Temperature Sensor

Junction box and transmitter

Converts the raw resistance or millivolt signal to a standard 4-20 mA or digital bus signal, usually intrinsically safe for use in a cargo tank atmosphere.

Console interface

Displays the reading alongside level and, on many installations, feeds the cargo calculation system directly so loading computers can compute weight and trim without manual entry.

Selection and sizing

Regulations and class

There is no single SOLAS chapter dedicated to cargo temperature measurement, but class rules for tankers and gas carriers require the cargo control system to display tank temperature where the cargo is temperature-sensitive, and the IGC Code expects temperature monitoring on cargoes carried refrigerated or under pressure. Custody transfer installations are commonly calibrated and verified against a traceable standard at intervals set by the operator's quality system rather than by a single fixed rule, and class surveyors will ask to see that calibration record at survey.

Typical faults

• Element drift over years of service, causing a small but consistent offset that only shows up when checked against a portable reference
• Moisture ingress into the junction box, producing an erratic or fluctuating reading rather than a clean failure
• Cable damage inside the tank from cargo agitation or mechanical cleaning equipment, giving an open-circuit or short-circuit fault
• Ice or wax build-up around the sensing element on cold or waxy cargoes, slowing the response so the display lags the real temperature
• Wrong element type fitted after a spares mix-up, giving a reading that looks plausible but is quietly out of calibration

What to look for in a supplier

• Certified accuracy figures with a calibration certificate traceable to a recognised standard, not just a datasheet claim
• Ex-certification matching the tank's actual zone, with documentation the class surveyor will accept without query
• Element and cable materials proven for the specific cargo range, cryogenic or heated, rather than a generic mid-range product
• Spare element availability that does not require replacing the entire probe assembly

Check the temperature reading against a portable calibrated thermometer at the manifold or sample point before trusting it for a custody transfer figure — a drifted sensor rarely fails outright, it just quietly costs money on every cargo.