Accelerometer Questions

Hello,

I know the 'g' means the magnitude of acceleration. However, when do I use 2g, 4g, 8g, or 16g? Also what do the units mg/LSB mean? How does the conversion work?

I apologize if this is a stupid question. I can't seem to find a good explanation anywhere.

Thanks.

I'm not sure I understand the first question, but I can help with the second one.

mg/LSB stands for milli-G's per Least Significant Bit. As a milliliter is to a liter, 1 mG is to a G. So, 1 mG = 0.001 G's of acceleration. LSB relates to the digital representation of the measured acceleration. This basically tells you the accuracy of your output reading. In other words, if the accelerometer has a rating for 3 mG/LSB, then when the lowest order bit in your output changes, your acceleration has changed by 0.003 G's, or 3 mG.

You have to know the magnitude of the acceleration you are trying to measure. If you don't you will either have to do some research or calculations. If you are trying to measure impact forces, they can be in the 100's of g's. If it is vibration or navigation related, it will likely be less than 10g.

The unit mg/LSB is milli G's per Least Significant Bit. Take, for example, an accelerometer that measures +/- 2gs, and sends out a 10-bit signed value to represent that measurement range of 4g. 10 bits will give 1023 measurement bins, so each bit of the output value represents 4/1023, or .0039g (3.9 mg). An example sensor output chart might be:

0000000000 = 0 g
0000000001 = .0039g
0000000010 = .0078g
0000000011 = .0117g

and so on. As you can see, each time the Least Significant Bit changes in the output the measurement goes up by 3.9 mg. Hence the term 3.9mg/LSB


Hope that helps.

r.b.

---------- Post added at 22:54 ---------- Previous post was at 22:53 ----------

Ooops, enjunear posted while I was typing!

What he said.

r.b.

rberek said:

Ooops, enjunear posted while I was typing!
What he said.
r.b.

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Great minds think alike :-D

I thought it was "fools seldom differ" ;-)