MCP3909-I/SS Microchip Technology, MCP3909-I/SS Datasheet - Page 41

• Manufacturer Part Number: MCP3909-I/SS
• Description: IC POWER METERING-1 PHASE 24SSOP
• Manufacturer: Microchip Technology

Specifications of MCP3909-I/SS

• Package / Case: 24-SSOP (0.200", 5.30mm Width)
• Input Impedance: 390 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.85V
• Current - Supply: 2.3mA
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Meter Type: Single Phase
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Supply Voltage Range: 4.5V To 5.5V
• Digital Ic Case Style: SSOP
• No. Of Pins: 24
• Interface Type: Serial, SPI
• Supply Voltage Max: 5.5V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: MCP3909EV-MCU16 - EVALUATION BOARD FOR MCP3909MCP3909RD-3PH1 - REF DESIGN MCP3909 3PH ENGY MTR
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

4.4
© 2009 Microchip Technology Inc.
PHASE LAG CALIBRATION
The phase lag calibration function is implemented by the upper computer by sending
the proper commands via the UART. When calibrating phase lag, error from the
calibration equipment and channel information to be adjusted are sent to the dsPIC33F
energy meter. When the front-end receives the command, it calls this module. The flow
is as follows:
1. Determine the phase to be calibrated according to parameters received.
2. Calculate new phase lag calibration coef. according to the error value received
3. Store the coefficient after correction into the EEPROM.
This meter design supports single, two, and five point calibration for phase lag error
correction.
The purpose of phase lag calibration is to eliminate the impact of phase lag introduced
by the current transformer (CT), and voltage transformer (PT) over the power measure-
ment range.
The voltage transformer usually has a constant load, thereby introducing a phase lag
that varies insignificantly. The dynamic range of current is larger, and under different
current loads, phase lags caused by CT vary greatly. In order to meet the requirements
of measurement accuracy in the entire range, it is usually necessary to segment the
phase lag and calibrate.
In this design, current is partitioned into 5 regions.
TABLE 4-1:
The partition limit for the current region can be modified in the header file of the
program. If accuracy is not critical, single-point calibration and two-point calibration can
be used to improve the efficiency of meter calibration.
Single, Two, or Five Point Calibration
Single-, two- or five-point calibration method can be configured by modifying the
header file. When using the single-point calibration, the phase lag compensation
values of all regions are the same; When using two-point calibration, the compensation
values of region 1 and 2 (0-0.075 I
compensation values for region 3, 4 and 5 (0.2 I
4.0 I
and the measured value.
B
) are the same.
Region
1
2
3
4
5
CURRENT REGIONS FOR PHASE CALIBRATION
B
, 0.075 I
B
- 0.2 I
Current Range
0.075 I
0.2 I
0.75 I
1.5 I
B
0 - 0.075 I
- 0.75 I
B
B
B
) are the same, and the phase lag
Meter Calibration
B
- 0.75 I
B
- 4.0 I
-1.5 I
- 0.2 I
B
B
, 0.75 I
B
B
B
B
B
- 1.5 I
DS51723A-page 41
B
, 1.5 I
B
-