Electrical energy meters having factory set calibration circuits therein and methods of calibrating same

An electrical energy meter, comprising:

• a meter housing;
• a printed circuit board in said housing;
• means, on said printed circuit board, for metering a quantity of electrical energy transferred from a line to a load during an energy measurement time interval, said metering means comprising:
• means for sensing a line voltage and a line current transferred to the load during the energy measurement time interval;
• means, connected to said sensing means, for generating an energy signal based on the sensed line voltage and the sensed line current;
• and
• means, connected to said generating means, for calibrating said generating means so that the energy signal accurately reflects the quantity of electrical energy transferred to the load during the energy measurement time interval, said calibrating means comprising a power factor calibration circuit containing at least one pair of antiparallel-connected diodes and a gain calibration circuit having a resistor ladder therein containing at least three resistors of different resistance, and wherein each resistor is fixedly attached to said printed circuit board and includes a resistive portion and exposed dual lead portions which can be cut so that respective resistive portions can be readily disconnected from the resistor ladder to facilitate calibration of said generating means;
• means, on said printed circuit board and responsive to said metering means, for registering the metered quantity of electrical energy transferred to the load during the energy measurement time interval;
• and
• means, electrically connected to said registering means, for displaying the quantity of electrical energy transferred to the load during the energy measurement time interval.

A method of calibrating an electrical energy meter of the type containing a meter integrated circuit for metering a quantity of electrical energy transferred from a line to a load during an energy measurement time interval, first and second pairs of antiparallel-connected diodes for adjusting the non-unity power factor response of the meter integrated circuit, a resistor ladder for adjusting the full load gain of the meter integrated circuit, and a register integrated circuit for registering the metered quantity of electrical energy, said meter calibrating method comprising the steps of:

• measuring a first known quantity of electrical energy to thereby obtain a first measured quantity of electrical energy which depends on a first resistance of the resistor ladder;
• determining a difference between the first measured quantity and the first known quantity;
• determining a second resistance of the resistor ladder such that the first measured quantity will equal the first known quantity;
• disconnecting at least one resistor from the resistor ladder to obtain the second resistance;
• measuring a second known quantity of electrical energy at non-unity power factor to thereby obtain a second measured quantity of electrical energy;
• determining a difference between the second measured quantity and the second known quantity;
• and
• disconnecting at least one of the first and second pairs of antiparallel-connected diodes so that the second measured quantity will equal the second known quantity.