
SM-Universal Encoder Plus User Guide
89
Issue Number: 6
www.controltechniques.com
The position feedback can be used as a reference for any unprotected parameter and is
the output from the speed filter (Pr
x.19
). This value is also displayed in Pr
x.03
after
further filtering to aid readability.
The filtered reference is converted to percentage of the maximum position feedback
reference (Pr
x.20
) and displayed via the feedback reference (Pr
x.21
). This value is to
the nearest tenth of a percent and is limited to
±
100.0%. The limited percentage value
is then scaled by the feedback reference scaling (Pr
x.22
). This scaled value is also to
the nearest tenth of a percent and is also limited to
±
100.0%. The value written to the
destination parameter is converted to a percentage of the full-scale value of the
destination (Pr
x.23
) to the nearest tenth of a percent.
The destination is updated every 4ms.
If the destination for the feedback is the hard speed reference (Pr
3.22
), a shortcut
facility is provided in the drive. In order to invoke this facility, the maximum feedback
reference (Pr
x.20
) must be set to the maximum currently used for the hard speed
reference and the scaling parameter (Pr
x.22
) must be set to 1.0000. The destination is
updated every 250
µ
s and a value in rpm is written to Pr
3.22
every 4ms for indication
only.
Example
Speed is 200rpm Pr
x.20
is 400rpm so Pr
x.21
shows 50%. Pr
x.22
is 0.500 so the final
percentage value is 25%. The destination is a 16 bit bipolar parameter which therefore
will have 25% * (2^15) = 8192 written to it.
Effect of encoder resolution
A 1024 line encoder as the input produces 4096 counts per revolution. The resolution is
one count per 250
µ
s. As one count is 1/4096th of a revolution, the speed resolution is
actually 58.8rpm.
A 4096 line encoder as the input produces 16384 counts per revolution. As one count is
1/16384th of a revolution, the speed resolution is actually 14.6rpm.
To compensate for the resolution of one count per 250
µ
s the speed filter can be used.
For example a filter of 4ms divides the resolution by 16, but could affect the
performance of any control loop.
Effect of percentage resolution
Destinations other than the hard speed reference (Pr
3.22
) will be rounded to the
nearest tenth of a percent. This would give a minimum resolution of 1 rpm if the
destination maximum were 1000.0rpm for example.
If the destination is default or invalid (non-existent or protected) Pr
x.21
displays the
motor thermistor resistance in 0.1% of 10k
Ω
units. This operates even if Pr
x.12
(thermistor enable) is not enabled allowing the user to design their own characteristic
without trips using the threshold detector.
NOTE
x.24
Encoder simulation source
RW
Uni
PT
US
Ú
00.00 to 21.51
Ö
00.00
Update rate: Read on reset
Содержание SM-Universal Encoder Plus
Страница 73: ...SM Universal Encoder Plus User Guide 73 Issue Number 6 www controltechniques com ...
Страница 112: ...0471 0005 06 ...