My controller dosent get the feedback

[sumitha]

hi
I have the tachometer of my machine connected to the servo motor but still my controller doesnt recieve the feedback.What should I do ?The encoder settings are enabled.Pls help.

[tst]

Post more details. Which hardware do you use? How is it connected? What are you trying to accomplish? Post your code.

[sumitha]

hi
Thanx for ur response.
I am trying to contorl the speed of an apparatus called clinostat.I am using the PCI 7342 controller and MID 7652 servo motor drive and LABview 7.1.I ve made the connections between the motor and drive and controller.I am able to make the motor run with the help of the motion assistant.But the feedback from the tachometer in the motor is not got by the controller back.Pls do tell me what i am supposed to do .thank you.

[AnalogKid2DigitalMan]

A tachometer is different from an encoder. Tachometer is a single output channel used to measure speed (ie so many pulses per rev) while an encoder has 2 or 3 channels (A, B, and ZIindex)) to determine position and direction. Are you sure the motor has an encoder, is it getting power and are the channels wired up to the controller correctly. Is the software set up for the proper direction phasing and counts/rev for the channels. Without any more details on your motor hardware/encoder and software setup, cannot guess as to what else could be amiss.

[sumitha]

I am sure that there is a tachometer in the instrument.I ve got two hardware devices.
1.PCI 7342
2.PXI .
Is there anything that i have to do with the PXI?
PLs help

[AnalogKid2DigitalMan]

Sorry Sumitha, need more details than that to help further. Have you read all the documentation and troubleshooting for starters?

[sumitha]

Hi
I am sorry for not giving you the full details.But lemme try telling u the whole setup.I ve got a instrument called "clinostat"This instrument has got two motors in it and these two motors control the speed of two wheels.
I am using the PCI 7342 controller and PXI.I am using a Servo motor.There is an option in this PXI and it says:Identify the device:Shud that be done?It says that you will have a file attached to the device file where i can get the identification number but i cudnt find anything of that sort.I am using the Motion assistant s/w and labview 7.1.
With the help of the motion assistant I am able to run the motors now but the motor doesnt run at the speed i set in the motion assistant.why is that so?And I wanted to check whether the analog feedback that comes from my instrument's tachometer(there is no encoder in the machine) is right, I ran a example program "Automatic analog feedback" from the www.ni.com site .My motor runs at a constant speeed and the expected feeedback was totally different from the actual feedback.So the feedback isnt coming properly from the tachometer to controller.Do I need a interpolator to use analog signal with NI motion controller?I am sorry for asking you so many questions but all this harware stuff is something new to me.Pls do suggest me the stuff i shud read to solve all these issues.Thanx a lot for helping me. Awaiting your reply.
Bye-Sumitha

[ColinAE]

Hello Sumitha.

As some of the previous posts have been saying, you will actually need to have position feedback for use with our motion controllers. Your analog tachometer feedback provides velocity feedback, which is not properly interpreted by the PID control loop. I am not sure exactly what behavior you are seeing in motion assistant, as I would expect you to never be able to get the system stable and tuned in order to move.

Unfortuntately, I want to again emphasize that you will need position feedback, such as an encoder or an analog position sensor to use our servo control.

Regards,
Colin C.
Applications Engineering

[sumitha]

hi
I ve attached a diagram(final copy) of the connections that i ve made.
And about the behaviour of my motion assistant -The velocity input
given in the motion assistant is not the input the motor takes,because it
keeps running at a differnt speed rather than the given Velocity input.
So i ran a example program from the www.ni.com "automatic analog
feedback."
When i ran this program in labview the expected profile was different
from the actual profile. I have enclosed the programs output.
I am really struck.
Pls do help me

[sumitha]

automatic analog feedback output.bmp