduce a single pole filter at 5kHz.  You stated that you need the entire 22kHz bandwidth, so you may not do this, but we wanted to clarify what you would do, if you wanted to lower the noise by lowering the bandwidth. While we work out the details on how to predict the total noise in a given configuration, you can still work on the original question of: "Is the noise in your original observation the result of actual inertial motion or from the natural noise behaviors of the ADXL001 itself."  In your validation test, you might want to couple your ADXL001 test board to the reference accelerometer and take simultaneous data. Keep in mind that the attachment method can also contribute to differences in the two sensor responses.

    Very best regards,

    NevadaMark

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  • While the ADXL001 does not provide 32kohm of source impedance, you can use an external resistor for the same purpose, by placing it in between the output of the ADXL001 and the 1000 pF capacitor, to introduce a single pole filter at 5kHz.  You stated that you need the entire 22kHz bandwidth, so you may not do this, but we wanted to clarify what you would do, if you wanted to lower the noise by lowering the bandwidth. While we work out the details on how to predict the total noise in a given configuration, you can still work on the original question of: "Is the noise in your original observation the result of actual inertial motion or from the natural noise behaviors of the ADXL001 itself."  In your validation test, you might want to couple your ADXL001 test board to the reference accelerometer and take simultaneous data. Keep in mind that the attachment method can also contribute to differences in the two sensor responses.

    Very best regards,

    NevadaMark

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