potentiometer position delay

[immortalc]

Hi I have an electronics question.

I have a mechanical swing arm that I have attached sensors such as torque and positon sensors.  I'm using USB-6212 and labview 7.1 to record the signals.

the position sensor is a single turn 5k pot that powered by a 5V regulator and the wiper goes to the AI.

I noticed that there is a signal delay about 20ms from the pot with resepect to the torque signal and when I start to swing the arm.  Positon and torque should start to change at the same time.  Do you know if there is anything electrically that might be causing this 20ms pot delay?  I'm swinging this arm about 0 to 90 deg back and forwards at about 1-3 Hz frequency.  the higher the speed the delay increases. 

Thanks,

Tony

[Kristen_K.]

Hi Tony,

Are your sensors mounted in the same area?  Is the delay just in the begining or does it look like the entire position sensor data is shifted by 20 ms? A screen shot of what you are describing will probably answer that question!  The part that is the most curious to me is that the delay increases with higher speeds.  If it were an issue with the pot's resolution, I would expect the delay behavior would be the opposite: higher speeds, less delay.

Kristen H.

[immortalc]

thanks for your reply.  The position sensor is further down the line of the bend axis but the position is geared 1:1 to the torque sensor so it shouldn't have a delay effect by a lot? I just wanted to double check if there were any other electrical issues that could be causing the delay.  I think its now more a mechanical delay?  The graph i'm showing seems to match up when the signals come together at the end of each cycle but there is a noticable delay at the begging and the peaks.  the x-axis is time in seconds.  You can see where the rise of the position signal in each cycle doesn't occurs slightly after the torque signal too.

Message Edited by immortalc on 09-16-2009 12:18 PM

[Kristen_K.]

Hi Tony,

I was thinking about this a bit more, and I'm not a physicist by any means, but I think it makes sense to have position lag.  Because of inertia/momentum the torque would have to "build" a bit before the intertia due to the mass of the arm is overcome and movement begins.  Likewise, torque would dissipate but momentum would cause the arm to continue moving a bit longer.  Therefore, I believe the delay your seeing is not likely electrical, but rather mechanical, as you suspected.

Do you agree?  

Kristen H. 

Message Edited by Kristen H. on 09-18-2009 08:25 AM