Basics of Energy Meters

What is Energy Meter?

A device which captures the “units of energy” is called as Energy Meter. This is the basic definition of an Energy Meters. The only difficult part in this definition is “units of energy”.


Let’s describe this part in more detail.

What are Units of Energy?

To understand about the units of energy, one should have knowledge of Energy.

Definition of Energy Unit
Figure 1: 1 Unit = 1 kWh

The simplest definition for the Energy is “the product of power and time”. In other words “Power drawn by some load in a specific time” is called as Electrical Energy. Mathematical way of writing Energy is as follows:

Energy (E) = Power (P) X Time (T)

Or, E = P X T

Now, if 1 Kilo Watt of Power is drawn by some load for 1 hour continuously, “1 Unit of Energy” will be consumed. Mathematical explanation for the definition:

If Power Drawn = 1 Kilo-Watt, for 1 Hour;

Energy Consumed = 1 Kilo-Watt-Hour (kWH)

1 Unit = 1 KWH

The accurate measurement of these units is the key purpose of Energy Meters.

What is Maximum Demand Indicator (MDI) in Energy Meters?

Another important feature that is required by the Energy Meter is Maximum Demand Indicator (MDI). As its name suggests that MDI tells about the maximum demand load of a specific consumer. It is used to charge penalties to the consumers where consumers are using load more than the sanction load/ approved load. Moreover, it also helps in the long-term future load forecasting during the extension of electric infrastructure.

Graph of Maximum Demand Indicator
Figure 2: MDI (Maximum Demand Indicator)

To understand that how energy meters calculate MDI, let’s take an example of a home where everybody is in rush.  Someone is ironing his clothes with 1000-watt iron, at the same time a 1000-watt Air Condition is running. Other persons present in other rooms are using 3 fans of 100 watts each and lighting their places with 3 lights of 24 watts each. In short all electrical appliances of that home is running, it is the peak load time of that home. If this peak load time remains from 15 to 30 minutes, the energy meter will record the MDI of 2.372 kWatts.


Iron = 1000 Watts

Air Condition = 1000 Watts

3 Fans = 3 x 100 Watts = 300 Watts

3 Lights = 3 x 24 Watts = 72 Watts

Total Load at that time = 1000 Watts + 1000 Watts + 300 Watts + 72 Watts = 2372 Watts

I.e. MDI = 2.372 kWatts

Importance of Energy Meters:

These devices are the most important component for the electricity supplier companies. They play key role in revenue generation for these corporations. Old Energy Meters were only able to calculate Energy units but with the advancement of technology, numerous functionalities are added in it. In present complex electricity scenario, objective of an Energy Meter is not just capturing the Energy Units.

Some of the other objectives are:

  • Load Control
  • Load Management as per sanction load
  • Tariff Distribution
  • Indications of tempering or electricity theft
  • Energy Audit
  • Measurement of other important electric components like Voltage, Current, Power Factor, MDI (Maximum Demand Indicator) etc.

The explanations of these objectives require another complete article.

Here, in this article let’s just stick with the basics of energy meters.

Working principle of Energy Meters:

There are many types of energy meters having different working principle. Basic working principle of all energy meters are same except disk type energy meter. As disk type energy meters are obsolete there is no need to discuss them here.  To understand the basics , Simple Digital Energy Meters is the best option because all the other meters are merely an upgraded form of them.

Study an article on how to read Electricity Meters

These are the essential blocks of a basic LCD digital meter:

Working Principle of Energy Meters
Figure 3: Working Principle of Energy Meters

Power supply circuit:

The goal of this circuit is to give 5 volts to the whole system. Power supply can be provided to the system through any of the ways written in this article. To Energize LCD and EEPROM without even power supply, a battery is an only option. For that purpose, a non-rechargeable Lithium battery should install inside to energize it for at least 4-5 years.

There is a reason why they are using non-rechargeable battery. Study an article on it here.

Current Measuring Circuit:

There are many ways to measure current and for this purpose various kinds of sensors are available in the market. To measure current, sensor should be applied in series of the Live wire so that whole current can be passed through sensor. Current transformer is the best option in this case due to its economical price and efficiency.

Study complete article on how to make current measuring circuit here.

Voltage Measuring Circuit:

There are two main methods to measure voltage. One is through the voltage divider and the other through potential transformer. When voltage is too high like more than 500 volts then a potential transformer should be used to isolate the sensitive circuit from high voltage. But in case of 220 volts a voltage divider circuit is better option. Many Energy Meter manufacturers use this voltage divider method to make voltage measuring circuit.

A complete guide on how to measure voltage without (PT) potential transformer can be studied here.

Liquid Crystal Display:

A LCD is the face of Energy Meter. It gives reading to the meter readers. Any small and cheap LCD can serve the purpose here.

Want to know how to read your Energy Meter? Click Here

Normally following things are required to display on the LCD of single phase energy meters:

  • Previous Month KWh consumption
  • Present month KWh consumption
  • Total kWh consumption time of manufacturing
  • Previous month MDI (kW)
  • Present Month MDI (kW)
  • MDI Reset Number
  • Meter serial Number

Study an article on how to interface LCD with micro controller here.

EEPROM (Electrically Erasable Programable Read Only Memory):

EEPROM is another important part of Energy Meters. It stores MDI and total kWH consumption for every 30 minutes. So that retrieval of consumed units could be possible in case of any discrepancy.


You can call micro-controller as Brain of the Energy Meter. Meter manufacturing company can use any micro-controller like PIC, Atmel AVR or ARM solely depends on their constraints. Moreover specified micro-controllers “specifically designed for Energy Measurements” are also present in Market. The purpose of the micro-controller here is to collects analog values from current and voltage circuit and then convert it into digital values through ADC. After conversion, a multiplication of digital values of current and voltage done by micro-controller to get the value of power consumption. This value of power then add into the energy register with previous values. In the end, it displays all the values on the LCD and store it into the EEPROM as well.

Study a complete article on how to design a Smart Energy Meter.

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