PowerTec Regenerative Brushless DC Motor Control 1000AR - Manual (Page 29)

Page
28
Model 1000AR Installation and Operation Manual
6/4/2001 © copyright 1997 by Powertec
ANALO G VERSUS DI G I TAL O PERATI O N
The choice between ANALOG and DIGITAL operation comes down to performance.
In ANALOG mode, a voltage sets the speed of the motor. Due to analog component tolerances, the
best accuracy you can expect is on the order of +/- 1%. It is typically 0.1% or better. The biggest problem
with Brushless DC is not the following of an analog source. It is the obtaining of a clean and stable analog
source to follow. Electrical noise can
be a nasty problem, and you must
use good shielding methods.
In single motor operation, the
motor does not have to follow a
precise speed or a profile generated
by another motor or other source.
The ANALOG speed reference is
adequate in almost all cases. Changing load does not change the speed of the motor.
Coordinating the speed of two or more motors with analog methods requires some type of trimming
device, such as a dancer or load cell. Analog tolerances and noise make exact coordination very hard.
In DIGITAL mode, the speed of the motor is proportional to the frequency of the pulse train presented
at the TB1 terminals 11 and 9. Each pulse to the drive at these terminals will require a pulse from the
motor. The EEPROM multiplier used
in the Current Controller board
determines the effect of the pulse
from the motor. Analog tolerances do
not disturb the system, nor will there
be any temperature drift.
For single motor operation, use
DIGITAL methods where precise
speeds are important, that is, if you
really want to be able to set 1749 RPM and get that speed precisely. Motor load does not change the
speed and the speed set by DIGITAL means has a drift of 1 Speed Reference pulse (less than 3° of motor
shaft rotation).
Speed coordination of two or more motors requires DIGITAL means for systems that do not have a
trimming device. Two motors connected by DIGITAL signals will track pulse for pulse.
Even though the motors may be made to operate together or in an exact ratio, there is a possibility
that the mechanical system or the speed setting devices may not be identical. If this is the case, some
type of trimming device may be necessary in a digital system. If the material does not stretch, this will
become apparent in short order.
ANALOG Value
Speed Regulation 0% from No Load to Full Load
Speed Accuracy +/- 1% of Speed Reference
Speed Drift +/- 1% of Speed Reference
DIGITAL Value
Speed Regulation 0% from No Load to Full Load
Speed Accuracy 1 Motor Feedback Pulse for each Pulse
of Speed Reference
Speed Drift +/- 1 Speed Reference Pulse