Osilloscope to check encoder

[buffalonymann]

181116-1035 EST

buffalonymann:

Were your measurements relative to common?

Relative to common, when fully stopped and stable in position, I would expect A+ relative to common to be somewhere near +5 or near 0. Near might mean +3.5 to +5, or 0 to 1.5+ .

Same would be true for B or Z. The receiving detector will look at the difference between A+ and A-. If slightly above a 0 difference that is one binary state, and if slightly below 0 difference that is the opposite binary state. This is called a balanced line system and has good immunity to common mode noise.

If both A+ and A- are +5 relative to common when the encoder is stable, then there is an internal problem. And with B+ and B- both at 2.5 V relative to common there is a different kind of problem.

If you monitor A+ relative to common and rotate the encoder is there any voltage change. I might expect somewhere near 2.5 V. Same check on A- relative to common.

I will be gone until late afternoon. There should be others that can help you.

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I ended up cutting the encoder cable to about 5 ft long, used a 10k ohm pullup resistor across COMM and A+, used a power supply to power the encoder, and I was able to see the pulses. I suspect the encoder cable is damaged someplace along the route causing the issue.

 

[gar]

181119-1556 EST

buffalonymann:

Your description is not of a pull-up resistor, but rather a pull-down.

I doubt that the 1 k resistor was necessary. My guess is that outputs are of the totem pole type.

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[ELA]

Line Driver - this terms requires a further qualifier to best define

Line Driver - this terms requires a further qualifier to best define

The term: "Line Driver" by itself is not really all that specific in terms of the actual output driver configuration. They are not always totem pole outputs.

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z0000019MXOSA2

 

[gar]

181119-2332 EST

ELA:

Other than National Instruments most IC manufacturers seem to define a line driver as having a push-pull (totem pole) output. And more generally a line driver is defined as a driver to extend communication distance over a given cable, and this of course requires the push-pull circuit to obtain a low impedance for both 1s and 0s. A single ended circuit does not achieve this without a large waste of power and require a larger switching transistor.

I did not find a concrete definition of line driver other than at the National site. National's definition does not correspond with the usage of IC manufacturers.

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