3
THEORY OF OPERATION
The secondary voltages are demodulated in the amplifier to
power a bridge network. A 3 Hz triangular wave is summed
with the error signal, defined by the difference between the
voltages, to effect the time proportioning. (See Figure 2.)
The sum is compared to a reference voltage by two Schmitt
triggers, which drive the solenoids. As the slope sensor
rotates, the triangular wave moves up or down with respect
to zero error signal. When the triangle crosses the upper or
lower trigger level the output signal is turned on. When a
Remote Setpoint is used, the difference between the volt-
ages is kept proportional to the commanded slope. The
separation between the reference voltages (the deadband)
is adjustable through a trim potentiometer in the front panel.
At minimum sensitivity (maximum deadband), a 0.4% slope
error signal will fire the triggers. At maximum sensitivity
(minimum deadband), both triggers will fire alternately at the
peaks of the triangular waves, even when the system is level.
The sensitivity adjustment controls the difference between
the upper and lower trigger from overlap to 0.5% slope.
The MCW100C,E Time Proportional Grade Controller con-
sists of a grade-sensing transducer and an amplifier. The
sensor and amplifier are housed in a single aluminum chan-
nel and can be removed easily for repair or replacement.
They are connected with a MS-connector.
Steering and grade information is sent to the Controller
through either a right angle or straight tube follower. Right
angle followers are used to sense grade and are either
tubular (for stringlines) or skate and ski (for firm reference
surfaces). Straight followers are used to sense a steering
path and are tubular. As the reference is raised or lowered -
left or right for steering - the transducer shaft is rotated so that
the follower maintains contact.
The transducer transforms this shaft rotation into an electrical
signal through the rotor/stator interaction. (See Figure 1.)
A 440 Hz square wave from the amplifier is applied to the
primaries of coils A and B. The stator position with respect to
the rotor determines the voltages from the coil secondaries.
Figure 1.
1814
1815
Figure 2.
0
error
t
0
output signal to the solenoid valve
min. sensitivity
t
upper trigger level
0
no output signal to the solenoid valve
max. sensitivity
max. sensitivity
min. sensitivity
lower trigger level
adjust
sensitivity
upper trigger level
BLN-95-9013