Electrical and electronic systems on board — from relay control to CAN bus.

A modern ship is not just mechanics and hydraulics — it is also filled with electrical and electronic systems that control monitor and protect the machinery. As a ship fitter you must be able to perform basic troubleshooting and repair on electrical systems and control and monitoring systems based on knowledge of electrical diagrams and you must have knowledge of relay control systems and the standards used for data exchange between systems.

§Relay controls – the classical automation

A relay controller uses electromechanical relays to turn circuits on and off depending on which signals come in — for example from a pressure switch or a temperature sensor. Although many newer systems are digital relay controls are still widely found on board and being able to read an electrical diagram and understand how the relays connect is a fundamental skill when a control system needs to be troubleshot.

§From analogue measurement to digital data

Modern ships use a sea of sensors for temperature, pressure, level, flow and vibration. You should be able to use a multimeter to measure both analogue and digital sensors and transmitters — for example a temperature transmitter, a level gauge or a revolution counter — and you should have a basic understanding of how a signal is converted from analogue to digital (A/D conversion) and how data is then processed in a hardware architecture with processor, memory and input/output devices.

• 01Multimeter — the basic tool for measuring voltage, current and resistance on sensors and transmitters
• 02Analog sensors – deliver a continuous signal (e.g., 4-20 mA) for pressure or temperature
• 03Digital sensors/transducers — deliver the signal as digital data directly
• 04A/D conversion — converts an analog signal to a digital one the computer can process
• 05CPU, memory and I/O — the hardware that processes and forwards the measurements

§CAN bus — the network that binds the systems together

Instead of running a separate cable between each sensor and instrument, modern ships and vessels use a shared digital network that the instruments are connected to. The NMEA 2000 standard is such a network for marine electronics, built on CAN bus technology (Controller Area Network) — the same basic principle also used in cars. The network is structured as a shared line (a 'backbone'), where engine instruments, navigation equipment, autopilots and monitoring units can all exchange data over one cable system instead of individual point-to-point connections.

§Troubleshooting on electronic systems

When an electronic system acts up, you start with the simple: is there power, are fuses and connections intact, and does the instrument show a sensible number? Next, you follow the signal path from sensor to display, and you use test equipment to determine if the fault is in the sensor, in the wiring, or in the control unit itself. Basic troubleshooting of digital and analog electronics therefore requires both broad technical knowledge and a calm, systematic approach.

Digital tools and artificial intelligence are increasingly part of this part of the trade — for searching technical information and to support troubleshooting — but it does not change that you yourself must be able to critically evaluate the result professionally and competently before you act on it.