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Factors which may affect measurement by Automatic Level Gauges

• Lack of use - mechanical ones can seize up.
• Low levels in the tank - some gauges can stop working below a certain level and do not take account of liquid being received into, or discharged from the tank, whilst measurement is in progress.
• Rust - unlikely in an oil environment - but this can happen to mechanisms where their parts or components are regularly exposed.
• Turbulence - although many ALGs are designed to dampen down turbulence and to find the true level even though the top surface could be rippling.
• Temperature - oil can form layers at different temperatures. Some meters compensate for this by having an averaging beam that takes and averages temperature measurements at a range of different depths across layers.
• Tank Dips - see HCOTEG177700, because an ALG is effectively an automatic dipping machine, the same provisions apply.

Automatic Level Gauges - other considerations

ALGs have to be fitted and adjusted to each tank, and their measurements must be converted by a calibration table which has been compiled and tested uniquely for each tank (this is most likely to be done electronically).

»Ê¹ÚÌåÓýapp fixings of the meter and all equipment that is used to adjust and maintain the meter and the read-out system also need to be controlled effectively by the trader in order to stop fraudulent interference.

Warehouse-keepers should have a control system in place that regularly (usually monthly) compares the ALG to a manual dip/ullage. Any differences outside of the agreed tolerance (currently +/- 8 mm) should be investigated and corrective action taken.

Please note that all new equipment installed after October 2006 should meet the new accuracy tolerance of +/- 5mm when compared to the results of manual dipping.