Digital Reference - PowerTec 2000C Instruction Manual

Of course, in the analog speed mode, any 0 to
+10VDC reference signal will act as a speed command as
long as it is referenced to TB2 terminal 12, and the
direction of rotation will depend upon the polarity of the
voltage at TB2 terminal 14 with respect to TB2 terminal 12
in the analog speed mode.
Input voltages greater than +10.6VDC or -0.6VDC
are clamped by the input circuits. Nominal input imped-
ance for voltages less than +10VDC is 50Kohms. Potenti-
ometers used for speed pots should be no less than 2 Kohm
(reference supply limitation, and not greater than 10K.
Above 10 Kohms the pot is non-linear, so a setting of 50%
may give a speed of 47%. This is especially true with multi-
turn potentiometers, when non-linearity is made most
noticeable by the dial reading.
When a manual speed potentiometer which is sup-
plied by TB2 terminal 9 is used, the speed accuracy (versus
reference) of the control will be dependent on the stability
of the reference source and temperature and noise effects.
This is generally better than 1% after the drive and motor
have reached their operating temperatures.
If an external reference source is used, the control
will track the input voltage at TB2 terminal 10 within +/-
0.5%. The tolerances of analog circuitry determine how
well the control will do with an analog reference. While the
above numbers represent the worst cases, typical speed
accuracy performance in a load and temperature stabilized
system can be expected to be better than 0.1% of setpoint.
In analog mode of operation, maximum motor speed
in relation to the applied reference is determined by
adjustment of the MAX SPEED potentiometer on the
Speed Controller. This pot calibrates the motor speed for
the applied reference. The Brushless DC motor, by itself,
will not exceed its base speed by very much when it is
heavily loaded. It is possible that, if the MAX SPEED pot
is turned up too far, and the load is light, it will seem to have
no effect. The maximum speed of the motor will not be
attained until the motor has reached operating tempera-
ture. Like any NEMA standard DC motor, a warm-up time
is necessary to reach operating temperature, due to the fact
that a cold motor develops more CEMF (and therefore
more torque). The MAX SPEED adjustment has no effect
in digital mode.
The onboard JOG pot is analog. It is activated by the
JOG circuit, which overrides the RUN circuits. The onboard
JOG pot does not determine the JOG speed while the
Model 2000C control is operating in the DIGITAL MODE.
It is not necessary to reduce the input reference to
zero before starting or stopping the 2000C or 3000C. The
reference input circuits and the accel/decel circuits are
clamped while the control is stopped. The clamp is released
when the RUN is activated. The clamp is turned on also for
the RAMP STOP function. The speed pot may be left at its
speed setting, or an external reference may be left con-
nected while the control is decelerating during the RAMP
STOP function, or while the control is stopped. When
RUN is restored, the control accelerates at the accel rate.
© copyright 1992, 1996 by Powertec Industrial
Motors

4.52 DIGITAL REFERENCE

Since the Brushless DC motor control system is
inherently digital, the performance in the digital mode of
operation far exceeds the performance in the analog mode.
In the digital mode the control and motor respond to a
frequency signal which is fed to the control from an
external source In digital mode the same digital circuitry
is used for the speed control as is used in the analog mode.
The analog output of the accel/decel circuits drives a
voltage-controlled-oscillator (VCO), which in turn feeds
the digital circuitry. In digital mode the VCO is bypassed
and an external frequency is used to control speed.
The digital mode is activated by applying a nominal
+24VDC voltage to TB1 terminal 10, positive with respect
to TB1 terminal 9 (Figure 16). There is also a jumper next
to P2 on the Current Controller board (Part # 4001-
141108) which, when placed in the AF position, switches
the control to digital mode without energizing terminal 10.
Figure 16: Analog/digital switch and frequency input
circuits of the Models 2000C and 3000C.
Either of these actions disconnects the control's
internal VCO and looks for a frequency at TB1 terminal 11,
which must be positive with respect to TB1 terminal 9. This
frequency signal must meet certain specifications:
"ON" VOLTAGE:
"OFF" VOLTAGE:
FREQUENCY:
DUTY CYCLE:
MAXIMUM FREQ:
The best tracking is gained by ramping the fre-
quency, changing the frequency gradually. If a frequency
is present when the control is turned on, the motor acceler-
ates in current limit. The nature of the Brushless DC motor
control is that the motor must return a pulse for each
reference pulse supplied, except in current limit! If the
control goes into current limit, pulses will be lost. So it is
best to not change the external frequency so rapidly that the
motor cannot respond without going into current limit.
18VDC min, 30VDC max
less than 1.5VDC
2X desired RPM
(250 frames or smaller)
25% min, 75% max
50 KiloHertz
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