Testing and Cause of Failure for Encoders and Hall Effect sensors

[ChrisH]

Al,

Let me see if I understand you correctly and maybe you can translate the parts I don't understand into something a lowly mechanical can get his head around.

Originally Posted by Al Skierkiewicz

Seeing as this is a software only device, one must assume that the bandwidth is only what the sound card is capable of handling. Most sound cards are designed to handle an A/D conversion for CD quality audio which means, best case bandwidth of 22kHz with acceptable distortion of an audio signal. Add to that the aliasing of the conversion (dither, noise, approximation, etc.) you may be only able to see real bandwidth in the 15kHz range.

Ok I think you just said the max sample rate would be 15kHz. Since I don't plan measuring the speed of any motors directly, this is probably not an issue. If the signal is cycling that fast I need to do something different.

One must assume that using the line level inputs, a maximum voltage of just over one volt RMS is the upper limit, which would require an input stage with attenuators capable of analyzing the 12 volt plus signal at the output of the speed controller.

I think you said we have to knock the robot's 12V signal down to 1V max. I assume our electricals can handle that. But a hint or so wouldn't hurt

On the plus side, the PWM output is around 2kHz and the limited bandwidth would certainly hide brush noise and other switching by products present when looking at motors. You may not be able to see the raw output of a sensor, particularly one that has an output frequency above the A/D.

One of the things we might want to look at is the PWM output and happily it falls within the likely range of the sound card. However certain sensors might output at a frequency about the range and so not read correctly.

Additionally, the inputs are single ended, where one side of the signal path is computer common. As such anything that is common mode will raise the chassis and ground of the computer to a point that might interfere with normal computing operations.

If we don't do this right, the computer might fry, or at least get confused.

A transformer would be a big help in preventing these currents but needs to be shielded for obvious reasons.

And these obvious reasons might be? and it prevents this how? and just how is the shielding accomplished?

There are other scope accessories that can attach to laptop and desktop computers that may be easier to carry and less expensive than a full up scope.

There are other ways that might be cheaper and lighter than a full up scope. And these might be?


As I mentioned before, we already have a scope, we just never thought it would be useful to drag it with us to a competition. Of course our sensors have been pretty limited as well, so we haven't really needed it.

I think we are in sort of a chicken and egg situation. We don't use sensors because we can't test them when things go wrong, and therefore don't trust them. But since we don't use them we don't develop the knowledge and capabilty to test them. Why test something we don't use? So I guess you could say the goal of this thread is to lay an egg and render the question moot.