Find reference move in 7344?

[bgrain]

Hi
   I am using 7344 for my system ,I have encountered some questions during the find reference move.

First,it s said  in the hardwar user manual that the index signal can be detected when phase A and phase B are low,
but in my system I can detect the index signal while phase A and phase B are both set active-high in the find reference setting in MAX(because,during the find reference move the reference found become true.)

Second,during the reference move ,I use the NI example "find reference move with position monitor".After its reference found flag become true,I read the current position.But when I  run the find reference move again ,it completes quickly,and the position I read back have been changed. I run the program for the third time it still complete quickly,but the position is same to the second one.This lasts for several times,for the later times the position value doesn't change. I am confused that if it can capture the index signal accurately,how to explain this case?

Third,during a find reference move  there  would be a overshoot,and it will drive the motor come to the captured position,I wonder if it is achieved by servo control.if so when my PID parameters is not optimal   then it is possible that the motor can not come to the exact position.If not servo control how to do that?
Moreover in my system during the servo control I must  send the real absolute position to the drivers for its vector control.That means before I successfully find the absolute position  I can not give the drive a optimal position, and this will affect the control precision.

     Hope your reply !!!
Thank you!!

[Buechsenschuetz]

The phase relationship between enc phase A, phase B and index as indicated in the hardware manual applies for users of software release 6.x only. In 7.x you can set the phase relationship in the encoder setting dialogue of MAX. There you can define the state of phase A, phase B and also of the index pulse (now it can be defined as active low or high - formerly it had to be active low).

If there are any problems I would suggest using a three-channel scope or logic analyzer to detect the actual state of the lines when the index pulse is active, and do the settings in MAX accordingly. Usually problems during the find index move disappear as soon as the settings are correct.

[bgrain]

HI

   Now my PID parameters can make my system move to the desired position accurately,so I can accurately move to where the index signal appears.But when I set the KI to 0(This can not assure the system move to the desired position),  it can not move to the captured position.So the absolute position I get is not accurate. I wonder if  the "find reference move" is accurately realized by servo control or other method. I hope it had better have a  method to find the reference without the servo precision,because my servo control must give the drivers

absolute position values in a real time,which means before I fine the reference I can't get a optimal servo control.Under such a situation I may not get the true reference!!