Accel And Decel; Maximum Speed - PowerTec 2000C Instruction Manual

JUMPER EFFECT OF PUTTING JUMPER IN
POSITIONN THE INDICATED POSITION
ACCEL and DECEL rates are
OUT
fixed at about 50mS from
zero speed to full speed.
ACCEL and DECEL rates are
IN
independently adjustable
by the ACCEL and DECEL
potentiometers from about
2 seconds to about 30
seconds.

5.1.3 ACCEL AND DECEL

The input reference command is held at zero inter-
nally while the control is off, and is releasedat the level
present at TB2 terminal 10 to the ACCEL/DECEL circuit
when the drive is started.
The ACCEL/DECEL circuit changes the reference
rate of increase from a step, or near-step function to a fixed
rate of increase or decrease which is adjustable by the
ACCEL and DECEL pots. The rate will be affected by the
Speed Controller board jumper labeled JP2. When jumper
JP2 is installed, the control is in the RATE LIMITED
mode. When jumper JP2 is NOT installed, the control is in
the DIRECT mode.
In the RATE LIMITED mode, the ACCEL and
DECEL pots may be used to set a desired rate of change of
speed between 2 seconds and 30 seconds in standard units.
If the desired ACCEL rate does not cause the motor to go
to current limit, the change in speed will happen at a linear
rate. If the required ACCEL rate is too fast for the available
torque and load, the control will reach current limit, and
that will modify the rate of change of speed.
Since the Models 2000C and 3000C are not regen-
erative, the DECEL rate will only be effective if the coast
time of the motor and load is shorter than the desired
DECEL rate (see section 1.2 for explanation of the terms).
The ACCEL and DECEL adjustments have very
little effect in the DIRECT mode. This mode is used when
speed changes must be very fast, such as with a rapidly
changing input reference signal. However, be aware that
speed changes in the DIRECT mode will be in CURRENT
LIMIT (for increasing speeds) or by coasting (for decreas-
ing speeds). When the 2000C or 3000C is in current limit,
the rate of change of motor speed is limited by the drive's
current limit, not by a change in the signal. The drive
cannot track large changes in the speed signal which
approach step functions.
The ACCEL and DECEL potentiometers have no
effect when the control is operated in the DIGITAL mode
since the 2000C or 3000C is operating without using the
VCO and the analog ciruits are disconnected.
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Page

5.1.4 MAXIMUM SPEED

The analog circuits process the analog input signal
for such functions as ACCEL and DECEL ramps, and
JOG. The output of the analog reference circuits must then
be converted to a frequency so the digital circuitry of the
Model 2000C may take over. This conversion is accom-
plished by a Voltage Controlled Oscillator (VCO), whose
output in hertz is directly related to the voltage level at its
input. The VCO is an infinitely variable circuit (as opposed
to a circuit which operates in 512, 1024, or 2048 steps).
The output frequency of the VCO must be calibrated
to the input voltage of the VCO. This is usually set at the
10VDC input level, but it may be done at other levels.
POWERTEC Brushless DC motors come with en-
coders which will produce a feedback rate of either 120
(four pole motors) or 240 (eight pole motors - 280 frames
and larger) pulses-per-revolution of the motor shaft. This
requires that the VCO produce a frequency which is equal
(in hertz) to two times or four times the RPM of the motor.
For a 1750 RPM four pole motor, this works out to 3500
hertz (120 pules/ revolution X 1750 revolutions/ minute X
1/60 minutes/ second = 3500 pulses/ second (hertz). For an
eight pole motor, the pulse rate is 7000 Hertz for the same
speed.
The calibration (maximum speed) adjustment for
the applied analog reference may be accomplished with a
handheld tachometer. During start-up, when the time
comes to set the maximum speed (preferably after the
motor has reached operating temperature), the calibration
is made by adjusting the MAX SPD potentiometer for the
nameplate RPM rating while the speed pot is set for
+10VDC at TB2 terminal 10, measured with respect to
TB2 terminal 12. The MAX SPD pot is adjustable from
about 2000 to about 10000 hertz (with a +10VDC input
reference). This corresponds to about 1000 to 5000 RPM
on the standard two pole motor and about 500 to 2500 RPM
on the standard eight pole motor. (Eight pole Brushless DC
motors are generally those with frames 280 or larger.).
If the MAX SPD pot is set too low, the motor will not
run up to its rated speed, although it will continue to
increase its speed over the entire range of the operator
speed pot adjustment from 0% to 100%. If this is the case,
then the MAX SPD pot may be turned clockwise until the
motor is running at rated speed.
NOTE: If the motor is cold, and is heavily loaded, the
motor may not come all the way up to rated speed. This will
be indicated by the CURRENT LIMIT light coming on,
though there is no appreciable amount of load and large
amounts of current are not being drawn. The motor is not
running up to rated speed, although the MAX SPD pot is
turned beyond the point where speed has stopped increas-
ing. If this happens, allow the motor to run for a while
before making the MAX SPD setting.
Model 2000C / 3000C Manual