The level measurement range is over 220mm and takes place inside a small chamber off the side of the large frying vessel, each mm represents 100’s of litres of cooking oil. It is important that the whole range is measured, both during charging of the oil and heating of the process as well as in full production. Heat input needs to be carefully controlled in any fryer system for optimal efficiency and safety.
The engineers initially tried a high-temperature guided wave radar, but discovered that this measuring principle has physical performance limitations when working with poorly reflecting liquids (oil-based products) in small vessels. This is because oil is a poor reflector and not easily detected at extremes of the range, resulting in only the middle part making an accurate measurement over this short length. In its place a capacitance probe was installed with some success; it has no moving parts and detected the oil over the full measuring range. However, the oil changes in dielectric (conductivity) as it heats and cooks the chips – (due to changing carbon levels in the oil) which directly affects the level accuracy of this type of probe.