ElmoMC SimplIQ Command Reference - Manual (Page 58)

EF[N] - Encoder Filter Frequency
Purpose:
Filters encoder signal in order to improve its noise immunity. Because the logic of the
quadrature decoder must sense transitions, the inputs are first run through a glitch filter.
This filter has a digital delay line that samples four time points on the signal and verifies
that a majority of the samples are at a new state before outputting the new state to the
internal logic. The sample rate of this delay line is programmable, to adapt to a variety of
signal bandwidths.
When an analog encoder is used, the basic signal, before interpolation, is filtered using
the same method.
EF[N] sets the sample rate of the corresponding digital glitch filter: EF[1] for the main
encoder and EF[2] for the auxiliary encoder. A counter increases or decreases to the value
of EF[N]. When the count reaches the specified value, the counter is reset and the filter
takes a new sample of the raw A, B, Index and Home input signals. If EF[N] is zero the
digital filter is bypassed.
If EF[N] is large, the encoder reading noise immunity will be better, but true fast
transitions (occurring by fast speed) may be dismissed as false. A number that is too
small may cause the counting of noise pulses.
A good value for the required delay of the encoder filter is ¼ of the minimum time
expected between transitions.
Example:
Suppose that the maximum speed of a motor is 10,000 rpm and that the motor is
equipped with an encoder with 1000 lines (4000 counts/rev with resolution
multiplication). The expected minimum encoder transition time is:
60 sec/min
4000 cpr * 10,000 rpm
The encoder pulse time is calculated as sec 375
4
sec 5 . 1
n
=
μ
: Because of the CPU clock
frequency, the minimum required encoder signal stable time should be set to 400 nsec
(i.e. EF[ ] = 3)
The minimum required encoder signal stable time should be set to about:
1.5 μsec
4
The ranges of encoder frequency filtering are as follows:
EF[1] / EF[2] 0 1 2 . . . K 127
Filter time 25 nsec 200 nsec 300 nsec . . . 100*(K+1) nsec 12.8 µsec
When the interpolator is used, the time difference between consecutive signal
changes may be shorter. This is dictated by the interpolator’s specifications and not
from the motor speed.
= 1.5 μsec
≈ 375 nsec
SimplIQ Command Reference Manual Alphabetical Listing
MAN-SIMCR (Ver. 4.5)
3-45