Page 304 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

It’s inbuilt around a current transformer and other active devices (voltage comparator), which converts the sensed
current to voltage for processing. The output from both sensors is then fed into a signal (voltage) conditioner
which ensures matched voltage (or) signal level to the control circuit containing multiplexer. It enables sequential
switching of both signal to the analogue input of the Peripheral Interface Controller (PIC).
The control circuit centred on a PIC integrated circuit. It contains ten bit analogue to digital converter (ADC),
flexible to program and good for peripheral interfacing.
The ADC converts the analogue signals to its digital equivalent, both signals from the voltage and current sensors
are then multiplied by the means of embedded software in the PIC.
The error correction is taken as the offset correction by determining the value of the input quality in the short
circuited input and storing this value in the memory for use as the correction value device calibration.

The PIC is programmed in ‘C’ language. It stimulates to use the received data to calculate power consumption
per hour, as well as the expected charges. These are displayed on the liquid crystal display (LCD) attached to
the circuit.

Fig 2 shows the image of a digital energy meter.
Advantages
DIGITAL electronic meters are much more accurate than electromechanical meters. There are no moving parts
and, hence, mechanical defects like friction are absent

Fig 2

3-phase energy meter

Objectives: At the end of this lesson you shall be able to:
• list the various types of 3-phase energy meters
• describe the construction and working of a 3-phase 3-wire induction type energy meter
• describe the construction and working of a 3-phase 4-wire induction type energy meter
• state the application of a 3-phase 3-wire and 3-phase 4-wire energy meter.

3-phase energy meters: Even though different types of energy meters are available, the induction type energy
meter is most commonly used because it is simple in construction, less in cost and requires less maintenance.
The function of a 3-phase energy meter is similar to that of a single phase energy meter.
Types of 3-phase energy meters

There are two types of 3-phase energy meters mainly.
• Three phase 3-wire energy meters (3-phase 2- element energy meter)
• Three phase 4-wire energy meters (3-phase 3- element energy meter)

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CITS : Power - Electrician & Wireman - Lesson 50-53 CITS : Power - Electrician & Wireman - Lesson 50-53