Hello,
I'm sorry for the dumb questions, but here goes anyway. I am trying to measure wire-feed speed by measuring frequency of an encoder which is connected to a roll in contact with the wire. Ultimately I want to compare different wire-feed mechanisms based on these speed measurements. After a few initial tests I was shocked to see how much the measured speed varies. There are variations due to mechanical inacuracies and probably the measurements are realistic, I just wasn't expecting to see such a jittery graph under no-load conditions. The test mechanism has a PMDC motor driven in closed loop speed control. The encoder on the roller offers 1024 cpr and varies in rotational speed up to 300 rpm.
After reading these two threads https://forums.ni.com/t5/LabVIEW/Reading-encoder-data/m-p/4094609/highlight/true#M1179300 https://forums.ni.com/t5/Counter-Timer/Reading-encoder-data-and-determining-the-RPM/td-p/4096116 I thought I should check my sample rate and timebase. Can I do this with DAQ express? I only see the loop cycle time as an input for sample rate. The lowest possible input here is 1 ms which I believe is 1000 counts per second, right? Can I adjust the timebase?
I guess I'm just looking for a reality check. Performing the test from the other thread, I drove the roll at 5 rpm and measured a maximum deviation from average +/- 30%. This is pretty slow for the motor, so I also tried at 50 rpm which resulted in +/- 32% maximum deviation from average. Both were using 10ms loop cycle, or 100 samples per second.
Thanks