Figure 1-13.-A static logic panel for a cargo elevator.

connected in the line at start and are cut out in steps as

less space requirements. A typical static logic panel

the motor accelerates to the running speed.

found aboard ship is shown in figure 1-13.

Motors used with cargo winches and other deck

Although there are logic symbols other than AND

and OR, they all incorporate solid-state devices, For

auxiliaries operate over a wide range of speeds. Since

more information on solid-state devices refer to NEETS,

the speed of a dc motor with a constant load varies

module 7.

almost directly with the voltage, stages of line resistance

are used to make speed changes and to limit the current

DC CONTROLLERS

at starting. These stages of line resistance are connected

The starting of all dc motors, except those with

in various combinations, manually selected by a master

fractional horsepower, requires a temporary placing of

switch operating with a magnetic controller. Thus, the

resistance in series with the armature circuit to limit the

operator directly controls the amount of resistance in the

high current at start. The starting resistance cannot be

line and the resulting speed of the motor at all times.

removed from the line until the motor has accelerated in

One-Stage Acceleration

speed and the counter electromotive force has increased

Figure 1-14 shows a typical dc controller. The con-

to limit the current to a safe value.

Auxiliary motors located below deck generally

nections for this motor controller with one stage of

drive constant-speed equipment. A rheostat in the shunt

acceleration are shown in figure 1-15. The letters in

field circuit may be provided to furnish speed control

parentheses are indicated on the figures. When the start

for motors operating with ventilation fans, forced draft

button is pressed, the path for current is from the line

blowers, and certain pumps where conditions may

terminal (L2) through the control fuse, the stop button,

require operation at more than one speed.

the start button, and the line contactor coil (LC), to the

line terminal (L1). Current flowing through the

Small motors use one stage of starting resistance in

the line for a few seconds to limit the starting current.

contactor coil causes the armature to pull in and close

With larger motors, two or more stages of resistance are

the line contacts (LC1, LC2, LC3, and LC4).

Figure 1-13.-A static logic panel for a cargo elevator.

1-10