Metrology deals with the study and application of measurements – not to be confused with meteorology, the study and the prediction of weather patterns! According to NPL UK (National Physical Laboratory UK), “Metrology covers the accuracy, precision and repeatability of a measurement. It involves traceability or comparison with a ‘standard’ or between different measuring systems.” For example, any unit of measurement must conform to international specifications – a meter or a litre should be identical whether measured in Zimbabwe, France or the USA. Measuring systems are never perfect – they are subject to environmental variations such as temperature, pressure and humidity and so measuring instruments must be calibrated – the art of metrology. Comparisons can be used to set standards that are traceable and repeatable. Measuring instruments need to be calibrated (checked) to ensure that they are as accurate as possible.
There are three main areas of calibration services. Scientific or laboratory metrology is concerned with the establishment and standardisation of units of measurement. Industrial metrology focuses on the specifications and dimensions of manufactured products as well as quality control. Legal metrology is the enforcement sector dealing with the regulation and statutory requirements for measuring instruments and methods of measurement. In effect it deals with the enforcement of the government’s Trade Measures Act ensuring measurements of volume, mass and length and correctly assessed.
Maxwell Makamba, founder of Calibration Technology Systems, is a leading expert in the field with many years of training and experience. The company specialises in the measurement of fluids, in particular fuels like petrol and diesel. Their scope of work focuses on volumetric calibration primarily for fuel dispensing pumps at service stations, fuel storage tanks – ensuring that the volume of fuel dispensed correlates to the amount of fuel remaining in the tank – loading and unloading of road tankers to ensure that no fuel is lost in transport, Coriolis and Electromagnetic flowmeters and water meters.
Makamba initially studied at the Harare Polytech and achieved a Bachelor of Technology degree in 1993 where he developed his passion for metrology. He later joined the Trade Measures Office under the Ministry of Industry and Commerce. He underwent further training becoming an Inspector of Trade Measures. He joined NDT (Non Destructive Testing) and became the Calibration Supervisor. After many years of working experience he set up Calibration Technology Services in 2019.
A major area of their work is checking and calibrating the fuel dispensing pumps at service stations. They use carefully assessed 5 and 20 litres tanks to measure the amount of fuel dispensed and ensure that it correlates with the amount shown on the pump. Errors of 0.5% are permitted but only in excess in order to protect the public. Once the pump meter has been correctly adjusted and calibrated a seal is fitted to ensure that there is no tampering with the meter after the inspector has left. If the pump needs to be repaired only an accredited technician can break the seal and then the dispensing pump needs to checked and calibrated again and a new seal fitted. Commercial pumps need to be calibrated at least once a year or on request by the owner or a member of the public.
Underground fuel storage tanks are similarly calibrated to ensure the amount of fuel dispensed matches the amount of fuel left in the tank. By not returning the dispensing nozzle to the pump, which automatically returns the pump reading to zero, service station attendants can effectively illegally swindle customers out of the correct of amount of fuel for their own benefit. Measurements of the amount of fuel in the tank are taken several times with dip sticks and calculations are made to ensure the quantities tally up correctly. Calibration Technology Services also holds training courses for fuel attendants at service stations, mines, transport companies and other institutions to ensure that best practices are adhered to. Attendants are trained, amongst other things, to calculate the quantity of fuel taking into account temperature variations. Liquids expand when it’s hot and contract when it’s colder so calculations need to compensate for temperature fluctuations. Underground tanks need to be calibrated at least every ten years to account for the tanks tilting or subsiding underground which would make dip measurements inaccurate. They also need to be pressure tested to ensure there is no leakage.
Road tankers need to be similarly inspected at least every two years and the pump meters used for loading and unloading calibrated to ensure no fuel is lost in transit. Road tankers generally have their tanks divided into several compartments with a pipe or manifold connecting the different compartments to a single outlet for offloading. The quantity of fuel in the compartments is calculated in similar way to underground tanks with dipsticks. Sometimes an Ullage bar is used in conjunction with a dip stick. An Ullage bar measures the empty space in a tank to calculate the amount of fuel in each section. It’s considered more accurate than a dipstick and calibration needs to be confirmed by an inspector. Once a tanker is loaded the outlet is closed with a seal to ensure there’s no tampering until the tanker is ready to be unloaded. However, some enterprising drivers worked out a way to open the outlet valve without breaking the seal by unbolting the handle which opens the valve. They were then able to able to drain fuel from the manifold without affecting the amount of fuel in the tanks. Makamba came up with a simple and ingenious way of preventing this leakage by tack welding the bolts on the handle so it can’t be opened without breaking the seal. This has saved transport companies substantial amounts of money!
The National Metrology Institute of Zimbabwe (Custodian of National Measurement Standards) sets the parameters for measuring units with the greatest degree of accuracy – they are affiliated to the South African National Standards. The NMI sets National Standards which in turn set local working standards which are verified every year.
According to Wikipedia, metrology has a wide ranging impact on our daily lives, “including economics, energy, environment, health, manufacturing, industry and consumer confidence. The effects of metrology on trade and economy are some of the easiest-observed societal impacts. To facilitate fair trade, there must be an agreed-upon system of measurement.”
Text: Michael Nott
From: E&P ISSUE 11