NI 6602 Support for Differential Encoders

Issue Details

I have an encoder (motion or any other differential encoder) that provides a differential signal, and I would like to perform position measurements with my NI-6602.

Solution

In noisy environments, it is preferable to use an encoder that provides a differential digital signal instead of a single-ended signal as you will achieve greater noise immunity. The NI 6602 does not have differential receivers, it only has single-ended inputs. 

If the differential signal has a 0 to 5 Volt swing, you may be able to use the encoder in a single-ended configuration with the PCI-6602 and connect to just one phase. For instance, you could connect channel (A)+ to the channel A input of the PCI-6602 and not connect channel (A)-. While the differential inputs would offer better signal integrity, the NI 6602 may still work.

Also, if you do try this approach, you would need to be consistent across each output of the encoder. For example, if you use channel (A)+, you would also need to use channel (B)+, and channel (Z)+. 

If differential inputs are absolutely needed, there are alternative options. One option would be using our motion control products that support differential signals. However, they are made for motion systems and therefore have much more included. Another option is to use the NI 9411 with a cRIO or cDAQ chassis which is also a differential digital input module. 

If the NI 6602 must be used then the final option would be to use external components to build the necessary differential to single-ended conversion circuitry. This can be done in the SCB-68 terminal box or on your own custom connector. Attached is a zip file containing a data sheet for a chip that will convert differential to single-ended signals, a sample schematic, and a text file that explains the schematic.