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wiring a quadrature encoder


I am trying to use a quadrature encoder to measure the speed of a motor. I have a cRIO 9072, NI 9401, and following encoder:


I am new to all these equipment. So first of all I am trying to find out how to wire everthing together. I have read the tutorial on the NI website about quadrature encoders. But it doesn't really talk about wiring everything together. So here are my questions: 


1: What does NC, COM stand for. What should I be connecting to the NC and COM pins.


2: I am guessing I will have to use 2 channels like DIO1 and DIO2 to read the encoder data (i.e.output A and output B). Is that correct.


3.  The encoder also requires a 5V source. Can I somehow use cRIO for this or do I have to use someother external power source.


4. There are 5 pins on the encoder viz Output A, B, 5V power, Ground and No contact. I am thinking the NC goes no contact and COM goes to Ground. The question here is if I will be using 2 channels on the 9401 do I have to connect NC and COM for both channels to the  pins on the encoder. Or once will suffice.


5. Once I have everthing is connected, I have to exampe to work on the programing for it. But I am not sure how to get velocity from the encoders. None of the tutorials mention velocity, they all talk about only the position.


Please excuse me for such basic questions. But I am not familiar with electronics


Thank you



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Message 1 of 5

Hi Sid,


1.  NC = no connection, COM = common (a common reference for ground)


2.  Absolutely


3.  You're not going to be able to get a good power source out of the module (see the specs for current you can source), so go ahead and look for an external supply.


4.  NC goes nowhere, and COM goes to ground.  There is no isolation between digital lines on this module, so all COM pins are already connected.  This means you only have to connect ground to COM once.


5.  What you will read directly from the encoder will be position.  If you want velocity, divide distance moved by time!  Or check this tutorial out.


I hope this helps!



Brian A.
National Instruments
Applications Engineer
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Message 2 of 5



Thank you very much for your reply.


I have couple of more questions. It would be great if you can help me out with them.


1. I will be using a DC power supply to get the 5V needed for the encoder. So, I will connect the +ve terminal of the supply to the to the encoder. But what do I do with the -ve terminal of the supply. Do I leave it unconnected or the DC power supply also has a ground, so should I just connect the -ve to the ground. 


2. As I mentioned earlier, the power supply has a ground too. So,should I connect the ground from the encoder to the Digital I/O - COM or should I connect it to the ground of the power supply.


As you can see, I am kind of lost here. Please help me out


Thank you


Siddhant Shah

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Message 3 of 5



1. Yes, connect -ve to ground.

2. You can tie all the grounds (COMS) together

- Hunter

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Message 4 of 5
siddant, Do you need to measure instaneous velocity at very small angular intervals? If not, you may only need to use one channel of the encoder.
Labview 8.5
Meas Studio 2008
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Message 5 of 5