Sensors are fitted so that the temperature of the cargo can be monitored in order to:
- Ensure that cargo heating requirements are complied with; Ensure that any tank structure and tank coating temperature limitations are not exceeded; and
- Calculate the weight of cargo on board (the specific gravity of a product varies according to temperature).
- Sensors may also be fitted to monitor the temperatures of the structure around the cargo system.
Types of thermometers
Liquid/vapour thermometers rely on the expansion or contraction of liquid in a very fine bore calibrated tube or capillary. It is important to ensure that the liquid column in the instrument is continuous, otherwise the reading will be inaccurate.
Bi-metallic thermometers consist of two metals with different coefficients of expansion. Bimetallic thermometers are susceptible to vibration and should only be installed in positions that are free from this effect.
Thermocouples rely on heat applied to the junction of two dissimilar metals generating a very small voltage which can be measured. A change in voltage output will indicate a change in temperature.