Accelerometer selection for both very low and very high speed

hello,

I found that ADXL377 would be the best option for high g measurements upto +/- 200g. However my application involves both very lowg(+/-1g) and very high g(upto 180g) detection.

My questions:

  1. Will the ADXL377 will be inefficient to measure low g values like very small movements?

  2. If using two different acceleration (lowg and high g based) would solve this issue?

  3. What can be better options for this scenarios?

Thank you for your suggestions.

Maybe two accelerometers are required for that. One set for high G, and one for low G.

edit: Like a ADXL377 for high G, and a ADXL337 for low G.

But, there would be no damage for ADXL337 incase of high g (for example 200g) or any failure ??

I agree with SurferTim.
A range of 1 G and 200 G is not very big. A 16-bit accelerometer should easily measure both. But almost no accelerometer is really 16-bit and noise is a problem.
The ADX337 will break at 10000 G, you may use it at 200 G, but above 3 G the values are probably clipping and not useful anymore.

I'm getting a HDR photo feeling. A single HDR photo can be made out of a few photos with different exposures. A calculation is performed to avoid the clipping of the over-exposure and under-exposure of the photos.
Would something like that be possible to get a single high range accelerometer result by using two (or more) accelerometers ?

Peter_n:
The ADX337 will break at 10000 G, you may use it at 200 G, but above 3 G the values are probably clipping and not useful anymore.

I would read the ADXL337 until it started clipping at the high or low range limit, then go to the ADXL377 until the G force is back in the range of the ADXL337.

Thank you very much for your reply and suggestions.

May i ask you one more question!

If the two Accelerometer are two be fixed on a wheel which is moving at 160 KMPH, if i kept the ADXL337 (lowg) near to the centre of wheel, will it not have always low g values?

If we go away from the centre then the net acceleration will increase, which may go till 170g(depending on radius)?

Will this method be correct, to put the ADXL 337 near to centre and ADXL 377 nclose to the perimeter?

What else should i care about?

They are accelerometers. When such a sensor is near the centre, there will be a strong rotation. Perhaps the sensor will go nuts because of the rotation. I don't know.

Do you want to measure the forces on the wheel, or the road below it ?
To measure the road below it will be hard, since the forces of the rotating wheel are so big.

Accellerometers are sensitive for vibrations and shocks. If that wheel is on a road, you will measure massive vibrations and shocks, with higher G values than 3 G or 200 G.

This is typical something that you have to try for real.

I have to calculate the speed from accelerometer implementing on wheels of a train(simply prototype may not go till real scenario ) and most important is to detect the standstill position (for this i need LOW G ACC) correctly. I would also like to calculate the speed when it is moving (for that i need HIGH G ACC). The maximum speed would be till 180 KMH.

The earth gravity of 1 G is measured when not moving.
I think the 200 G sensor can measure the earth gravity. Some inaccurate or noise can be filtered out in software, perhaps as simple as the average of a few samples.
If you do use two accelerometers, you may attach them both at same spot, or the ADXL337 in the middle. That's all okay, since the ADXL337 is only used for position/angle when the wheel is not moving.

The speed can be calculated when the G forces and the distance to the centre and rotation speed is known.

What if the speed is very high, and the earth gravity can no longer be measured in the data ? Then you don't know the rotation speed of the wheel anymore, and you can't calculate the speed from the G forces.

The best way is to test it. Get a drill (one that can adjust the speed). Attach a small wooden wheel to it. Attach an Arduino and sensor to it. Safety glasses on, and get some real data :stuck_out_tongue:

Did you know there is a special bootloader, that allows for example the very small Arduino Pro Mini (and other Arduino boards) to store data to flash, so you don't need an micro-SD card ?

It depends on the size of the sketch, but it can be up to 25k free storage space. With three 16-bits integers (x,y and z), at a sample rate of 10Hz, that is 7 minutes storage.

"What if the speed is very high, and the earth gravity can no longer be measured in the data ? Then you don't know the rotation speed of the wheel anymore, and you can't calculate the speed from the G forces.."

I am using a ITG-3701 Gyroscope for this purpose , it can give accurate speed up to +/- 4000 DPS. Hopefully it will solve the issue. I have to get it work.

I used arduino for the first time, but i found this forum very helpful. I get very resourceful answers. Thank you guys. :slight_smile: