Incremental Encoder with 9411 Board

[AndyLL]

We are trying to use an incremental encoder with the 9411 board. The difference between the inputs A and Ā never goes negative. So, for example, the difference will vary between 3 and 18V. This is also true of B and Ḃ. The specification of the 6411 board suggests that to detect a negative going pulse, the difference has to go negative. Is this correct ? if it is, can anyone suggest a way to read this encoder, or failing that, any product that would convert the signals to something more easy to read?

[SteveD123]

I would use an opto-isolator to get the signals to the levels you want. I have found these Phoenix Contact units useful : http://media.digikey.com/pdf/Data%20Sheets/Phoenix%20Contact%20PDFs/2964555.pdf Note that these are good up to 100 kHz; many other types are only good to 10 Hz. If your signal is above 100 kHz then I have no easy solution.

Just use a voltage divider to cut the 15 V difference on the input down to the 5V the unit is expecting.

We are currently using these successfully on a PCIe 6321 card.

[AndyLL]

Thanks for the reply. However the signal level is not a problem. There are many devices out there that will convert the encoder output to something else. The problem is that the 9411 board expects a logic zero to be between MINUS 300mV and MINUS 24V. A logical one is between PLUS 300mV and PLUS 24V. Therefore, the output from the encoder (or converter) has to go positive AND negative. I cannot find a board that does that. I can't believe that the NI board is so different from any encoder that is generally available. How do people use this board to read an encoder using the differential inputs? Has anyone had any success?

[kwilcox2013]

I'm glad I found this thread. I was about to buy a 9411 module to read my US Digital E6 differential encoder. I was looking at the input spec's for the 9411 and thought it was kind of odd that the expected input on the low range was -300 mV to -24 V. 

What did you end up doing?

[Emach]

Andy,

Just stumbled upon this thread. Have a similar problem reading a BEI HS35 encoder. What you can do is setup a -12 VDC supply and then feed that to the Phoenix Contact unit to handle the A bar and B bar. As long as both supplies (the +12VDC handling and A and B channels and the -12VDC handling the compliments) are referenced to the same ground you should be OK.