 WHAT IS ELECTRICAL ENERGY ?

Kinetic Energy of the generator or Chemical Energy of the cell is converted into Electrical Energy which flows through the circuit and is converted back into Light, Heat, and kinetic Energy.

Energy flows from source to load.

ELECTRICAL ENERGY IN AN AC CIRCUIT

p(t) = v(t)*i(t)

Total Energy (E) is equal to integral of p(t) over time

E = p(t)dt = v*i*t = joules = watts-sec

WHAT IS ELECTRICAL POWER?

Electrical Power is the rate of flow of Electrical Energy in a circuit. The unit of power is the watt and is defined as joules per second. Therefore we can see that power is a rate expression

Power is equal to the rate of flow of Electrical Energy

P = dE/dt = V*I

DATA ACQUISITION : ANALOG FRONT END IC ADE7753

Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer .One of the most annoying challenges for designers of general-purpose metering systems is the design of an analog front-end for input signals that range from tens of Milli volts to hundreds of volts while spanning a wide frequency range. Several of the challenges can be solved by carefully selecting the amplifier used to drive the ADC. Today’s ADCs have phenomenal signal-to-noise ratio (SNR) and resolution. By understanding the relationship between amplifier specifications and converter requirements, you can optimize resolution and throughput of the data acquisition system.

One of the best manufacturers of Analog Front End IC is Analog Devices. On that note i would like to introduce a product of them with high reliability in data acquisition metering solution.The ADE7753 features proprietary ADCs and DSP for high accuracy over large variations in environmental conditions and time. The ADE7753 incorporates two second-order 16-bit ∑-Δ ADCs, a digital integrator (on CH1), reference circuitry, temperature sensor, and all the signal processing required to perform active, reactive, and apparent energy measurements, line-voltage period measurement, and RMS calculation on the voltage and current. The selectable on-chip digital integrator provides direct interface to di/dt current sensors such as Rogowski coils, eliminating the need for an external analog integrator and resulting in excellent long-term stability and precise phase matching between the current and voltage channels. The ADE7753 provides a serial interface with the micro-controller in this case we are using to read data, and a pulse output frequency (CF), which is proportional to the active power. Various system calibration features, i.e., channel offset correction, phase calibration, and power calibration, ensure high accuracy. The part also detects short duration low or high voltage variations.The positive-only accumulation mode gives the option to accumulate energy only when positive power is detected. An internal no-load threshold ensures that the part does not exhibit any creep when there is no load. The zero-crossing output (ZX) produces a pulse that is synchronized to the zero-crossing point of the line voltage. This signal is used internally in the line cycle active and apparent energy accumulation modes, which enables faster calibration. The interrupt status register indicates the nature of the interrupt, and the interrupt enable register controls which event produces an output on the IRQ pin, an open-drain, active low logic output. The ADE7753 is available in a 20-lead SSOP package.

THEORY OF OPERATION AFE IC ‘ADE7753’

• Analog Signals on Channel 1 and Channel 2 are digitized by the two ADCs.

• These signals (Current and Voltage) are multiplied in a digital multiplier.

• Multiplication generates an INSTANTANEOUS POWER SIGNAL.

• The REAL POWER is extracted from the INSTANTANEOUS POWER by a Low Pass Filter.

• REAL POWER is converted to a FREQUENCY by the DIGITAL-TO-FREQUENCY Converters.