Wednesday, August 27, 2008

Current Reversal Tampering

The aluminium rotor disc present in the electricity meter runs in the clockwise direction as long as the neutral and phase connections are connected properly to it. But if these two wires are reversed, the meter starts to malfunction thereby rotating in the reverse direction ther by leading to reduction in meter reading. Hence to monitor the proper rotation of aluminium rotor disc and to avoid the current reversal tampering, a pair of LED and Photodiode duo ( LED 1 and LED 2 ) are placed above and below the aluminium rotor disc as shown in the figure above.

To let the light from LED fall on the photodiode, a slot is cut on the aluminium rotor disc. When the disc rotates in clockwise direction, light from LED1 falls first on the Photodiode 1 followed by the other, LED2 light falling on Photodiode 2. The output of the photodiodes are given to individual microcontroller ports with the help of a pull up circuit. As long as the sequence of LED1 and LED2 output enters the microcontroller, there is no tampering. If the order of photodiode output to the microcontroller is reversed, LED2 output reaching the microcontroller first followed by LED1 output, then there is the possibility of Current reversal tampering being attempted.

When the ports A and B respectively for Photodiode 1 and Photodiode 2 outputs are detected in order, two LEDs placed outside the electricity meter glow in order to indicate the perfect working of the electricity meter. When the ports are detected in reverse order, the LEDs glow in the reverse order as well, so as to indicate malfunctioning.

As the rotor disc rotates in the opposite direction, the tampering information is sent to the micro controller. When micro controller receives the signals, it transfers it to the LCD and the GSM modem. So an information about the tampering that has occurred is displayed in the LCD, as well as sent to the electricity board through the GSM modem.

Thus the tampering of the electricity meter using the current reversal technique is detected and intimated to the electricity board for further action.

Please see my previous post on the project 'Embedded Based Power Tampering Detection and Automatic Meter Reading System Using GSM' for more details.

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