Differential line receiver for quadrature encoder into a 660x counter timer?

[atakahas]

Is there an NI module or signal conditioner that will act as a differential line receiver for our incremental rotary encoder?  I don't want to have to build my own out of IC's and would like to have a DIN rail mount module which is presentable to our customer. 

[hoffiz]

Hi Atakahas,

Unfortunately we don’t have any differential to TTL (single ended) signal conditioning card, and since you will probably end up building the circuit it will be better to get a custom DIN rail box. For reference I can point you to this knowledgebase:  where gives you a suggestion on how to build the circuit: How Can I Connect a Differential Encoder to a PCI/PXI-660x?.

All the products that I have found on ni.com for DIN-Rail Accessories are for our own cards like USB devices, TBX connector blocks, etc not for a custom DIN rail that you will probably end up building.

I hope it helps

[atakahas]

Thanks Jaime,

I kind of figured I was going to have to build my own.  Thanks for confirming my suspicions.  Any chance that future models of the 660x will include an option for differential line receiving of differential encoders?

--Andrew Takahashi
kDy Automation Solutions

[hoffiz]

Hi Atakahas,

I was researching if future 660x models will have differential inputs and it seems that not, at least in any time soon. What I will suggest is: “Product Feedback” and I can ensure you that our Research and Development department really takes a look at this suggestion; so making the suggestion would be the right course of action to take.

Regards

Message Edited by Jaime F on 12-11-2007 11:14 AM

[Ethan_Niu]

Hi,

 I saw this KB http://digital.ni.com/public.nsf/allkb/B3945A72AE53D1B086256EF7007C4D0D

 If my encoder is differential output. Which means it has A+,A-,B+,B-,

 According to this KB. I can connect A+B+ and A-B- to different counter to get better accuracy(differential input).

 But I can't find any setting that allow me to bind the two channel together. Or it means if I wire like this. The 660x card will automatically treat the encoder as differential input?

Thanks,

Ethan

[bei chief]

You might consider the BEI Optical Encoder module.  It converts differential line driver signals to the single-ended signals used by NI boards.  We have recommended it to out customers many times with great results.  BEI offers versions compatible with 5V, 12-15V, 24V and open collector encoder outputs, converting them to the NI format.

[anishm]

Will I lose resolution if I use a BEI converter to convert my differential encoder to a single ended encoder that NI cards can accept? 

[Doug_L._Bear]

I don't understand how you would lose resolution on an encoder signal, unless I am misunderstanding the use of resolution.  To me it means the number of encoder pulses per revolution or per inch of movement.  This is a fixed number based on the physical encoder and should not change based on what you read it in with.  If I am mistaken on what you are asking please let me know.

[bei chief]

The optical isolator module acts as a buffer to convert the differential encoder signal to single ended.  It does not effect the resolution.

Here is a link to the optical isolator user guide from the BEI web site:

http://www.beiied.com/PDFs2/oim.pdf

Use the diagram in Connection Instructions #1 with the differential output encoder.  Connect A, B, Z and common to the NI module.  Do not connect module outputs A/, B/ or Z/ (they float).