ATU-HP Technical Instruction Manual
Page 6-9
Section 6 Theory of Operation
Issue 2.0
6.3.7 Serial Communications
(RS485)
Microcontroller U8, ICs U12 through U15
and their associated components form the
serial communications circuit. U12 and U13
are opto-isolators used to provide isolation
between the ATU-HP and the associated
transmitter. U14 translates the TTL outputs
from U12 and U13 to balanced RS485. U15
(isolated dc-dc converter) supplies power to
the isolated circuit.
6.3.8 Motor Limit Control
See Figure SD-1. The motor limit control
circuitry consists of photo-interrupter
devices A4U1, A4U2 (for inductive tuning),
A2A1U1 and A2A1U2 (for resistive tuning)
and their associated components.
For inductive tuning, a mechanical travel
indicator, located on the inner coil shaft,
interrupts A4U1’s operation if the inner coil
is at its minimum inductance and interrupts
A4U2’s operation if the inner coil is at its
maximum inductance. For a minimum limit,
an open circuit will be present on J1-6 of the
limit switch PWB (A4). This removes the
ground normally applied to the ATU control/
monitor PWB’s
L Limit Min
input (A1J2-7).
For a maximum limit, an open circuit will be
present on J1-11 of the limit switch PWB
(A4). This removes the ground normally
applied to the ATU control/monitor PWB’s
L
Limit Max
input (A1J2-8).
For resistive tuning, a mechanical travel
indicator, located on the inner coil of the
resistive matcher, interrupts A2A1U1’s
operation if the resistive matcher is at
maximum and interrupts A2A1U2’s
operation if the resistive matcher is at
minimum. For a maximum limit, an open
circuit will be present on J1-13 of the
variable matching transformer assembly’s
limit switch PWB (A2A1). This removes the
ground normally applied to the ATU control/
monitor PWB’s
R Limit Max
input
(A1A1J2-5). For a minimum limit, an open
circuit will be present on J1-1 of the variable
matching transformer assembly’s limit
switch PWB (A2A1). This removes the
ground normally applied to the ATU control/
monitor PWB’s
R Limit Min
input (A1J2-6).
