Single-ended or differential signal from motor

[MartinP]

We are using a brushless DC servomotor (4490H024B) in combination with a three channel digital output encoder (IE3-1024L ) from Faulhaber.

We want to connect the A, B and I lines of encoder (IE3-1024L) to a single ended data acquisition device 9402 from National Instruments.

Can we assume that we can safely for the encoder leave out inverted lines of A, B and I floated, i.e. not connected anywhere?

From the data sheet of the encoder we are not entirely sure whether the encoder signals HAVE to be always read differentially or not.

If they HAVE to be read differentially, we might need to switch to another module, e.g. 9361 from NI that can read differential signals.

Figure: Circuit diagram of the encoder.

[dboels]

Hi Martin,

You always need a reference to measure to, or a ground or another point in the circuit. In you're case you'll be measuring referenced to the A', B' and I'.  Leaving them out would mean you need another reference point, which could be the ground, but they recommend to measure differentialy, to reject noise and ambient interference.

So as you have floating sources (not referenced to the ground), you won't be able to make a succesful measurement with the NI 9402 (which are all single ended measurements, referenced to the same ground in the module).

There are other possibilities for you then the NI 9369, for example NI 9411 and NI 9435 (slow)

Dieter

[Buechsenschuetz]

There is also a break-out box from NI (do not remember the designator) which allows for connecting both differential and single-ended signals to FlexMotion boards. 

[Highland_Controls]

You should be able to do this fine, as long as the distances aren't too great or there isn't much noise.  Connect the grounds of the 9402 to the common(0V) of the encoder.  Just make them reference the same point.