Re: [TCML] BPS Testing

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Hi Terry,

I've noticed this problem also with measuring motor currents. Inductive 
loads seem to cause problems. The manufacturer is well aware of the 
problem as well. I've talked to the engineers at dataq and they 
mentioned the usb is the absolute worst for this problem. All they could 
offer was to ensure the pc chassis is grounded to the DC power supply 
and acquisition device. I've tried RC filters with motor current 
measuring but it didn't make a difference (even chassis grounding didn't 
help). I'm using shielded cable as well including the USB which I bought 
a shielded USB cable from BlackBox. No change however. In most cases, I 
can run several hours before this problem occurs. But with the TC, only 
a few seconds. I also ran through a filter to the input of the NST 
(didn't help).

Something I'm going to try is to ground every digital and analog input, 
recording input, event input, etc. (and maybe even build a small 
shielded box around the device). The device is pretty small (about 2.5" 
x 2" x 1"). It's a cute little device and does do a great job (except 
when this problem occurs, and has been the only problem I've found with 
the device). I do like the fact that I can record data up until my hard 
drive is full (so hundreds of gig of data if so desired). Digital inputs 
are 5V but the 4 analog inputs are 200Vp.

Thanks for the thought.
Bart


piranha wrote:
> Hi Bart,
>
> Maybe do a DFFT thing to find the base frequency of the signal of 
> interest and then sample at the 2X Nyquist rate.  A simple RC filter 
> might also turn the very fast "spike" into a "bump" that would be 
> easier for the toys to pick up out of the noise.
>
> Just a thought...
> Terry
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