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§5 How the electric meter is arranged

Usually for residents, the meter is presented in the form of a “black box” through which the wiring goes to the apartment. This “box” can be considered by some method known to him the amount of electricity that has passed through it, for which we sometimes get paid. I think that if you are a metrologist (a person who is professionally engaged in various measuring instruments), then you do not need to spend time reading this article, you already know everything, but if you are an ordinary person, read it, you may learn something new .

How, or what, makes that aluminum disk spin in the counter. Maybe there’s a small motor that drives your spent kilowatts? Could it just spin like that on its own? Well, dear reader, I am bitterly informing you that we will have to plunge briefly into the jungle of physics and electricity.

The principle of operation of the counter

Let's take a look at the drawing. The moving part of the counter consists of an aluminum disk 1, mounted on the axis 2. To calm the vibrations of the moving part, a permanent magnet 4 is used. The torque of the disk is generated by electromagnets 3 and 4. Electromagnet 3 has a current winding connected in series with the measured load, and through it a current passes, creating a magnetic flux (for simplicity, let’s imagine that this is some field that appears when a current passes through a conductor). The magnetic flux passes through the disk twice, closing through the details of the magnetic circuit 4 and forming two fluxes in the gap. There is such a rule, called the rule of the “left hand.” If you place your palm so that the lines of force of the magnetic field enter it, and your extended fingers indicate the direction of the current, then the set thumb will indicate the direction of the force acting on the conductor.

Left hand rule

The horror, while I read this rule, almost got tired. If you do not understand anything, then in general this means the following: current flows along the counter coil, magnetic flux appears, and as a result, we have the force that will turn the counter disk in a certain direction. This rule is used by some bad people trying to trick the meter by changing the direction of the current flowing. The rule of the "left hand" is triggered and here, the direction of the force acting on the disk changes.

Recently, new generation electric energy meters began to appear - microprocessor-based. Their main difference is not so much the principle of obtaining data (current and voltage transformers remain transformers), but the processing mechanism, access to the received data. These counters do not have a disk that is spinning, in them analog-to-digital converters (ADCs) and a microprocessor (MP) select the current and voltage to obtain the final result displayed on the counter display.

Schlemburger and Alpha Counters

Microprocessor electricity meters (Schlemburger companies on the left and ABB on the right).

  • Accounting according to multi-tariff mode (i.e., the meter considers the price differently during peak hours, night and half-peak hours);
  • Many options for access to the counter (via modem, current loop, RS485 \ 232, etc.);
  • A large number of additional parameters displayed by counters (within hundreds) - peaks, load schedules, tariff calculations, average values, etc .;
  • The accuracy class of such counters is higher (i.e. better) by an order of magnitude compared with induction 0.2, 0.5 versus 2.0 induction. True, for this in the accuracy class there must also be transformers to which such counters are connected.