Emerson FM-3 - Manual (Page 54)

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FM-3 Programming Module Reference Manual
If the user decides to put a 5:1 reducer on the system, the user simply needs to change the
Characteristic Length.
Now the belt travels 4.71" in 5 motor revolutions.
Keep in mind that the characteristic length is always a whole number and the valid range is
from 1 to 2000.
Note
User Units may affect end motor speed and could cause trajectory faults.
Because of internal math in the FM-3 and FM-4, some user unit combinations may cause
module or drive trajectory faults. The maximum motor velocity allowed by the drive is
detailed under the distance section of the User Units View and is labeled “User Unit Limited
Speed”. When the user unit setup is altered in such a way that the maximum motor speed
allowed by the drive is less than the maximum speed allowed by the chosen motor, the readout
of maximum motor speed allowed by the drive changes to have a red background. If a
configuration is downloaded to the FM-3/4 with a red background on the “User Unit Limited
Speed”, the drive will obtain a trajectory fault at speeds near this velocity. To alleviate this
issue, simply remove decimal places from your user units, and/or change the characteristic
distance (numerator) of your scaling parameters to be a smaller number that it was. The red
background indicating module trajectory faults will go away when the user unit setup is
scaled for a realistic accuracy based on the encoder counts per revolution.
Velocity Group
Enable Separate Distance Units Check Box
If checked, separate distance and velocity units, name and scaling will be enabled. If not
enabled, the velocity units, name and scaling will be defined by the Distance Group.
Scaled Distance Name
If the user wants the velocity units to have a different distance scaling than the distance units
a name can be entered here up to 10 characters. For example, the user distance units could be
inches while the velocity units are feet per minute.
Velocity Distance Units Scale Factor
This parameter scales the Velocity Distance Units back to actual distance units. To do this,
enter the number of distance user units that are equal to one velocity scaled distance unit.
Scaling
Characteristic Distance = 4.712
Characteristic Length = 5
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