1756-HSC/B Totalizer update rate??

[Paul351W]

I am using an HSC/B card to measure a speed wheel with a powered bidirectional pickup. I am using Encoder X4 mode and using the Totalizer tag to give me frequency in order to calculate RPM.

The speed signal I am getting back from the card appears to be reading and be accurate, but when I change speed, the signal has a lot of "stair steps" when I trend the speed in RsLogix5000. The size of the stair step depends on the rate of change in speed, but the time between steps seems to stay pretty constant.

I did another graph of the Timestamp data field, and it does not display the stair steps that the Totalizer tag does.

The instruction manual for the HSC does not indicate that there are any settings for how frequency is determined in encoder mode, does anyone have any other information/ideas?

 

[Paul351W]

Did some more testing, and got a screen shot of the behavior. The red trace is input speed to an eddy current coupling, and the light blue trace is the calculated output speed that I am getting via the HSC/B card.

I am trying to use the light blue trace as a PV for a speed control PID, which is currently not working well on speed changes.