Determine acceleretion sensitivity for accelerometer

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Hello,
I am trying to determine the sensitivity of an accelerometer based on recordings from another accelerometer. I have previously been making recordings with an old wired accelerometer, but am now wanting to go wireless and want to ensure then the new accelerometer is good enough to replace the old.
The new accelerometer is an ADXL354 (analog) from Analog Devices (ADXL354 datasheet), coupled to a Shimmer IMU device (Shimmer IMU spec sheet) via the Shimmer PROTO3 mini expansion board (PROTO3 spec sheet). I do not know the specs of the old accelerometer.
I have conducted a shaker test with the ADXL354 and the old accelerometer. I keep the amplitude of the shaker constant at an arbitary value, and sweep in frequencies like 20-300-500-800-1000 Hz, then turn up the amp a little an sweep back down. (fig 1) The sample frequency of the old accelerometer is 5000Hz, while the ADXL354 is limited to 2048Hz by the Shimmer IMU. I know the old accelerometer outputs in volts, and if I understand correctly the ADXL354 outputs in mV as per the datasheet specifying the ADXL354's (typical) sensitivity as 400 mV/g?
The x-axis are not aligned as I cannot start the recordings for both accelerometers simultaneously, but I have panned the recordings to match in time.
My problem occur when I want to convert the accelerometer output from V to g. I have been given a factor (0.0176*1.1) to multiply the old accelerometer recording with to convert its output to g. I then want to convert the ADXL354 output to g and I divide by 400 as per its sensitivity. However, when I do this the acceleration for each accelerometer does not match. (fig 2)
Summed up my question is; how can I correctly match the measured acceleration of a new accelerometer to an old one to ensure that the new accelerometer is sensitive/good enough to make recordings of equal quality as the old accelerometer.
I have attached the data I have recorded for the two accelerometers and the script I use for plotting if anyone is interested.
Edit: ops, at first try I didn't get the old acc data attached as is was larger than 5MB. I have now divided it into two tables which should be merged when running the script.
  8 Comments
Dams
Dams on 17 Nov 2020
Edited: Dams on 17 Nov 2020
Hello,
I am sorry if I have not been clear on the matter but every test have been conducted with both accelerometers mounted on the same shaker at the same time. The reason for the difference in registred recording times is because I cannot start the recording for the accelerometers at the same time since they run from two different programs (LabScribe and Shimmer Consensys).
I have conducted a third test using a different 'old' accelerometer for comparison. This accelerometer is static (DC) and I can now correctly compare the two accelerometers. The problem was as you suggested, Mathieu NOE, that I was trying to compare an AC to a DC accelerometer measurement.
Thank you for you help and time.
Edit: Mathieu NOE, I wold like to accept your answer as the answer to my question but I cannot since you have only commented on my question. Would you copy your comment from November 3rd and post it as an answer so I can accept it?
Mathieu NOE
Mathieu NOE on 17 Nov 2020
hello
will do !
hope you get through the testing activities !
all the best

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Accepted Answer

Mathieu NOE
Mathieu NOE on 17 Nov 2020
hello
the ADXL specs says the bandwith is 0 to 1500 Hz. The mems accels do measure static (gravity), so make sure you have not issue by reading static + dynamic data on the ADXL plot and compare with (for example) a piezo accel that have typically bandwith between 5 Hz to 5 kHz at least (NB here NO dc value can be measured)
so depending of accel technology (mems / piezo / voice coil) look at static performance also if your acquisition is DC or AC coupled

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