Encoder Velocity

Hopefully this is an easy one.

I've mounted a Spindle encoder on my mill. It is 500ppr A,B and index. I have connected it to my mesa 7i77 as encoder 3.

If I launch Linuxcnc and view watch the encoder counts in halconfig, it counts 500 for one revolution of the spindle - good. If I then set the spindle going at 1000rpm (already calibrated) and watch the encoder velocity, it varies wildly up and down between -0.05 and -2. I was expecting it to show me rps? Changing the encoder scale will scale the velocity up or down, but the variation when running at a steady speed is still huge.

This is what I have in my .hal for the spindle:

#********************************************************************************
# SPINDLE S
#********************************************************************************
# ---Encoder feedback signals/setup---

setp hm2_5i25.0.encoder.03.counter-mode 1
setp hm2_5i25.0.encoder.03.filter 1
setp hm2_5i25.0.encoder.03.index-invert 0
setp hm2_5i25.0.encoder.03.index-mask 0
setp hm2_5i25.0.encoder.03.index-mask-invert 0
setp hm2_5i25.0.encoder.03.scale 500 #[SPINDLE_9]ENCODER_SCALE

net spindle-position hm2_5i25.0.encoder.03.position => motion.spindle-revs
net spindle-velocity hm2_5i25.0.encoder.03.velocity => motion.spindle-speed-in
net spindle-index-enable hm2_5i25.0.encoder.03.index-enable <=> motion.spindle-index-enable

Not sure what to check?

Thanks in advance, tom.

counter mode should be 0 for quadrature

Hi.

Just tried with mode 0 and it does nothing, not registering any counts..

That likely indicates that the encoder counter is not getting valid A and B signals

I would check that both A and B inputs on the 7I77 toggle and
that the 7I77 encoder input is jumpered properly for the encoder type
(TTL or differential)

Thanks for getting back to me.

All three encoder 3 jumpers are set for differential (RH position ref 7i77 manual).

How can I check if A&B toggle?

When I had it set to count mode 1 (and the 7i77 still jumpered for differential), it counted 500 pulses for one revolution, which means that A&B worked I think?

If it does not count up (and down) in mode 0 there is likely a connection issue

ENC 7I77
A, /B ==> A,/A
/A,B ==> B./B

is a common type of error

velocity will not be valid in count mode 1 (step/dir) with quadrature input

Thank you. I played around with combinations of A, B /A and /B and could only ever get it to either count up or down. B wasn't reading anything, checked my wiring and there was a break in my joint to the encoder plug.

So with that fixed it counts up and down and shows reasonable velocity whilst turning the spindle by hand (now counts 2000/rev). However, when I power the spindle at some speed (500 rpm) it all goes wrong, velocity flicks on and off and it counts sporadically!

Sounds like a noise or interface issue. Noise is usually not an issue with differential
encoder wiring so I would first verify that you have working differential outputs from
your encoder.

You can do this by measuring from A to /A and from B to /B with a DVM
you should measure a minimum of about 3V between them and it should be say +3V and -3V
depending on the encoder position.