Weighing solution for water flow measurement
Weighing platforms support the conversion of heating cost measurement
The National Institute of Metrology in Beijing was faced with the task of laying the foundations for documenting the hot water consumption of individual users. The new calibration system was to employ flow and temperature to determine usage. A precise weighing solution for different capacities was successfully implemented
- High level of accuracy
- High IP rating for rough operating environments
- +/-2 d repeatability
- Quick and easy built-in calibration and adjustment feature/function
"The new facilities open a window on heat meter calibration, whilst also modelling the fantastic quality of Minebea Intec’s products."
Mr Zhang Lihe
National Institute of Metrology (NIM), Beijing
In 2010, the Chinese government adopted new criteria to calculate utility bills, moving away from using the surface area of dwellings to instead charge on a hot water consumption basis. For that purpose, 20 million RMB (about €2.5 million) was invested for the construction of a 1,800 m² laboratory. The National Institute of Metrology (NIM) was appointed to oversee the development of a suitable infrastructure that would lead to the installation of three million water meters every year.
Since water would reach the homes already heated, the calibration system would have to analyse flow and temperature to determine energy consumption, while keeping uncertainty below 0.1% and supporting a maximum flow rate of up to 600 m³/h.
The most accurate way to analyse water flow is by determining mass. Therefore NIM approached Minebea Intec for the supply of high-resolution scales with the following requirements:
- Three capacities of 60 kg, 600 kg and 6,000 kg
- Excellent repeatability and linearity
- Accuracy better than 0.01%
- Resolution higher than 120,000 d
- High IP ratings for adverse environment conditions
- Digital displays with inherent abilities to reduce communication interference
The solution Minebea Intec proposed was the range of high-resolution scales with IS weighing platforms, which is based on Electromagnetic Force Compensation Technology (EMFC). With EMFC, the weighing platform is connected to a lever with a coil (with current flowing through it) floating inside of a permanent magnet. Whenever a weight is placed on the scale, the lever moves and the increase of current in the coil generates a compensating magnetic force to maintain its initial position. The amount of generated force (the increase of the current in the coil) then translates into a weight readout.
The scales were built with high-quality stainless steel with IP67 ratings and were connected to a series of Combics 3 weight indicators equipped with an IP69K rating and RS485 serial interface. They also allowed for repeatability of +/-2 d, and a quick and easy built-in calibration and adjustment of the weighing system without weights. This approach resulted in much more accurate weight readouts, with a resolution of 600,000 d, which was well above the 120,000 d required by the customer.
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