[CAD_CAM_EDM_DRO] Re: Major encoder trouble, need advice.

Hello,
Bill, no, noice on the 5V is not good. However, I'm now supplying the
encoder with a separate 5V source and it still doesn't work. Of course, it
could STILL be due the noice on the drives 5V line but then it probably
shouldn't work by changing encoder.

The board is pretty well decoupled (but perhaps not enough....), I'll
definetly try adding a few uF's across the MOSFET drivers and see what
happens.

Jon,
The cable I'm using with the USDigital encoder is supplied by USDigital to
fit this encoder so I think it should be the correct one. It's twisted pair
and each pair is separately shielded with a foil-shiled, all shields are
common, you can see details of it here:
http://www.usdigital.com/products/cables-connectors/cables/6-pin/ca-mic6-sh-
nc/

The cable I'm using with the AMT encoder is an "ordinary" cable with 4
twisted pairs and one braided shield.

The low-level voltage is 0.45V and the high level is 3.4V when using the
SN75115 internal termination only. (That's how I have it right now). The
highlevel is right on specification but the low-level is speced at MAX 0.4V
and I see 0.45V... If I disconnect the encoder from the UHU the low-level is
roughly 20mV and high level is 5.05V.

I tried adding 1k pullups from all four singnals but it made no difference
to the operation and barely any to the voltage levels.

I've measured the risetime to around 25nS with a small ringing so it's
settled around 75nS. There's a slightly larger ringing on the falling edges
than on the rising but it settles in roughly the same time. The specs for
the E7P claims typical ristime of 500nS but ~25-75 is what I see. Perhaps
because I'm using such a short (300mm) cable?

I know you're not too fond of the original UHU and I don't know if you've
looked at the "HP-UHU" although we have discussed it a couple of times. I
don't know how the firmware handles the encoder counting but I guess it's
interrupsdriven.

I can tell you that after getting the drive working with the 3600 line
Hengstler encoder and with the cheap AMT encoder I was NOT expecting this
kind of trouble with a USDigital encoder. And ofcourse USDigital claims
there's nothing wrong with the encoder and I can't proove there is.

Any Renco encoder in particular that you'd recommend? Seems like the RE202
is the only one with differential output that's available for online
purchse. (I'd hate to throw more money on this though without knowing it'll
work....)

Thank you all, it is very much appreciated!
/Henrik.


-----Original message-----

Hi Henrik,

Noise on the 5V rail is not good, as such noise will affect the circuits
connected to it.

I have seen this problem before wherein the driver circuits were not
capacitively decoupled very close to the driver circuits themselves. Adding
a 10Kuf cap to the 5V rail circuit I was working with did not help, but
adding 10uf tantalum caps right across the driver circuits solved the
problem. The drivers draw a lot of current, and unless they have a cap
close by to supply the electrons, the rest of the circuit will be
compromised.

Regards, Bill N