NI 9505 current sensor sensibility

[cornucopiae]

Hello;
I have a NI 9505 brushed DC servo drive module. I am controlling a small DC motor (its max continuous current is 1 Amps); I pretty much followed the current loop example code I found for closing the current loop and generate the PWM signal. The only thing I added is the interface to a CAN bus. When the current set point is above 0.5 Amps eveything works just fine; the current goes to the commanded values and oscillates around the set point of 2-3 levels. I have problems with lower currents; for values below 0.5 Amps the reading of the sensor seems currupted by a lot of noise. I don't think it is a problem with the current loop; even if I cut the loop and apply 0V to the motor, I get a 60 levels noise on the current; which is around 0.35 Amps.

I cannot find out if I did something wrong or if I can't avoid that noise. Maybe the sensor was designed to work with higher current (after all it can measure up to 12 Amps) and it loses precision around 0 Amps. Has anybody had the same problem?

Thanks for your help.

    M.

[cornucopiae]

I was wrong, when the current loop is cut the problem goes away. It was caused by the fact the the PWM minimum pulse width is 2ns. My motor resistance is so small that in order to have currents smaller than 0.5 Amps; I need duty cycles below that value. The integrator did the rest.

Sorry my first post was wrong.

Thanks you anyway.

M.