Encoder selection

[Phizzard7]

I have an application where I need to count out lengths of pipe.  After doing some research I found that a quadrature type encoder should be used.  What I don't know is what type of output to use so it's compatable with the CTRIO unit.  Is a Push-Pull type acceptable?  Also will the CTRIO unit automatically count the pulses positive in one direction and negative in the other using only the A and B channel?

Any help would be greatly appreciated!!!!

Thanks

[Tim]

A Push-Pull (or Totem-Pole) is acceptable.  And yes the transitions on the A and B inputs are enough for the CTRIO to know position in both directions. 

Each CTRIO Input Channel (A-B-C-D-COM) can be wired for either Sinking (COM at GND) or Sourcing (COM at V+).  The CTRIO inputs have a full wave bridge that allows the input current to flow in either direction to create the ON state.

Additionally the CTRIO can accept inputs from an Open Collector (NPN type device).  In this case you would wire the COM to V+. 

It can also handle a Line Driver/Open Source-NPN or also a PNP type device that sends positive current to the CTRIO input.  In those cases the COM is wired to GND.  This wiring would also be the preferred way to receive the Push-Pull driver.

Quadrature encoding works on principle that the A and B inputs are 1/4 cycle out of phase.  Hence the "quad" of quadrature.  Direction can be determined by the state of one input as the other transitions.  The CTRIO uses these state conditions to know whether to add or subtract from the current position.
 

[Phizzard7]

Tim,

Thanks for the info. Very helpful.  For my next question I have to go a little more in depth with what I'm doing with my application.  I stated before that I need to count out 100' lengths of pipe.  I'm wrapping the pipe around a rotating drum and I need to stop the machine at 90'.  An operator will then feed stretch wrap in and start the drum again.  The wrap will hold the coil of pipe together when removed from the drum. I then need to stop the machine again at 100'.  The encoder I'm using has a wheel circumference of 6" and 600 pulses/rev . for 1200 pulses/Ft. The machine will be running a max of 200 Ft/min which is 4K pulses per second.  Now to my question.  Could/Should I use the D2-CTRINT module instead of the D2-CTRIO since the interrupt feature on the D2-CTRINT would be an easy way to interrupt the machine cycle? Im using a D2-240 plc processsor BTW.

Thanks again for you help!!!

[Greg]

I can't speak for the D2-CTRINT, but I can speak for the H2-CTRIO, since we designed it. You could configure the H2-CTRIO with a Pulse Profile table that could turn ON one of its outputs at precisely the 90' and 100' points. This output could be used to STOP the machine either directly, or indirectly.

[blglaw]

I am looking at doing something similar.  I need to measure some steel tubing and cut it off.  I want to use a DL-05 PLC and a C-more Micro Graphic Touch panel for the interface to enter in the length that i need that is measured via a 1200 PPR quadrature encoder with a 12" diameter wheel (1 revolution = 1') and a HO-CTRIO module and then count the number of pieces processed.  When the length is reached, i will need to turn of the wire pulling motor until the operator can use a cut-off saw to cut the material, and the restart once the cut-off saw has returned to its resting state.  Will i require any other special equipment that i might have overlooked and do you have any recommendations or suggestions on how to accomplich this?

Thanks,
Bill

[Greg]

The H0-CTRIO can certainly count the pulses coming from your quadrature encoder. And it can be configured for a Pulse Output and have a Preset Table defined in such a way that you can have the Pulse Output fire when a certain length is reached (based on the count of the pulses coming from your encoder). The count in the Preset Table is also editable from ladder logic, and so the C-more could change its value as you want. Furthermore, the Pulse Output of the H0-CTRIO could be fed back to Input C of the H0-CTRIO and be used to reset the counter, or you could just have a Reset programmed into the Preset Table. Unfortunately, the H0-CTRIO only has one Channel and therefore you can only connect a single quadrature encoder to it. If, however, you used only one signal from the quadrature encoder, then you could configure Input A to count the encoder pulses, and Input B could be tied to the H0-CTRIO Pulse Output to count how many times the count reaches the "cut" length, thus effectively counting the number of cuts.

These are general ideas, but not knowing more details of your application, it is hard to say if these ideas are perfectly practical in your case.

Does that help any?

[blglaw]

I was more looking for what equipment i might be missing to set this system up. Do i need the H0-CTRIO too begin with?  Will the PLC work on it's own and read the encoder?  i am only feeding at about 100-200 rpm's, if that.   As far as my application, I have a motor with a DC control box on it  that i want to stop once i reach a preset length of material. I am looking for accuracy is why i am going to an encoder. 

thanks.

[Greg]

Oh, sorry... well, not having done an application like yours myself, I would rather someone else on the forum perhaps give you an answer. The equipment you have named:

DL05
C-more panel
H0-CTRIO

...sounds up to the job to me based on your description. You may want to try posting this question also on Automation Direct's Forum as well.

[blglaw]

Ok...thanks!