Emerson Mentor MP Advanced User's Manual page 43

Parameter Keypad and
structure display
3.01 Final speed reference
Bit SP
Coding
Range ±SPEED_MAX rpm
Update rate 4ms write
This is the final speed demand at the input to the speed regulator formed by the sum of the ramp output and the hard speed reference (if the hard
speed reference is enabled). If the drive is disabled this parameter will show 0.0.
3.02 Speed feedback
Bit SP
Coding
Range ±SPEED_MAX rpm
Update rate 4ms write
The speed feedback can be taken from the drive encoder port or tachometer or armature voltage or a position feedback module fitted in any slot as
selected with Pr 3.26. Pr 3.02 shows the level of the speed feedback selected for the speed controller. Display filtering is active when this parameter
is viewed with one of the drive keypads. The value held in the drive parameter (accessible via comms or an option module) does not include this filter,
but is a value that is obtained over a sliding 16ms period to limit the ripple seen in this parameter value. The speed feedback value includes encoder
quantisation ripple given by the following equation:
Ripple in Pr 3.02 = 60 / 16ms / (ELPR x 4)
Where ELPR is the equivalent encoder lines per revolution as defined below:
Position feedback device
Ab
Fd, Fr
For example a 4096 line Ab type encoder gives a ripple level of 0.23rpm.
The 16ms sliding window filter is always applied to the value shown in Pr 3.02, but this sliding window filter is not normally applied to the
actual speed feedback used by the speed controller or the drive encoder reference system (Pr 3.43 to Pr 3.46). The user may apply a filter to
the speed controller input and the drive encoder reference system input if required by setting Pr 3.42 to the required filter time. The encoder ripple
seen by the speed controller is given by:
Encoder speed ripple = 60 / Filter time / (ELPR x 4)
If Pr 3.42 is set to zero (no filter) the ripple seen by the speed controller and drive encoder reference system is given by:
Encoder speed ripple = 60 / 250us / (ELPR x 4)
From the drive
encoder port
The diagram above shows the filter arrangement. It should be noted that the same filtering is provided at the speed controller input and for Pr 3.02
when the feedback is obtained from an option module, but the variable length window filter is controlled by Pr x.19.
It is not advisable to set the speed feedback filter too high unless it is specifically required for high inertia applications with high controller gains
because the filter has a non-linear transfer function. It is preferable to use the current demand filters (see Pr 4.12 or Pr 4.23) as these are linear first
order filters that provide filtering on noise generated from both the speed reference and the speed feedback. It should be noted that any filtering
included within the speed controller feedback loop, either on the speed feedback or the current demand, introduces a delay and limits the maximum
bandwidth of the controller for stable operation.
Mentor MP Advanced User Guide
Issue Number: 1
Parameter description
Parameter x.00
format
FI DE Txt VM DP ND RA NC NV
1 1 1 1
FI DE Txt VM DP ND RA NC NV
1 1 1 1
ELPR
number of lines per revolution
number of lines per revolution / 2
Filter
defined
by Pr 3.42
16ms
filter
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Advanced parameter Serial comms
descriptions protocol
PT US RW BU
1 1
PT US RW BU
1 1
Speed
controller
Drive encoder
reference
system
Pr 3.02 and
Pr 3.27
Performance
PS
PS
Menu 3
43