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Scientific news from Division 1 |
In-situ testing of domestic water meters will soon be possible
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First positive results of a joint research project of PTB and verification authorities show that in-situ water meter testing is technically feasible and serve as a basis for a corresponding extension of the existing provisions for in-service testing.
Any person being in doubt about the proper functioning of his/her water meter at home can apply for an in-service testing at the respective verification authority or supply company. At present for such an in-service testing, the water meter is demounted and metrologically tested on a test rig. Thereby, the test conditions are "idealised" and not always identical to the real installation and operating conditions of the meter in situ. This problem is particularly relevant in the case of so-called cartridge meters. Their housing is often flush-mounted so that it cannot be removed. In this case, only the measuring cartridge (e.g. the inner part of the housing, the impeller and the register - see fig. 1) is removed and then tested in a special manifold on the test rig.
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Figure 1: Section of a cartridge impeller water meter |
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In 2003 already, the insufficiency of this method prompted the Working Committee for Metrology and Verification (AGME) to the decision that domestic water meters which cannot be completely demounted should be tested in-wall. But the technical and legal core conditions for the implementation of this decision were not given at that time.
PTB's Liquid Flow Department along with representatives of the verification authorities are now successfully working on the solution to this problem within the scope of a research project.
On the occasion of a progress report, the following results were presented:
- Proof that the in-situ testing of domestic water meters is technically feasible using different measuring methods
- Development and testing of suitable reference standards
- Elaboration of corresponding work instructions and flowcharts for the testing
- Agreement on the way in which the in-service testing of meters which cannot be completely removed should be carried out as a rule.
The diagrams in figure 2 show the results (error curves) for two different cartridge water meters which were tested both in-situ and on the test rig of the respective verification authority. In particular the second example illustrates the insufficiency of the in-situ testing method applied up to now (demounting of the measuring cartridge and testing in a manifold only) when installation effects are obviously the reason for the incorrect measurements of the meter. Although in this case, the in-wall mounted meter indicates between 14 % and 18 % too much, the measurements on the test rig in a manifold remain clearly within the maximum permissible errors in service - the incorrect measurements at the customer's water meter installation would thus not be "discovered".
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Bild 2: Error curves of cartridge water meters after in-wall and rig testing |
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The global task of the research project comprises the development of transfer standards not only for the in-situ testing of domestic water meters but also as comparison standards for water meter test rigs of verification authorities, state approved test laboratories and the PTB and as standards for the "wet" volume determination of measuring vessels of more than 10.000 litres. The subject with all its subtasks is planned to be completed by September 2006.
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Contact person: |
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Gudrun Wendt, FB 1.5, E-Mail: gudrun.wendt@ptb.de
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© Physikalisch-Technische Bundesanstalt
Page created: 15.11.2005, last update: 15.11.2005, Dirk Röske
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