AD2S1210 resolution setting

Hello

             Customer would like to meet 16000rpm ( 266.6rps). Do you have any suggestion or comments for 12bit or 14 bit resolution that more suitable for this specification?  It looks max rps of 12 bit and 14 bit should meet 266.6 rps. Thank you. 

 

Xtal:8.192Mhz

Pole pair: 4

Speed: 16000rpm (266.6rps)

       

BR

Patrick

Parents
  • +1
    •  Analog Employees 
    on Oct 26, 2020 11:12 AM 4 months ago

    Patrick,

    Can you comment on if the speed quoted already accounts for the speed multiplier of the pole pair (electrical speed) or if it is the mechanical speed of the monitored shaft?  Also is there a requirement for overspeed indication?

    Thanks  

    Sean

  • Hello Sean

                   The speed ex 16000rpm should be mechanical speed. Customer's motor is 4 Pole-Pairs. the resolver is 2 Pole-Pairs. So at motor run  a cycle, we should get SIN/COS speed become double, is it correct? Please refer to below waveform. above pic is  4 Pole-Pairs, below pic is 2 Pole Pairs. 

                    if correct, the motor run one cycle, the resolver get speed from 16000 rpm to 32000 rpm. If consider resolution setting, we need to depend 32000 rpm for our resolution setting, right? 

                     It is a little urgent, so need your help to clarify above questions, Thank you. 

    BR
    Patrick

  • Hello Sean

                 Do you have update for above question? Thank you. 

    BR

    Patrick

  • +1
    •  Analog Employees 
    on Nov 17, 2020 12:58 PM 3 months ago in reply to patrickchen@morrihan.com
      1. Customer's max speed looks 64000RPM. But encoder read speed can not meet 64000 RMP, right? Has any suggestion for encoder ex : has feature to divide max 64000RPM....

    Patrick you have two choices with respect to the encoder output to extend the range.  Firstly if you have already increased the master clock rate of the device then the max rotational frequency also increases proportional to that change as it does in the position/velocity reading case.   Second, you could alternatively change the resolution to 10-bit mode and extend the maximum rotational velocity through the mode change.

        2. While measure 160000 RPM via encoder interface, There are different  PWM width as below waveform, Is it normal? What is the root cause for this phenomenon? 

    This appears to be related to velocity ripple in your system configuration.

                      3. The encoder description looks less on datasheet. What is max RPM support by encoder? It looks has only resolution for setting, right? If any document of encoder description, it will be better. Thank you. 

    The encoder description is very sparse in the datasheet but you can assume the same dynamics for all resolution modes as with the primary data-path as they share the same source.  We are actually in the process of reviewing our training collateral for this product family and this will be valuable feedback to help us improve the support for this product.

  • Hello Sean

                For velocity ripple issue to cause encoder different pulse width, customer testing it on Hill and environment should be clean. . But while above 40000RPM speed, encoder signal will happen this issue. Do you have any suggestion for it? Thank you.  

    Speed: 40000RPM

    Ch2: AD2S1210  Sin

    Ch3: AD2S1210 Encoder A

    BR

    Patrick

  • +1
    •  Analog Employees 
    on Nov 20, 2020 12:59 PM 3 months ago in reply to patrickchen@morrihan.com

    Patrick,

    Please let me clarify that I was not suggesting the velocity ripple was generated outside the chip.  Instead there is a specified amount of ripple that will exist in the application as a function of incomplete rejection of the carrier through the tracking loop.  This error is specified in the datasheet in the Velocity Accuracy section (see note 4).

    Sean

  • Thank you Sean,

    But customer run 50000~64000RPM and analysis A、B、NM signal via encoder interface. They find out the error achieve 10% at 60000RPM not only several LSB error. So it looks unreasonable. Do you have any comments for these error while run 60000RPM via encoder interface? Thank you. 

    BR

    Patrick

Reply Children
  • 0
    •  Analog Employees 
    on Nov 24, 2020 2:44 AM 3 months ago in reply to patrickchen@morrihan.com

    Patrick,

    Would it be possible to provide an image of the scope capture you've provided above, specifically C2, with greater resolution.  It appears as if the waveform is distorted or clipped around the same time as the A/B pulses are modulated.  Does the velocity measurement sampled from the interface show a different behavior?

    Sean

  • Hello Sean

    The picture as below. We also use SPI interface read VELOCITY REGISTER from AD2S1210, It’s very accurate about velocity.

    But Encoder interface has about 10% error. Could you help suggestion to solve this issue? Thank you. 

    BR

    Patrick

  • +1
    •  Analog Employees 
    on Nov 30, 2020 7:33 PM 2 months ago in reply to patrickchen@morrihan.com

    Patrick,

    Can you confirm what the settings for the encoder interface so that I can do some math to see if we aren't running into what I would characterize as a quantization error related to the master clock?

    To confirm lets take a case where we see the issue, like at 60000 RPM.

    Can you please confirm your use conditions,  from what I recall.

    • Resolution (POSITION/VELOCITY REGISTERS): 12-Bit
    • Master Clock:  10.24 MHZ
    • When we state 60000 RPM we mean electrical revolutions, i.e. the input to the RDC, not the rotation rate of the mechanical system.

    Thanks 


    Sean

  • Hello Sean

              Yes. The condition above is correct. But RPM is 64000 RPM.  We check with customer and they modify encoder resolution from 12bit to 10 bit and they get better signal quality that has less variation. But if run 64000 RPM, customer will read 16000 RPM for 1/4 time RPM via encoder interface. Do you have any comments for it?

                Do we have any encoder resolution versus Max RPM (RDC input) relationship formula or doc.?  Thank you. 

    BR

    Patrick

  • +1
    •  Analog Employees 
    on Dec 1, 2020 6:30 PM 2 months ago in reply to patrickchen@morrihan.com
    But if run 64000 RPM, customer will read 16000 RPM for 1/4 time RPM via encoder interface. Do you have any comments for it?

    By reducing the resolution to 10-bits the effective weight of each pulse transition( angular position change per edge)  increases by a factor of 4.  Thus for a given unit of time the number of pulses measured *4 should be equal to the same measurement range observed at 12-bit resolution.   Thus the customers reading of 16000 RPM in 10-bit mode is in fact still 64000 RPM.   

          Do we have any encoder resolution versus Max RPM (RDC input) relationship formula or doc.?  Thank you. 

    BR

    The incremental encoder is a function of position in that we observe a single edge transition (on either A or B) for every 360/2^RES degrees; for short we'll refer to the distance between sequential pulse transitions as R, for the rotational displacement.  Thus the pulse width of either A or B should be equal to 2*R/time and would be representative of the angular rotation velocity.  Note that the digital is limited to change at a rate that is a function of the master clock, thus the time resolution is 1/MCLKIN which will be in the range of 122ns.  Thus depending on the rate of rotation an error in the pulse width of up to about 66ns could be observed in the velocity.

    So utilizing 64000 RPM and 10.24MHZ (48.8ns)

    64000 RPM ~= 1066 RPS = 272,896 pulses per second (at 10-bits) which should be approximately 1.8us pulse width.  Thus with a time resolution error of 48.8ns would be about 2.7% maximum.  It then makes sense that at 12-bit the same error would result in about 10% (4*2.7 = 10.1%) as the period of the pulses at 12 bits would be 1/4 that of 10-bits.

    So in the end my suspicion of the "quantization" effect of the master clock at high frequency in the end was in fact accurate.