Quadrature Input and RS422 Signal Levels

[Michael_Wise]

I have a quadrature signal coming from a motion control drive that is in RS422 levels.  What would the easiest solution be to get those signals into the quadrature encoder module (cFP)?

Thanks,

Michael Wise

[Eric A.]

Hi Michael,
Could you elaborate on what you mean by RS422 levels?  It sounds like you have a motion transducer that outputs a RS-422 signal.  What FieldPoint controller and modules do you have?

[Michael_Wise]

http://www.baldor.com/products/motioncontrol/microflex.asp?product.asp?1=1&product=Servo+Controls&fa...

It has a simulated (actual signal to drive is a resolver) quadrature signal coming out.  I'm only concerned with A+B since I'm just using it to determine speed.  In the spec it says the signal levels of the encoder output conform to RS422 Levels.

I was planning on using the NI cFP-QUAD-510 for reading the encoder A/B signals back into the cFP system.

[Eric A.]

Hi Michael,
Thanks for the additional information.  I believe RS-422 voltage levels are 0 to 5 volts which is basically the same as a TTL signal.  If you have a cFP-Quad-510 connected single ended a low signal voltage is between 0v and 0.8v and a high is between 2v and 30v.  Since the motor encoder uses RS-422 voltage levels you should be able to wire the encoder directly to the cFP module.

[Eric A.]

The manual for this module has a lot of information about acceptable voltage levels and different wiring configurations.

[Michael_Wise]

Most places i've read seem to show RS422 at being +/- 7V.  So, I'm not sure how that module would react to a negative voltage.  Obviously, the +7 wouldn't harm it.

[Eric A.]

Hi,
I think you are correct about the voltage levels for RS422.  However I am not sure that your motor controller outputs signals at those levels.  The manual for those controllers only mentions inputs at RS422 levels.  For an output it only says "Simulated encoder output for connection to external motion controller".  I would check with Baldor to see exactly what specifications it has for ouptuts.

[Michael_Wise]

http://www.baldor.com/downloads/manuals/_downloads/MN1919_01-2006.pdf

That document states they are of RS422 levels (pg 44 or 4-10)

[RavensFan]

Do you have this controller now and is it in some operational state?  The easiest solution may be to run it and use an oscilloscope to see what the actual signals coming out are, rather than relying on a document that is somewhat confusing and possibly contradictory.

[Eric A.]

If the controller does indeed output RS422 voltage levels then you will not be able to connect the controller directly to the cFP module.  The specifications for the module state the lines cannot use a negative voltage.  I will do some checking to see what options might be available.  Ravens Fan has a good idea to investigate the signal.  It would help us to know exactly what the situation is.