An electric meter is an essential device that consumes energy allocated by businesses. It can systematically price the energy consumed by a single consumer because it can measure the electrical energy consumed by houses, businesses or electric equipment. They are usually calibrated in billing units. The most common unit is kilowatt-hour, which is equal to the energy consumed by a kilowatt load in one hour, which is 3,600,000 joules.
Some electric meters only measure the length of time that the charge flows, but not the magnitude of voltage or current. These are only suitable for constant load applications. Both types are unlikely to be used today. In addition to metering based on the energy used, other types of metering can also be used. In the early days of electrification, an electric meter (called an ampere hour meter) was used to measure the amount of charge (coulomb) used. These depend on the power supply voltage being kept constant to accurately measure energy usage, which is unlikely for most power supplies.
Generally, the working method of an electric meter is to continuously measure the instantaneous voltage (volt) and current (ampere), and then find the product of them to get the instantaneous electric power (watt), and then integrate the time to get the energy used (joule, kilowatt) Time waiting). Meters used for small services (such as small residential customers) can be directly connected in series between the source and the customer. For larger loads (loads of more than 200 amperes), current transformers are required, so the meter can be placed out of line with the service wires . Instruments are divided into two basic categories: electromechanical and electronic. This article stays on the electronic instrument (ie digital instrument)
Traditional electromechanical instrument. It has a rotating disk and a mechanical counter display. This type of meter works by calculating the rotational speed of a metal disk, which is proportional to the power drawn through the main fuse box. A nearby coil rotates the disk by inducing eddy currents and a force proportional to the instantaneous current and voltage. The permanent magnet exerts a damping force on the disc, and stops rotating after a power failure. This type of instrument has many limitations that make it completely irrelevant to use in a smart energy active environment, including but not limited to accuracy.
There are many error correction methods in digital meters, which are usually based on known A/D converter error correction methods. Most of these methods use software calibration based on the calibration process. In a digital meter, the percentage error may be as low as 0.01%, while in an analog meter, the error usually exceeds 0.05%.
Secondly, the orientation problems associated with electromechanical energy meters are not a problem at all in digital energy meters. Therefore, installation becomes easier. Third, the user-friendly display in the digital meter makes it very easy to read power. The fourth and most serious setback of the electromechanical energy meter is its non-interface function with external equipment. This setback is very serious in the application of smart grid technology.
Electronic meters use highly integrated components or other custom integrated circuits to measure energy. These devices digitize the instantaneous voltage and current through a high-resolution sigma-delta ADC, and calculate the product of the voltage and current to obtain the instantaneous power in watts. Over time, integrals produce the energy used, usually in kilowatt hours (kWh). The design technology of digital electric meters is influenced by three main factors: required equipment cost, efficiency and overall size. Although the cost is affected by the user's overall affordability, the efficiency and size must strictly meet the standards.
Block diagram of digital meter. Here, two basic sensors are used. These are voltage and current sensors. The voltage sensor built around the step-down element and the voltage divider network can sense the phase voltage and the load voltage. The second sensor is a current sensor. This can sense the current drawn by the load at any point in time. It is built around current transformers and other active devices (such as voltage comparators) that convert the sensed current into voltage for processing. Then feed the output of the two sensors into a signal (or voltage) regulator to ensure the voltage or signal level that matches the control circuit. It also contains a signal multiplexer that can convert The two signals are sequentially switched to the analog input (PIC) of the peripheral interface controller. The control circuit is centered on the PIC integrated circuit. The PIC was chosen because it contains a ten-bit analog-to-digital converter (ADC), programming is very flexible, and very suitable for peripheral interfaces.
The ADC converts the analog signal to its digital equivalent signal. Then, the two signals of the voltage and current sensors are multiplied by the embedded software in the PIC. Here, by determining the value of the input quality of the input short-circuit and storing the value in the memory to be used as a correction value device calibration, error correction is used as offset correction. PIC is programmed in C language. In this way, in addition to the multiplier circuit it simulates, it can also use the received data to calculate the hourly power consumption and expected cost. These are displayed on a liquid crystal display connected to the circuit.
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