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high resolution sincos encoder


spadin
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I want to use a high resolution sincos encoder with 1.6e6=2^21 lines and interpolation to 16,384=2^14 per line. That requires a dynamic range of 35 bits.

1. Does power PMAC have enough dynamic range in its servo calculations to support this?

2. What is the maximum input frequency for an ACC-24 or ACC-51 sincos input?

3. Is the maximum input frequency the same for a TTL quadrature encoder?

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spadin,

 

1. All Servo related data registers in Power PMAC are 64-bit double precision variables with 52-bit mantissa which would be sufficient for your encoder even if you decide to used the LSB of interpolation as a unit for motor unit scale. (Since we have double precision floating point, we would suggest setting the EncTable[n].ScaleFactor for Sinusoidal encoders on ACC-24E3 to 1/4096 so you would have equivalent of quadrature as output of encoder conversion table without losing any of the interpolation resolution by carrying it as decimal portion. This will result in Servo gains with higher magnitude, which might be easier to work with. Mathematically the scale factor is not important since eventually it will be cancelled out between the output of ECT, Motor[x].PosSf and Motor[x].Pos2Sf and Servo loop gains).

 

2. On ACC-24E3 and ACC-52E we can accept up to 8MHz line frequency for Sinusoidal encoder input option.

 

3. The maximum input frequency for TTL quadrature encoder input is much higher in ACC-24E3. In ACC-24E2x series the sampling clock can be as fast as 40MHz which allows a 32MHz quadrature input with a 20% safety margin. In ACC-24E3 series we can increase the sampling clock as fast as 100MHz, however neither the encoder nor input circuitry would be able to support that speed.

 

Regards,

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