SOMETHING TO CHECK: Find out what RPM your motors are actually running. If these are DC gearmotors, then most likely the motor is running much faster than the motor gear-reduced output speed. The PLC probably needs to use the actual motor speed range (not the geared output range). The only exception would be if the DC Drives are programmed to take the gear-reduction ratio into account on their speed input range. You can compute the actual motor speed range if you find the gear-reduction ratio (assuming that these are gearmotors).
Question for you again: How is the speed of the drives controlled right now, before your PLC ramp progtram is installed?
Question for you again: How is the speed of the drives controlled right now, before your PLC ramp progtram is installed?