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Unidrive SP Advanced User Guide 63
Issue Number: 7 www.controltechniques.com
When Ab, Fd, Fr, AbServo, Fd.Servo, Fr.Servo, SC, SC.Hiper, SC.EnDat or SC.SSI encoder are used the equivalent number of encoder lines per
revolution must be set-up correctly in Pr 3.34 to give the correct speed and position feedback. This is particularly important if the encoder is selected
for speed feedback with Pr 3.26. The equivalent number of encoder lines per revolution (ELPR) is defined as follows.
For any type of linear encoder one revolution is the motor pole pitch multiplied by the number of poles set up in Pr 5.11 or Pr 21.11.
Ab.Servo, Fd.Servo, Fr.Servo
The incremental (A/B) signal frequency should not exceed 500kHz.
SC.Hiper, SC.EnDat, SC, SC.SSI
The sine wave signal frequency can be up to 500kHz, but the resolution is reduced at higher frequencies. The table below shows the number of bits
of interpolated information at different frequencies and with different voltage levels at the drive encoder port. The total resolution in bits per revolution
is the ELPR plus the number of bits of interpolated information. Although it is possible to obtain 11 bits of interpolation information, the nominal design
value is 10 bits.
If the position feedback device is a rotary SINCOS encoder with comms the position supplied via comms gives a number of counts per revolution that
is a power of two and the resolution is defined by the single turns comms bit (Pr 3.35). It is assumed therefore that the number of periods per
revolution is also a power of two, and so if a SC.Hiper, SC.EnDat or SC.SSI type devices is selected and Pr 3.39 is 1 or 2 to select a rotary encoder =
1 or 2, Pr 3.34 is forced to be a power of two between 2 and 32768.
When Pr 3.34 is adjusted an Enc7 trip is produced, because the encoder requires re-initialisation. If this parameter is set to a value that is not a power
of two and the encoder is set up as a linear encoder (Pr 3.39 = 0) the sample rate for the current controllers is reduced to 6kHz for 6 or 12kHz
switching frequency. All other switching frequencies are unaffected. See Pr 5.37 on page 121.
If the position feedback device is SC.Hiper or SC.EnDat it is possible for the drive to set up this parameter automatically from information obtained
from the encoder (see Pr 3.41 on page 69).
EnDat, SSI
Where encoder comms alone is used as position feedback, the equivalent lines per revolution (Pr 3.34) is not used in setting up the encoder interface.
It is possible for the drive to set up this parameter automatically from information obtained from an EnDat encoder (see Pr 3.41 on page 69).
Linear motors
The value entered in this parameter for a linear motor should be calculated as follows:
If this value is not an integer then an SM-Universal Encoder Plus is required.
Ab, Fd, Fr, Ab.Servo, Fd.Servo, Fr.Servo, SC
Pr 3.35 has no effect.
SC.Hiper, SC.EnDat, SC.SSI and 03.39 = 1 or 2 (Rotary encoder)
Pr 3.35 must be set to the number of comms bits used to represent one revolution of the encoder. The single turn comms resolution may be higher
than the resolution of the sine waves per revolution.
SC.Hiper, SC.EnDat, SC.SSI and 03.39 = 0 (Linear encoder)
Pr 3.35 must be set up to the total number of bits representing the whole encoder position in the comms message. This parameter is not used with
linear SC.Hiper encoders as the number of bits used to represent the whole position is always 32.
EnDat, SSI
Pr 3.35 must be set to the number of bits used to represent one revolution of the encoder.
Although Pr 3.35 can be set to any value from 0 to 32, if the value is less than 1, the resolution is 1 bit. Some SSI encoders (SC.SSI or SSI) include a
power supply monitor alarm using the least significant bit of the position. It is possible for the drive to monitor this bit and produce an Enc6 trip if the
Position feedback device ELPR
Ab, Ab.Servo number of lines per revolution
Fd, Fr, Fd.Servo, Fr.Servo number of lines per revolution / 2
SC.Hiper, SC.EnDat, SC, SC.SSI number of sine wave periods per revolution
Volt/Freq 1kHz 5kHz 50kHz 100kHz 200kHz 500kHz
1.2 11 11 10 10 9 8
1.0 11 11 10 9 9 7
0.8 10 10 10 9 8 7
0.6 10 10 9 9 8 7
0.4999876
3.35
Drive encoder single turn comms bits / Linear encoder comms bits
Drive modes Open-loop, Closed-loop vector, Servo
Coding
Bit SP FI DE Txt VM DP ND RA NC NV PT US RW BU PS
111
Range Open-loop, Closed-loop vector, Servo 0 to 32 bits
Default Open-loop, Closed-loop vector, Servo 0
Update rate Background read (Only has any effect when the drive is disabled)
Pr 3.34 PPR setting
Motor pole pitch
Encoder pitch 4×()
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