Update Rates; Hard Speed Reference Update Rate; Sources And Destinations - Emerson unidrive sp User Manual

Parameter Keypad and
Parameter x.00
structure display
4.2.3

Sources and destinations

1. Bit and non-bit parameters may be connected to each other as
sources or destinations. The scaling is as described previously.
2. All new source and destination routing only changes to new set-up
locations when the drive is reset.
3. When a destination pointer parameter within the drive or a dumb
Solutions Module (SM-Resolver, SM-Encoder Plus, SM-Encoder
Output Plus, SM-I/O plus) is changed the old destination is written to
zero, unless the destination change is the result of loading defaults
or transferring parameters from a SMARTCARD. When defaults are
loaded the old destination is set to its default value. When
parameters are loaded from a SMARTCARD the old destination
retains its old value unless a SMARTCARD value is written to it.
4.3

Update rates

Update rates are given for every parameter in the header table as shown
below.
3.03 Speed error
Drive modes Closed-loop vector, Servo
Bit SP
Coding
Range Closed-loop vector, Servo
Update rate 4ms write
Some parameters have an increased update in special circumstances.
4.3.1 Speed reference update rate
The normal update rate for the speed references (via menu 1) is 4ms,
however it is possible to reduce the sample time to 250μs by selecting
the reference from particular sources. The fast update rate is only
possible provided the conditions given below are met. (Note: high speed
updating is not provided for frequency references - i.e. Open-loop
mode).
Analog input references (not including I/O expansion Solutions
Module)
1. The reference must be derived via Pr 1.36 or Pr 1.37
2. The analog inputs must be in voltage mode with zero offset
3. Bipolar mode must be used or unipolar mode with the minimum
speed (Pr 1.07) set to zero
4. No skip bands are enabled, i.e. Pr 1.29, Pr 1.31 and Pr 1.33 must be
zero.
5. The jog and velocity feed-forward references must not be enabled.
Applications and fieldbus Solutions Modules
Pr 91.02 must be used to define the speed reference (this parameter is
only visible from the Solutions Modules). Any value written to Pr 91.02
should be automatically mapped into preset Pr 1.21 by the Solutions
Module.
In fast update mode the references are sampled every 250μs. A sliding
window filter may be applied to analog input 1 (see Pr 7.26) in normal or
high speed updating modes. The default value for this filter is 4ms,
therefore Pr 7.26 must be set to zero to obtain the fastest possible
update rate.
When fast updating is used the scaling is performed by a simple
multiplication. This minimizes software execution time, but also ensures
that there is no loss of resolution from the v to f converter used to
implement analog input 1. Therefore the speed of the motor may be
controlled with infinite resolution from analog input 1 except for
deadband effects around zero reference. The scale factor used for the
multiplication cannot exactly duplicate the scaling for the two stage
conversion (i.e. conversion in menu 7 to a percentage of full scale, and
conversion to 0.1rpm units) used when high speed updating is not in
operation. Therefore the absolute scaling of the analog inputs varies
slightly between normal and high speed updating.
24
Parameter Advanced parameter
description format
FI DE Txt VM DP ND RA NC NV
1 1 1 1
±SPEED_MAX rpm
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Serial comms
Macros
descriptions
PT US RW BU
1 1
The amount of difference depends on the maximum speed, user scaling
in menu 7, and the analog input 1 the filter time.
The worst case difference for analog input 1 is 0.12% of full scale, and
for analog inputs 2 and 3 the difference is less than 0.12% with a
maximum speed of 50rpm or more. Typical differences (1500rpm
maximum speed, menu 7 scaling of 1.000, analog input 1 filter of 4ms)
are 0.015% for analog input 1 and 0.004% for analog inputs 2 and 3.
4.3.2

Hard speed reference update rate

The normal update rate for the hard speed reference is 4ms, however it
is possible to reduce the sample time to 250μs by selecting the
reference from particular sources. The fast update rate is only possible
provided the conditions given below are met.
Analog inputs (not including I/O expansion Solutions Module)
The analog inputs must be in voltage mode with zero offset
Limitations are the same as for the references via menu 1 described
above.
Applications and fieldbus Solutions Modules
For faster update rate Pr 91.03 must be used (this parameter is only
visible from the Solutions Modules). Any value written to Pr 91.03 is
automatically mapped into the hard speed reference Pr 3.22.
Encoder reference
It is possible to use the drive encoder as the source for the hard speed
reference. To do this the drive encoder reference destination (Pr 3.46)
should be routed to the hard speed reference parameter. If, and only if,
the maximum drive encoder reference (Pr 3.43) is set to the same value
as the maximum reference value (SPEED_FREQ_MAX), and the
scaling (Pr 3.44) is 1.000, the drive takes the encoder pulses directly.
This gives a form of reference slaving where the integral term in the
speed controller accumulates all pulses from the reference and tries to
match them to the feedback from the motor encoder. Pulses are lost if
the reference reaches a minimum or maximum limit including zero speed
in unipolar mode. The reference is sampled every 250μs. It is possible to
apply scaling even in this high speed update mode by changing the
number of encoder lines per revolution. It is also possible to use this high
speed update mode with some position feedback category Solutions
Modules (see description for the appropriate Solutions Module).
Electronic
Performance
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PS
Unidrive SP Advanced User Guide
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Issue Number: 10