AD2S1210 emulated encoder question

Hello,

I have been searching the ADI Engineering Zone but could not find my specific question, so I am posting it here and hope to get some answers very soon.

My setup:

I have the AD2S1210 eval board.

from this, i am able to run and confirm on waveform that the default 10KHz excitation signal is good.

I used A1,A0 pin to put this device into normal velocity mode.

i configured digital Res1/Res0 pins to be 00 (10-bit) which according to the spec, i should be able to do so because i am in normal mode.

i do not have parallel bus and SPI is too slow for 10 KHz loop, so i decided to use emulated encoder output, A, B, and NM, feeding this to C2000 eQEP module.

i am to confirmed that the max P2P of differential signal of Sine to SineLo is less than 4v.  so it is all good there.

Question:

1- w/o SPI or parallel bus configuration, the spec said that the Encoder output resolution will be force encoder output resolution to be the same as digital resolution which is 10.  Is it correct?

    " If the AD2S1210 is configured
such that the resolution of the encoder emulation outputs is
higher than the resolution of the digital outputs, the AD2S1210
internally overrides this configuration"

2- assume the answer to #1 is true.  My motor is specified to run up to max 8000 rpm, 4 pole-pair.  however, our application will only run max at 500 RPM.  with 10-bit resolution, how do i determine the number of encoder lines?  is it 256 line in 10-bit resolution?  my resolver has 3 coils (sine, cosine, and excitation) and resolver is mounted directly at back of motor.  What is the correct number of encoder output line for 10-bit emulation?  I am confused on why we divide by 4 to get number of 256 lines for 10-bit resolution?

Thanks,

Henry

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  • 0
    •  Analog Employees 
    on Mar 9, 2021 4:05 PM

    Henry,

    With regards to your question in #1 I believe you are correct but I will need to verify with my local setup as it is not a feature I have personally taken advantage of.  For the rest of my response I will assume that this is correct and that the output will behave as a 10-bit output as desired.

    (NOTE:  I just checked with a colleague who has a setup and unfortunately our Signal Standard is damaged so it may be some time before we get confirmation.  I will however follow-up to confirm as soon as possible.)

    With regards to your question the number of encoder pulses will be 256 because the output is what is referred to as X4 Encoded.  That is to state that the placement of each edge of the A/B pair is counted to arrive at the full resolution (256 * 4 = 1024 = 2^10) for the given selection.  Hopefully this clarifies the confusion and allows you to proceed.   Obviously the encoder increment is a function of position so you'll need to infer velocity as a number of pulses or edges (depending on how you count) versus a fixed evaluation period.

    Sean

  • Hi Sean,

    thank you for the clarification.  This helps.

    another question is about the eval software.  i just order the Eval-sDP-CB1Z controller board for full eval of angle result.

    i can not find the CD which came with the eval board and so trying to search ADI website but can not find it.

    can you please share with me the link for the online download of the eval software CD?

    Thanks,

    Henry

  • +1
    •  Analog Employees 
    on Mar 10, 2021 9:07 PM in reply to HenryN

    Henry,

    The evaluation software is available for download from the kit product page here

    https://www.analog.com/en/design-center/evaluation-hardware-and-software/evaluation-boards-kits/EVAL-AD2S1210.html

    Sean

  • Sean,

    Thank you so much.  i am able to download it.

    BTW, i was able to verify that if you set the encoder resolution higher than digital resolution, then AD2S1210 automatically adjust the encoder resolution to match with the digital resolution.  My system using your RDC works fine now.  Thank you so much for your support.  

    Best Regards,

    Henry

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