Page 348 - Introduction to Marine Engineering

Instrumentation and control 32!

The timing of certain events, such as the opening and closing of steam
valves, must be carefully controlled to avoid dangerous conditions
occurring or to allow other system adjustments to occur. Protection and
safety circuits or interlocks would be input to the programming and
timing unit to stop its action if, for example, the turning gear was still
engaged or the lubricating oil pressure was low. The ahead/astern
selector would direct signals to the appropriate valve controller resulting
in valve actuation and steam supply. When manoeuvring some switching
arrangement would ensure that the astern guardian valve was open,
bled steam was shut off, etc. If the turbine were stopped it would
automatically receive blasts of steam at timed intervals to prevent rotor
distortion, A feedback signal of shaft speed would ensure correct speed
without action from the main control station.

Safety
checks

Figure 15.44 Bridge control of slow-speed diesel engine

A bridge control system for a slow-speed diesel main engine is shown
in Figure 15.44. Control may be from either station with the operating
signal passing to a programming and timing unit. Various safety
interlocks will be input signals to prevent engine starting or to shut down
the engine if a fault occurred. The programming unit signal would then
pass to the camshaft positioner to ensure the correct directional location.
A logic device would receive the signal next and arrange for the supply
of starting air to turn the engine. A signal passing through the governor