58
To obtain good performance at low speed it is necessary to select an encoder resolution for the
master that sufficiently high.
More precisely, the signal coming from the encoder can be adapted according to the report
P221/P222 and, if necessary, one of the analog input
3.1.3.3 FREQUENCY SPEED REFERENCE MANAGEMENT
The speed reference in pulses is very accurate (no pulses is lost) but for its nature it has an irregular
shape because are counted the edges every sampling period (TPWM) and this produce a speed
reference with many noise. Also if the frequency input is constant, between a PWM period and
another could be counted a variable number of pulses,
± one pulse. This produce a low resolution
reference, expecially when the frequency input decreases.
For not use a big filter with frequency reference it’s possible to use its time decode that has a good
resolution. It is measured the time between various edges of frequency input with resolution of 25ns,
reaching a percentage resolution not less than 1/8000 (13 bit) working to 5KHz of PWM (increasing
PWM resolution decreases linearly).
There are 3 different ways to manage frequency speed reference, selectable with parameter
P224 (FRQ_REF_SEL):
P224 Description
0
Pulses reference
1
Decoded in time reference
2
Pulses and decoded in time reference
Enabling the frequency speed reference can be done by the parameter P223 = 1 (EN_FRQ_REF) or
bringing at active logic state input function I19.
Master Slave
N° of pulses/revolution = 512 N° of pulses/revolution = 512
P65 = 2500 rpm P65 = 2500 rpm
P221 = 50 P222 = 100
The slave goes at the half speed as the master
Master Slave
N° of pulses/revolution = 512 N° of pulses/revolution = 512
P65 = 2500 rpm P65 = 2500 rpm
P221 = 100 P222 = 50
The slave goes at the double speed as the master
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