Encoder and LS184 Clock Converter Problems

[Ed007]

I am trying to implement position measurements using a 9000 CPR and 1000 CPR encoder and a clock converter chip LS184 but I have trouble obtaining a consistent count with my PCI-6035E DAQ-STC counter. The count does not seem to be correct (9000 counts in one revolution, which is times 4 in X4 mode or 36,000 counts; I am getting around 14,000 and this is not even the same every time), and the count does not return to zero when turning the encoder back to the original position. I had that problem with the direct encoder connection to the counter (A to source, and B to DIO6), and obtained the LS184 clock converter chip to fix the problem. However, it is even worse with the clock converter. I tried different values of the bias r
esistor but the problem was still there. What am I doing wrong?

[rgharrison]

Hi Ed,

The DAQ-STC counter/timer chip on your PCI-6035E card is not your most accurate counter/timer chip to perform encoder measurements. You are better off using a PCI-6601 card which is much more accurate and has real encoder capabilities.

PCI-6601 (w/ NI-TIO Counter/Timer Chip)
http://sine.ni.com/apps/we/nioc.vp?cid=3589〈=US

The reason the NI-TIO chip is better suited for encoder measurements than the DAQ-STC is because of the following (which might also explain some of the difficulties):

1) DAQ-STC can't reset the count after an encoder revolution (NI-TIO can w/ Z-Index line)
2) DAQ-STC only has one encoder measurement mode and that is the 2-pulse encoder measurement mode. The NI-TIO has the X1, X2, X4, 2-pulse

This essentially me
ans that your DAQ-STC will count up when channel A leads B and count down if channel B leads A. There is no reference point, no ability to reset and no filters on the lines to prevent glitches.

What is probably happening in your case is that you are measuring 9,000 pulses in one revolution and you are also measuring glitches on the line which is why you are getting the extra 5,000 counts. The DAQ-STC shipping example programs will give you some insight into programming your E Series counter to make encoder measurements but your errors are more likely caused by the fact that it is just a simple 2-pulse encoder (up/down encoder).

Hope that helps. Have a good day.

Ron

[Ed007]

Hi Ron,
I agree with what you said. I thought, though, that the clock converter chip LS184 should take care of some of the miscounts caused by the line glitches. Supposedly, it can prevent miscounts caused by glitches due to encoder jitter, and stray noise on the line. It also has filters to deal with the noise on A and B input lines. I did not, however, get satisfacotry results using this IC.

Edin

[rgharrison]

So I assume that when you used an oscilloscope on the lines, you saw the stray noise from the chip. Humm...