§ 19 The principle of the operation of electronic meters.

The article was taken here: http://www.railway.te.ua/pc_meter.htm

Microprocessor energy meters.

Hello, dear reader. On this page we briefly, so as not to bother you much, we will consider microprocessor counters for electricity metering. The main difference between such counters and conventional induction ones is that they are a small "on-board computer". In such counters, there are practically no moving parts that measure the current consumed. The meter usually consists of measuring current and voltage sensors (transformers with improved characteristics), measuring circuits (ADC - analog-to-digital converters), microcontroller processing digital signals, memory for storing the counter data. All the information of the counter is displayed on the liquid crystal display. Counters are usually powered from the voltage circuits connected to them. In addition, it is a good idea to install backup power on the meter (in the form of various batteries). They are designed to maintain the integrity of important information when the meter is disconnected from the power circuits. The values ​​of the current consumed are determined by means of current transformers. Further, the current and voltage signals are multiplied through the ADC on a high-performance microprocessor with a RISC-instruction set. All received information is stored in the memory of the counter and displayed in parallel on the liquid crystal display. The simplest scheme of the counter is shown in Figure 1.

A simple scheme for measuring the MP counter

In addition, additional information outputs (current loop, pulse number, in which the pulse frequency is proportional to the consumed electricity, RS-485 output, etc.) can be input in various counter models. Practically in all counters there is a memory for storing the program of operation of the meter, the measured values ​​(ie, active and reactive energy), as well as a list of various significant events (the number of inputs to the counter, power failure, transition to winter and summer time, etc. ).

A distinctive feature of such meters is the ability to account for electricity at tariffs. This means that you can pay for consumed electricity in different ways. For example: there are 3 tariffs for calculating electricity - peak (usually morning and evening hours), semi-peak (it's almost all day except morning and evening) and night. The price for consumed electricity varies depending on the tariff. At a single-rate tariff of 1 kWh, it costs 0.1271 UAH, if you decide to pay by tariffs, you will need to multiply this price by the following factors:

- peak tariff - 1.8
- semi-peak tariff - 1.02
- night rate - 0.2

Obviously, it is most profitable to work at night rates (the price for 1 kWh is 4 times less). In the old induction counters, you could not account for the transitions to different time tariffs (for this you would have to put a person at the counter that watched when the peak tariff comes and wrote down the testimony). As an output it would be possible to use a computer system for collecting information in real time and then manually dividing into intervals at tariffs. However, it is much easier to put a microprocessor counter, whose internal program would itself monitor the transition from one tariff zone to another and record the energy consumption separately for each interval.

In addition, such a counter can be a good diagnostic tool. For example, the meter "Alpha +" of ABB VEI Metronica (Moscow, Russia) can work as a VAF (volt-ampere-phase meter), show the current value of current and voltage, harmonics, etc. (See figure 2).

Alpha +

Counter of ABB VEI Metronica

Schedule of electricity consumption

Example of power consumption graphs.

Window program counter Alpha +

Figure 2. A copy of the screen of the counter program "Alpha +".

In addition, given the high accuracy class of such counters (0.2-0.5) and the lack of self-propulsion (ie self-movement of the disk, as in an induction meter), we can say that today such counters are the most convenient option for electricity metering .

In order for the counter to read and write data to it, it is necessary to make a program that will "tell" the counter what to do: how to measure, what to measure, where and in what form to write. To do this, you must have a personal computer with a special program supplied with the counters, the counter itself, a special analyzer for transferring data from the computer to the counter. And, by and large, all the counters are programmed according to the same rules: the user does not need to write programs in any programming language - all that is required of him is just to answer the questions of the program and to mark the necessary options for the counter's work with the mouse. An example of the program window for the "Quantum D300" counter of the Schlumberger company (ryunok 3).

The counter of Schlemburge

The counter programming screen

One of the useful properties of these meters is the possibility of creating on their basis an information system for collecting and processing data on electricity consumption. Those. You can create on the basis of such counters an automated system for collecting information. Suppose you have several objects (substations or small factories for the production of products) and you want to control the power consumption of the facilities. There is nothing simpler - you put the microprocessor counters on the accounting points, connect a modem (impulse relay, RS485 output) to them and collect all the information on one PC, standing in your office. Even if you need to reprogram the counter - you can do this remotely, via a modem. And then immediately the question arises: And if I'm a "bad person" and want to get in and change the data in the counter? On this account, the counter has its own "answer to Chamberlain". Usually counters have several levels of access to their information (for reading, for modification, for reprogramming). In addition, the memory of the counter contains information about all attempts to read and enter it. So you can determine when the data in the counter changed.

Here, dear reader, I end my story so that you can rest a little. Next time we will talk with you and various automated systems that can be built on the basis of microprocessor counters. Sergey Kibitkin.