There are four methods to fight the magnetic impacts to electricity meters:
The field of the magnet makes weak quickly while distance is increasing between it. The field of the neodymium magnet showed at the picture.
We can see at the picture, that induction with a strength of 100mT, that is normal condition for testing the electricity meters, is limited with the area that is approximately equal to two heights of the magnet from its’ surface. So, the simplest way of protection from the magnets – sealed up box. The more the distance from electricity meter to the walls of the box, the more the meter is protected. Small box cannot protect the electricity meter from the impact of a large magnet.
- Magnetic fields. Shielding.
Second way of protection of electricity meters – shielding of the meter or it’s units. As it showed at the picture, the force lines of the magnetic field are closed-loop by the iron of the shield and only insignificant part goes through it.
You can watch a video. Two powerful neodymium magnet can not stop the electricity meter, if it was protected by an iron screen.This video shows how much can be a reliable screening.
Now the outer magnetic shielding is rarely used, because it is necessary to use a large size outdoor shield with a wall thickness up to 5 mm. The small shield with significantly thinner walls can be set into the electricity meter to achieve the same result. It is necessary to protect only some weak places of the electricity meter. This method is used by developers of meters, and with the right design meters are well protected from strong permanent magnets.
- Magnetic impact indicators.
Third widespread method to resist thefts – magnetic level indicators. We can talk a lot about different indicators. They have advantages and disadvantages. Unfortunately, even a perfect indicator controls magnetic field only where it is placed. That is why several indicators are installed in the electricity meters to defend it from different sides.
There are magnetic level indicators built in the water meters and electricity meters that likely point out to disadvantages of the meters – so, obviously, designers didn’t choose the way of development non-sensitive to magnetic field device, instead, they chose easy way of setting magnetic impact indicators.
External indicators, stickers on the meter – is an ineffective way which have had to resort to protect the old type meters. It only reduces the thefts temporally by additionally investing.
- Design of the electricity meters
Using of protected meters is the most reliable solution of problem of magnetic impacts. Electricity meter should not contain elements if work capacity of such elements depends on powerful magnetic field. There are many types of electricity meters that work and are not influenced by even very strong magnetic fields.
Text has been updated November 15, 2018 by the author: