The tank level telemetry system is an important part of ship automation, used to monitor the liquid level in ballast tanks, fuel oil tanks, fresh water tanks, sewage tanks and other compartments in real time. A reliable level telemetry system must not only measure accurately but also operate stably over long periods in harsh environments of moisture, vibration and corrosion. Jiangsu Haizhongzhou Shipping Industry Co., Ltd. has established a complete signal link quality control system from sensor to control room in the selection, installation and commissioning of level telemetry systems.
Sensor selection depends on the medium properties and tank structure. For ballast and fresh water tanks, Haizhongzhou prefers submersible hydrostatic level transmitters. The transmitter probe is installed at the lowest point of the tank bottom, and the liquid level is calculated by measuring the hydrostatic pressure of the liquid column. The probe material is 316L stainless steel or duplex stainless steel, and the cable is sheathed with polyurethane or PTFE for seawater corrosion resistance. For fuel oil and lubricating oil tanks, magnetostrictive level gauges or radar level gauges are used, because oil media may block the pressure tapping port of a hydrostatic probe. The float of a magnetostrictive level gauge rises and falls with the liquid level, achieving accuracy of plus or minus one millimetre, suitable for applications requiring precise fuel consumption measurement.
The installation position of the sensor directly affects measurement accuracy. Haizhongzhou requires that hydrostatic probes be installed away from ballast pipe outlets, agitator vortex zones and structural stiffeners to avoid turbulence and bubble interference. A gap of at least fifty millimetres is maintained between the probe and the tank bottom to prevent sludge accumulation from covering the probe. For large tanks, Haizhongzhou installs multiple measuring points and takes average values to avoid measurement distortion due to vessel heel or trim.
The signal transmission link is the neural network of the level telemetry system. The 4‑20 mA analogue signal or RS485 digital signal output by the sensor is transmitted through shielded cables to the acquisition module. Haizhongzhou imposes strict requirements on signal cable routing: the distance from power cables must be not less than 300 mm, separate metal cable trays or conduits must be used, and the shield must be grounded at a single point on the control room side. For long‑distance transmission (exceeding one hundred metres), Haizhongzhou adds signal isolators or converts to fibre‑optic transmission to prevent signal attenuation and electromagnetic interference.
Level display and alarm functions in the control room are the final output of the system. Haizhongzhou displays the liquid level of each tank graphically on monitoring computers on the bridge and in the engine control room, using different colours to distinguish normal, high and high‑high conditions. A high level alarm alerts the operator to stop filling, while a high‑high level alarm triggers an audible/visual alarm and automatically closes valves or stops pumps to prevent overflow. During commissioning, Haizhongzhou performs a water filling test on each tank, measuring the actual liquid level with a sounding rod and comparing it with the telemetry system reading, requiring a deviation not exceeding one percent of full scale. All alarm points are verified one by one to ensure that the alarm setpoints are accurate and the response is timely.
