In the future just reply back to other comments instead of creating a new thread.  That will make it easier to follow.

Lets make sure I understand. 

You have a PC board with 30 leds. 

Power is supplied to each of the LED's via a 30 pin connector. 

The PC board is mounted on an X-Y table

The X-Y table position is controlled by two servos.  Servo positioning is controlled by communication link to PC or PLC?

The OV32T powers and LED.  I am assuming one of the LED's mounted ont the PC board or is this a separate LED?  If PC board LED then is the connection made by moving the board or does each LED have a separate circuit going to the OV32T?

LED is powered by OV32T.  How is spectrometer triggered? also from the OV32T and relay?

Does the PLC control the X-Y table.  if now how does it know the positioning.

Finally, what exactly is your question?  You mention wanting to do one ladder logic step for one LED.  I'm not sure what you are asking.  I can help you with specific programming questions, but nobody is going to write a section of your code for you through a forum.  It it's what I think it is, it should be fairly straight forward and I can help you past where you might be stuck.

Ok, I think I understand what you are doing.  I'm not sure what help you need with "one or two rungs."  I can walk you through how I would go about tackling this.

There needs to be some sort of input to the PLC to let the system know everything is ready and the sequence can start.  Let's assume a pushbutton to an input on the PLC.  Pressing the pushbutton will start a sequence in the PLC.  I would also have a stop pushbutton to allow the sequence to be aborted. 

Sequence:

1.  Send coordinates to servo. 

2.  Wait for feed back from servo that position reached.  If none available then start time delay to allow servo time to get into position.

3.  Power output on OV32T that corresponds to servo position requested to light appropriate LED.

4.  Trigger spectrometer to measure LED

5.  How does PC know spectrometer is sending info for LED?  Spectrometer on?  or output from PLC?  I would add a time delay before taking a reading. 

6.  Increment to next position return to step one until all leds have been lit.

Kind of hard to put rungs in this text but something like this might indicate sequence is running:

    Start     Stop       

-----||-------|\|--------(B3:0/0)   sequence running
           |
-----||---

   B3:0/0 (seqence running seal in)

  sequence        position
   running          complete

----||-----------------|\|---------[ctu]    counter to increment through the different LED's

I think the sequence steps will help you more than the rungs, but maybe they will give you somewhere to start.  Feel free to reply with additional questions.