Datasheet ADE7768 (Analog Devices) - 6

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ADE7768 TERMINOLOGY Measurement Error ADC Offset Error
The error associated with the energy measurement made by the This refers to the small dc signal (offset) associated with the ADE7768 is defined by the following formula: analog inputs to the ADCs. However, the HPF in Channel V1 eliminates the offset in the circuitry. Therefore, the power Energy Registered by ADE7768 −True Energy %Error = × % 100 calculation is not affected by this offset. True Energy
Frequency Output Error (CF)
The frequency output error of the ADE7768 is defined as the
Phase Error Between Channels
difference between the measured output frequency (minus the The high-pass filter (HPF) in the current channel (Channel V1) offset) and the ideal output frequency. The difference is has a phase-lead response. To offset this phase response and expressed as a percentage of the ideal frequency. The ideal equalize the phase response between channels, a phase- frequency is obtained from the ADE7768 transfer function. correction network is also placed in Channel V1. The phase- correction network matches the phase to within 0.1° over a
Gain Error
range of 45 Hz to 65 Hz, and 0.2° over a range 40 Hz to 1 kHz The gain error of the ADE7768 is defined as the difference (see Figure 24 and Figure 25). between the measured output of the ADCs (minus the offset) and the ideal output of the ADCs. The difference is expressed
Power Supply Rejection (PSR)
as a percentage of the ideal of the ADCs. This quantifies the ADE7768 measurement error as a percentage of reading when the power supplies are varied.
Oscillator Frequency Tolerance
The oscillator frequency tolerance of the ADE7768 is defined as For the ac PSR measurement, a reading at nominal supplies the part-to-part frequency variation in terms of percentage at (5 V) is taken. A 200 mV rms/100 Hz signal is then introduced room temperature (25°C). It is measured by taking the differ- onto the supplies and a second reading is obtained under the ence between the measured oscillator frequency and the same input signal levels. Any error introduced is expressed as a nominal frequency defined in the Specifications section. percentage of reading—see the Measurement Error definition.
Oscillator Frequency Stability
For the dc PSR measurement, a reading at nominal supplies Oscillator frequency stability is defined as frequency variation (5 V) is taken. The supplies are then varied 5% and a second in terms of the parts-per-million drift over the operating reading is obtained with the same input signal levels. Any error temperature range. In a metering application, the temperature introduced is again expressed as a percentage of the reading. range is −40°C to +85°C. Oscillator frequency stability is measured by taking the difference between the measured oscillator frequency at −40°C and +85°C and the measured oscillator frequency at +25°C. Rev. A | Page 6 of 20 Document Outline FEATURES GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM SPECIFICATIONS TIMING CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS ESD CAUTION TERMINOLOGY PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS FUNCTIONAL DESCRIPTION THEORY OF OPERATION Power Factor Considerations Nonsinusoidal Voltage and Current ANALOG INPUTS Channel V1 (Current Channel) Channel V2 (Voltage Channel) Typical Connection Diagrams POWER SUPPLY MONITOR HPF and Offset Effects Digital-to-Frequency Conversion Connecting to a Microcontroller for Energy Measurement Power Measurement Considerations INTERNAL OSCILLATOR (OSC) TRANSFER FUNCTION Frequency Outputs F1 and F2 Example Frequency Output CF SELECTING A FREQUENCY FOR AN ENERGY METER APPLICATION Frequency Outputs NO-LOAD THRESHOLD NEGATIVE POWER INFORMATION EVALUATION BOARD AND REFERENCE DESIGN BOARD OUTLINE DIMENSIONS ORDERING GUIDE