ElmoMC SimplIQ Software Manual - Manual (Page 13)

SimplIQ Software Manual Communication with the Host
MAN-SIMSW (Ver. 1.4)
2-4
2.3.2 Speed and Acceleration
Speed is measured in counts/second and acceleration is measured in counts/second 2 .
The speed units may be related to physical units by converting the counts to revolutions,
meters or other, as explained in
section 2.3.1 .
2.3.3 Current and Torque
Currents are measured in amperes, although there is no single accepted method for
specifying the current of three-phased motors. For sinusoidal motors, RMS phase current
normally specifies the motor current. The RMS is determined during a mechanical
revolution so that phase currents are the “motor current” only if the motor revolves at a
constant speed. For trapezoidal motors, the conventional six-step drive leaves one motor
phase open-circuited, and only one current flows through the two driven motor phases.
This driven-phase current specifies the “motor current.” For trapezoidal motors running
six-step commutation continuously at 1 ampere, the RMS current is 0.92 amperes.
SimplIQ drives have a single motor current definition, although it can run equally well
with sinusoidal, trapezoidal or free-form motor windings. Motor current is defined as the
maximum winding current in a mechanical revolution. This definition is consistent with
the traditional current definition for six-step motors and it can be readily extended to
other winding forms.
To obtain the RMS phase current for sinusoidal motors, multiply the motor current
reported by the
SimplIQ drive by a factor of 0.71.
2.4 Internal Units of Measurement and Conversion
In order to optimize the use of its CPU, the SimplIQ drive operates internally with local
units for time, current, DC bus voltage and electrical angle.
ƒ
While time is normally measured in seconds, most control algorithms measure time
by counting controller sampling times.
ƒ While current is usually measured in amperes, the SimplIQ drive performs this
measurement internally in terms of A/D bits.
ƒ Rather than degrees or radians, the SimplIQ drive divides the electrical cycle into 1024
sections.
These internal measurements are normally transparent to the user, because the SimplIQ
drive translates its internal calculations into standard units of measurements. However,
the following situations require the user to use the internal data representation:
ƒ
Uploading data from the real-time recorder
ƒ Interpreting CAN-mapped synchronous PDOs
ƒ Specifying motions in micro-stepping mode
In these situations, the conversion factors can be retrieved using the relevant user
interface commands.