In the final installment of this three-part series, authors Adam Kozlowski and Janusz Dubicki reference other utility markets that are similarly subjected to possible magnetic field influence and metering inaccuracies. (Commercial and residential water meters launched this series on magnetic field impacts on metering results.)
Part 3 below concludes this series with the aim of understanding meter design and developing metering solutions that counteract magnetic field interference whether such inaccuracies can be attributed to a meter’s inherent design vulnerabilities or traced to intentional tampering that might falsify results.
Crime Stopper (Part 3) By Adam Kozlowski and Janusz Dubicki
The fight against water theft with the use of strong magnetic field
How do you protect your meter network from losing its measuring capability? One option to improve and protect measure devices like dry-dial water meters is to use passive magnetic field indicators to detect the action of a strong magnetic field primarily coming from neodymium magnets. These indicators are especially useful for water meters already in use in networks (external installation), but in the case of new water meters, the passive magnetic field indicators can, by design, be installed also inside the device. The indicators are also used to detect a strong magnetic field action on other vulnerable measuring devices, like watt-hour meters and gas meters.
Other Media Measuring Devices Under Influence of Neodymium Magnet
A strong magnetic field also negatively influences the correct operation of other measuring devices than dry dial water meters. Watt-hour meters and gas meters belong to these devices. There are two types of watt-hours meters: induction and electronic.
Induction watt-hour meters have found such applications as residential meters and electronic watt-hour meters are especially applicable as commercial meters, but it is considered that electronic metering solutions can also provide the residential energy market with the accuracy, flexibility, and networking benefits currently unavailable in most locations.
The most susceptible elements in induction watt-hour meters to NdFeB magnets are the magnetic circuits of current and voltage coils and the braking magnets of aluminum rotor disks (EMC Defect in watt-hour meter [Ferraris] operating in strong stationary magnetic field 2006). By putting a neodymium magnet near the measuring coils of a meter, the meter reading is lower than the real electric energy consumption; it means that the measuring error becomes negative.
However, after removing the magnet from the meter, its indication returns to its correct measuring class. In this case, the interference process is reversible. An attack with a strong external magnetic field on the braking magnet of the meter can lead to its demagnetization and, what follows, to irreversible changes of the measuring characteristic of the meter.
As a consequence of these changes, the aluminum disk spins faster than it should, and the meter reading is higher than the real energy consumption.
The popularity of the electronic watt-hour meters is growing because of its numerous measuring-visualization functions. Many different kinds of electronic watt-hour meters are known, depending on measuring process applied. Even though the measuring process differs in various kinds of meters, it does not change the fact that meters are equipped with different common subassemblies, which are susceptible to a magnetic field, no matter which measuring process is used. It especially concerns electronic watt-hour meters using susceptible current transformers for current measurements. Their magnetic characteristics are linear in the whole range of their normal operation.
However, the influence of a strong external magnetic field leads to a change of the current transformer magnetic characteristics. The idea is to saturate the core of the current transformer or distort the flux in the core with the use of a neodymium magnet (like in the case of induction watt-hour meters current and voltage coils). This procedure results in less billing because of lower electric energy consumption reading.
The phenomenon is reversible—the meter indication returns to its normal measuring class after removing the magnet. The above-mentioned additional common subassemblies of electronic watt-hour meters are mechanical counter stepper motors, transformers supplying electronic circuits, and electric rate switches.
If these elements are under the influence of an external magnetic field, it can lead to a total cease of counting consumed electric energy. For electronic watt-hour meters, the phenomenon of magnetic field action by using neodymium magnets is reversible and does not damage the meter. It makes it possible to corrupt electronic watt-hour meters, the detection of which is very difficult if passive magnetic field indicators are not used.
The problem of magnetic non-resistance also concerns bellows gas meters, used for residential and commercial gas consumption measuring. The internal construction consists of diaphragms—bellows, which are moved by flowing gas. Each cycle of their work, measuring the same volume of gas, is transferred by a crank mechanism to a gear and counter.
In the case of gas meters equipped with diaphragms, which parts are made of ferritic steel, not plastics or aluminum, putting a neodymium magnet against the gas meter disrupts a regular operation of its mechanism. This manifests itself by temporarily attracting and holding down the diaphragm by the magnet, and then—by a release of the diaphragm under flowing gas. This irregular operation of the gas meter leads to a limitation of gas flow and, in practice, manifests itself in a weak flame in such appliances as gas cookers, water heaters, gas ovens, etc., causing, even, an overestimating of the gas consumption reading.
After putting the neodymium magnet against the gas meter, it can come to the situation when the flame goes out in operating gas appliances and, after a removal of the magnet, gas can begin to escape. (It is very dangerous.) However in many cases, depending on the placing of gas meter valves and diaphragms at the moment of putting the magnet, there is a possibility of non-throttled gas flow (not controlled by a counting mechanism) that is tantamount to gas theft.
Conclusions
The fastest method to improve the protection of measuring devices, including dry dial water meters, as well as other measuring devices, from a strong magnetic field is to use passive magnetic field indicators. This method is especially useful for devices already in use in networks.
Although many companies manufacturing measuring devices have taken many initiatives (e.g., presented in chapter 4), usually it turned out that the devices are not properly shielded to protect them from magnetic field influence, and then detection of an external magnetic field is needed, e.g., by using passive magnetic field indicators.
In the case of new measuring devices, the passive magnetic field indicator can, by design, be installed inside the device so that the indicator would be visible through a transparent wall of the device. It is only possible during the production process of devices to install the indicators inside e.g., water meters, but not after their installation in networks.
There are two types of watt-hours meters: induction and electronic. Induction watt-hour meters have found such applications as residential meters and electronic watt-hour meters are especially applicable as commercial meters, but it is considered that electronic metering solutions can also provide the residential energy market with the accuracy, flexibility, and networking benefits currently unavailable in most locations.
The most susceptible elements in induction watt-hour meters to NdFeB magnets are the magnetic circuits of current and voltage coils and the braking magnets of aluminum rotor disks (EMC Defect in watt-hour meter [Ferraris] operating in strong stationary magnetic field 2006). By putting a neodymium magnet near the measuring coils of a meter, the meter reading is lower than the real electric energy consumption; it means that the measuring error becomes negative. However, after removing the magnet from the meter, its indication returns to its correct measuring class. In this case, the interference process is reversible.
An attack with a strong external magnetic field on the braking magnet of the meter can lead to its demagnetization and, what follows, to irreversible changes of the measuring characteristic of the meter. As a consequence of these changes, the aluminum disk spins faster than it should, and the meter reading is higher than the real energy consumption.
The popularity of the electronic watt-hour meters is growing because of its numerous measuring-visualization functions. Many different kinds of electronic watt-hour meters are known, depending on measuring process applied. Even though the measuring process differs in various kinds of meters, it does not change the fact that meters are equipped with different common subassemblies, which are susceptible to a magnetic field, no matter which measuring process is used. It especially concerns electronic watt-hour meters using susceptible current transformers for current measurements. Their magnetic characteristics are linear in the whole range of their normal operation. However, the influence of a strong external magnetic field leads to a change of the current transformer magnetic characteristics. The idea is to saturate the core of the current transformer or distort the flux in the core with the use of a neodymium magnet (like in the case of induction watt-hour meters current and voltage coils). This procedure results in less billing because of lower electric energy consumption reading. The phenomenon is reversible—the meter indication returns to its normal measuring class after removing the magnet.
The above-mentioned additional common subassemblies of electronic watt-hour meters are mechanical counter stepper motors, transformers supplying electronic circuits, and electric rate switches. If these elements are under the influence of an external magnetic field, it can lead to a total cease of counting consumed electric energy.
For electronic watt-hour meters, the phenomenon of magnetic field action by using neodymium magnets is reversible and does not damage the meter. It makes it possible to corrupt electronic watt-hour meters, the detection of which is very difficult if passive magnetic field indicators are not used.
The problem of magnetic non-resistance also concerns bellows gas meters, used for residential and commercial gas consumption measuring. The internal construction consists of diaphragms—bellows, which are moved by flowing gas. Each cycle of their work, measuring the same volume of gas, is transferred by a crank mechanism to a gear and counter.
In the case of gas meters equipped with diaphragms, which parts are made of ferritic steel, not plastics or aluminum, putting a neodymium magnet against the gas meter disrupts a regular operation of its mechanism. This manifests itself by temporarily attracting and holding down the diaphragm by the magnet, and then—by a release of the diaphragm under flowing gas. This irregular operation of the gas meter leads to a limitation of gas flow and, in practice, manifests itself in a weak flame in such appliances as gas cookers, water heaters, gas ovens, etc., causing, even, an overestimating of the gas consumption reading. After putting the neodymium magnet against the gas meter, it can come to the situation when the flame goes out in operating gas appliances and, after a removal of the magnet, gas can begin to escape. (It is very dangerous.)
However in many cases, depending on the placing of gas meter valves and diaphragms at the moment of putting the magnet, there is a possibility of non-throttled gas flow (not controlled by a counting mechanism) that is tantamount to gas theft.
Conclusions
The fastest method to improve the protection of measuring devices, including dry dial water meters, as well as other measuring devices, from a strong magnetic field is to use passive magnetic field indicators. This method is especially useful for devices already in use in networks.
Although many companies manufacturing measuring devices have taken many initiatives (e.g., presented in chapter 4), usually it turned out that the devices are not properly shielded to protect them from magnetic field influence, and then detection of an external magnetic field is needed, e.g., by using passive magnetic field indicators.
In the case of new measuring devices, the passive magnetic field indicator can, by design, be installed inside the device so that the indicator would be visible through a transparent wall of the device. It is only possible during the production process of devices to install the indicators inside e.g., water meters, but not after their installation in networks.
