Single phase split energy prepayment electronic meters currently being deployed in Nigeria by the power holding company of Nigeria (PHCN) comes in two units. One of this units is called the monitor unit. The monitor unit is the smaller of the two meter units installed in the consumer’s premises.

The monitor unit provides the user interface to enable the consumer to interact with the meter.

Here are some of its features:

nine digit LCD display

It has a built-in nine digits LCD display that display some meter information to the consumer. Information that can be read from the monitor unit includes:

Available credit: this is the default information displayed. This tells you how much energy credit you have left (in kilowatt-hour kWh). This value however is not the value of money in your meter. To calculate the currency value in your meter, multiply this value by the energy rate. In Nigeria this is N4.00/kWh.

For example if your meter displays 192.35 your available energy credit in Naira is N769.40.

Cumulative energy credit: you can also find out the total energy you have consumed since you installed prepayment meter. This value is in kWh. This can help you manage your future energy spending.

Meter constant: this value is fixed by energy meter manufacturer.

Meter version: this is also fixed at manufacture and informs you of the version of your meter.

Meter number: this is a number unique to your meter and set by manufacturer.

credit loading status: when loading credit monitor unit displays a series of hyphens on the display (——–). This is a signal that the credit on your customer’s smartcard is being transferred through monitor unit to main energy-metering unit. Once this is complete, your updated available credit level will be displayed.

Errors may occur when loading your energy credit.

Error status: monitor unit displays error information if any error occurs during operation. This error messages comes inform of error codes. For details on interpretation of these error messages consult your energy meter’s user manual.

12 digits keypad

The monitor unit has a built-in 12 digits keypad. This consists of 10 digits (0 to 9), a delete key and a composite navigational and enter key. The keypad is enclosed and is only visible when the card door is open.

The composite navigational and enter key is used to navigate through meter display. By pressing this key, you can view meter information like cumulative energy consumption, meter constant, meter version, and meter number. A new value will be displayed each time you press enter key.

The number and delete keys are used for loading recharge pin into the meter. For now recharge pins are not used in Nigeria.

Smartcard system

The monitor unit incorporates a smartcard system, which is used to load credit into the energy meter.

tri-colour LED credit level indicator

The monitor unit includes tri-colour Light Emitting Diode (LED) indicator. Once you load credit into your energy-metering unit the LED will be green, indicating that you have sufficient credit. When your credit level drops between 30% and 20% of last credit loaded into the meter, LED turns yellow.

When available credit falls between 20% and 10% of your last credit level, LED turns red. The LED starts flashing (glowing on and off) once credit level falls below 10% of your last credit purchase. This is a good time to buy more energy credit. If you fail to do this, your energy meter will trip off and power supply will stop when your available credit falls to zero.

four terminals communications port

The monitor unit is connected to the energy-metering unit via a communications port. This consists of four terminals. Two of these terminals are for power supply while the other two is for communication between energy-metering unit and monitor unit.

The monitor unit is powered by the metering unit via this communication cable and connects the two together.

The two units also interact together via their respective communications port. For example when you insert your smart card into the monitor unit, information downloaded at your last vend is transferred to the metering unit. This includes the energy sum bought, tariff rates, class of tariff and so on.

The metering unit uses the communication port to regularly update the credit level records on the monitor unit’s LCD display.

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