Basis Weight Actuator
17
Figure 13. Valve Position Indicator Block Diagram
(PANEL ADJUST.)
VOLTAGE
AMP
(0–1 V)
(PANEL
ADJUST.)
(FACTORY
ADJUST.)
(FACTORY
ADJUST.)
CURRENT
DRIVER
INPUT TO
POSITION
INDICATOR
E0019 / IL
both modes, and is governed by the torque dropping
off enough that the motor stalls.
The stroking time is controlled by the frequency of the
internal oscillator. The oscillator triggers the stepper
motor drive card to provide properly phased currents
to the various windings of the stepper motor. The se-
quence of energization of the windings is designed to
move the rotor one motor step per oscillator pulse. In
this stepping mode, 400 positions are available per
motor revolution. The gear ratio of the specific actuator
then determines how many motor revolutions are re-
quired to produce 90 degrees of output shaft rotation,
providing the multiplier to determine the resolution of
the valve travel.
The shortest contact closure to which the IC2000/SKF
will respond depends on the setting of the computer
mode speed potentiometer and the time skew between
the user’s gating signal and the IC2000’s internal oscil-
lator.
The output of the oscillator is an asymmetric pulse sig-
nal which is low for about 25 microseconds of the peri-
od. The stepper motor is guaranteed to move one step
if the signal to the driver card has been low for at least
10 microseconds prior to going high again. However,
there is no way to synchronize the DCS contact clo-
sures with the internal oscillator. So, the external con-
tacts must be held closed for 10 microseconds longer
than the period of the oscillator to guarantee at least
one step movement of the motor. On occasion, this
length of contact closure will result in 2 steps move-
ment (specifically when the contact closure happens to
occur simultaneously with the beginning of the oscilla-
tor low phase).
Therefore, if you had an oscillator set up for 10.1 steps
per second (99msec/step) and sent an Increment com-
mand that lasted 200 milliseconds, you would move
the valve 2 steps in the open direction.
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