§5 How does an electric meter work?
Usually for the tenants the meter is presented in the form of a “black box” through which the wiring goes to the apartment. This “box” in some way, in a known way, can count the amount of electricity that has passed through it, for which we are sometimes 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, you can learn something new. .
What, or what, makes that aluminum disk spin in the meter. Maybe there is a small motor there that drives your spent kilowatts? Can he spin just like that, by himself? Well, dear reader, I sadly inform you that we will have to dive briefly into the wilds of physics and electricity.
Let's take a look at the drawing. The movable part of the counter consists of an aluminum disk 1, planted on axis 2. To dampen the oscillations of the moving part, a permanent magnet 4 serves. The torque of the disk is formed by electromagnets 3 and 4. The electromagnet 3 has a current winding connected in series with the measured load and along it a current passes, creating a magnetic flux (for simplicity, let us imagine that this is some field that appears when current passes through a conductor). The magnetic flux passes through the disk twice, closing up through the details of the magnetic circuit 4 and forming two streams in the gap. There is such a rule, called the “left hand rule.” If you position the palm so that the magnetic field lines enter it, and the extended fingers indicate the direction of the current, the loosened thumb will indicate the direction of the force acting on the conductor.
The horror, while reading this rule, almost got tired. If you do not understand anything, then in general this means the following: a current flows through the meter coil, magnetic flux appears, and as a result, we have the power to twist the meter disk in a certain direction. This rule is used by some bad people trying to trick the counter, 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 disc changes.
Recently, new-generation electric energy meters, microprocessor-based, began to appear. Their main difference is not so much the principle of obtaining data (current and voltage transformers remain transformers), but a processing mechanism, access to the obtained data. In these counters there is no disk, which is spinning, in them analog-to-digital converters (ADC) and microprocessor (MP) make a sample of current and voltage to obtain the final result displayed on the counter display.
Microprocessor electricity meters (firms Schlemburge left and ABB right).
- Accounting for multi-tariff mode (i.e., the meter counts for different prices during peak hours, night and semi-peak hours);
- Many options for access to the meter (via modem, current loop, RS485 \ 232, etc.);
- A large number of additional parameters displayed by the counters (within a hundred) - peaks, load graphs, tariff calculations, average values, etc .;
- The accuracy class of such meters is higher (i.e., better) by an order of magnitude than induction 0.2, 0.5 versus 2.0 induction. However, for this purpose, in the accuracy class there should be transformers to which such meters are connected.