MCP3909RD-3PH3 Microchip Technology, MCP3909RD-3PH3 Datasheet - Page 97

• Manufacturer Part Number: MCP3909RD-3PH3
• Description: REF DESIGN FOR MCP3909 W/18F2520
• Manufacturer: Microchip Technology

Specifications of MCP3909RD-3PH3

• Main Purpose: Power Management, Energy/Power Meter
• Utilized Ic / Part: MCP3909, PIC18F2520, PIC18F4550
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

C.15 RATIO ERROR COMPENSATION
© 2009 Microchip Technology Inc.
As non-linearity and inconsistency exist in the sampling circuit (including CT and
back-end shunt resistors) and the ADC circuit, it is necessary to compensate for ratio
error to the system. Figure C-9 is the transfer link of the voltage and current channels.
The compensation for ratio error is quite simple. It compares the measured value
against the actual input value under certain input conditions and obtains a correction
coefficient.
EQUATION C-65:
FIGURE C-9:
Since current has a large dynamic range, for a meter which requires high accuracy
(0.2s and 0.5s), the multi-point calibration method is needed to meet input requirement
for full range. The MCP3909 device's current channel includes an adjustable gain
amplifier. The ratio error must be recalibrated for different amplification, but only needs
to be calibrated once under the same amplification conditions.
Voltage
Current
Correction coefficient
Input
Input
Error Caused By Sampling Circuit And ADC.
Sampling resistor
Voltage primary
R0
=
Coefficient before correction
Power Calculation Theory
2000:1
CT
1:1
CT
Voltage secondary
Current secondary
Sampling resistor
Sampling resistor
×
Calibration Value
------------------------------------------ -
Measured Value
ADC
ADC
DS51723A-page 97