Datasheet AD71056 (Analog Devices) - 6

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AD71056 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 AD71056 is defined by the following formula: analog inputs to the ADCs. However, the HPF in Channel V1 Energy Registered by AD71056 − True Energy eliminates the offset in the circuitry. Therefore, the power %Error = × % 100 calculation is not affected by this offset. True Energy
Frequency Output Error (CF)
The frequency output error of the AD71056 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 correction frequency is obtained from the AD71056 transfer function. See network is also placed in Channel V1. The phase correction Figure 14 for a typical distribution of part-to-part variation of network matches the phase to within 0.1° over a range of 45 Hz CF frequency. to 65 Hz, and 0.2° over a range 40 Hz to 1 kHz (see Figure 23 and Figure 24).
Gain Error
The gain error of the AD71056 is defined as the difference
Power Supply Rejection (PSR)
between the measured output of the ADCs (minus the offset) This quantifies the AD71056 measurement error as a and the ideal output of the ADCs. The difference is expressed percentage of reading when the power supplies are varied. as a percentage of the ideal output of the ADCs. For the ac PSR measurement, a reading at nominal supplies (5 V) is taken. A 200 mV rms/100 Hz signal is then introduced
Oscillator Frequency Tolerance
onto the supplies and a second reading is obtained under the The oscillator frequency tolerance of the AD71056 is defined as same input signal levels. Any error introduced is expressed as a the part-to-part frequency variation in terms of percentage percentage of reading—see the Measurement Error definition. at room temperature (25°C). It is measured by taking the difference between the measured oscillator frequency and the For the dc PSR measurement, a reading at nominal supplies nominal frequency as defined in the Specifications section. (5 V) is taken. The supplies are then varied 5% and a second reading is obtained with the same input signal levels. Any error
Oscillator Frequency Stability
introduced is, again, expressed as a percentage of reading. Oscillator frequency stability is defined as the frequency variation in terms of the parts-per-million drift over the operating temperature range. In a metering application, the temperature 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 TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS TIMING CHARACTERISTICS Timing Diagram ABSOLUTE MAXIMUM RATINGS ESD CAUTION TERMINOLOGY PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION POWER FACTOR CONSIDERATIONS NONSINUSOIDAL VOLTAGE AND CURRENT APPLICATIONS 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 Frequency Output CF SELECTING A FREQUENCY FOR AN ENERGY METER APPLICATION Frequency Outputs NO LOAD THRESHOLD NEGATIVE POWER INFORMATION OUTLINE DIMENSIONS ORDERING GUIDE