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Entry  Wed Aug 15 18:56:46 2012, Yoichi, Update, IOO, MC Servo Transfer Function Measurements MC-Diagram.pngOPLG-10kHz-1MHz.pngSimpleServoDiagram.pngOPTG-100Hz-1kHz.png
    Reply  Thu Aug 16 01:52:52 2012, Yoichi, Update, IOO, MC Servo Transfer Function Measurements 6x
       Reply  Thu Aug 16 05:08:38 2012, Yoichi, Update, IOO, MC Servo Transfer Function Measurements MCBoard1.JPGMCBoard2.JPG
Message ID: 7201     Entry time: Thu Aug 16 01:52:52 2012     In reply to: 7198     Reply to this: 7202
Author: Yoichi 
Type: Update 
Category: IOO 
Subject: MC Servo Transfer Function Measurements 

Quote:

Last night, I took a bunch of TFs with this method. Now I'm analyzing the data to recover the overall gain G. I will post the results later.

 I calculated the MC open loop transfer function with the combination method. For that, I made a circuit model of the MC board (from the input to the output). The transfer function of this circuit is calculated by SPICE (attachment1). Then it is multiplied by the measured transfer function from the output of the MC board to the input of the MC board (attachment 2) to get the overall transfer function.

The result is shown in the attachment 3. The blue curve is the OPLTF measured with the traditional method. The red curve is the combination method described above. There are some discrepancies between the two curves. The ratio of the two curves (Traditional)/(Combination) is plotted in attachment 4. It seems there is a pole(s) missing from my model of the MC board at around 1MHz. This may come from the omitted op-amps in the MC board model (there are so many op-amps which have flat responses below 1MHz and I omitted most of those). Also the MC board includes many generic filter stages to customize the frequency response. I will open the MC board box to examine what is actually implemented on the board. 

At low frequencies, the two curves are similar but the slope is still different.

I also had to add 83dB of gain to the combined TF to match with the traditional one. I will check where does it come from.

The MC board model (Altium project) is attached as attachment 6. The schematic is attachment 5.

Attachment 1: MC_Board_TF.png  81 kB  | Hide | Hide all
MC_Board_TF.png
Attachment 2: OPTG.png  96 kB  | Hide | Hide all
OPTG.png
Attachment 3: OPLG.png  149 kB  | Hide | Hide all
OPLG.png
Attachment 4: Difference.png  115 kB  | Hide | Hide all
Difference.png
Attachment 5: MC_Board.pdf  199 kB  Uploaded Thu Aug 16 02:55:43 2012  | Hide | Hide all
MC_Board.pdf
Attachment 6: MC_Board.zip  1.069 MB  Uploaded Thu Aug 16 02:55:53 2012
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