TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT AN_6511_020 NOVEMBER 2005 71M6511 Calibration of a Single Phase Meter with Shunt and CT Single-phase residential meters use a shunt resistor combined with a current transformer (CT) in order to enable tamper-detection. This application note describes the calibration procedure and the method to compute billing values for single phase metering. The second part of this application note describes common methods of tampering and ways to detect tampering. Rev. 2.2 1 TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT Block Diagram: 6511 IA L6 J3 R110 TP21 R14 IA IA_IN FERRITE GND 0 IA 750 V3P3 HDR2 U1 HDR3 1 2 3 L7 SHUNT A1 C1 AC2 AC1 C2 A2 6 5 4 C8 1nF D8 UCLAMP3301D BAV99DW V3P3 FERRITE J16 GND IB L4 T1 R111 TP22 R104 IB IB_IN FERRITE GND 0 IB 750 HDR2 U6 HDR3 R106 3.4 1 2 3 R107 3.4 L5 A1 C1 AC2 AC1 C2 A2 6 5 4 C29 1nF BAV99DW V3P3 FERRITE L3 JP17 FERRITE VA V3P3 V3P3J2 HDR2 L1 FERRITE JP16 GND HDR3 V3P3_JUMPER L2 LOAD R18 R17 R16 R15 2M 274K 270K 700 TP4 V3P3 V3P3 GND FERRITE R32 750 HDR2 C9 220pF VA V3P3J2 J9 V3P3_JUMPER 1 SPADE C32 30nF GND RV1 510V L8 R118 J4 8.06K + C1 D3 1N4736A + C2 10uF TL431 8 + C4 33uF 6.8V, 1W 0.47uF, 1000Vdc C6 R6 D4 R7 100, 2W 1N4148 180 25.5K R26 GND 1 SPADE C5 0.1uF 6 R8 1 1 2200uF, 16V 2 C14 30nF 1 LINE FERRITE 10, 2W 0 JP1 HDR2 NEUTRAL C38 10nF, 250VDC Note: The reference designators in this Block Diagram apply to the 2-layer 6511 Demo Board. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT Definitions and Procedure: 1. Set the meter equation field of the configuration RAM for EQU to zero using the command: RI00 = 10 // EQU = 0; CE_EN =1; TMUX = 0; 2. The shunt resistor is connected to Phase 0 (channel A), and the CT is connected to Phase 1 (channel B). The calibration procedure described in next section is applicable to this sensor arrangement. But one can easily modify this procedure to the desired CT/Shunt combinations. 3. For the sake of calculation, individual WRATE parameters for Pulse generation, i.e. WRATE_SHUNT and WRATE_CT will be used. 4. It is also necessary to compute and estimate IMAX_SHUNT and IMAX_CT parameters for meter billing purposes. 5. Using IMAX_SHUNT and VMAX, the energy calculations for channel A should be performed. 6. Using IMAX_CT and VMAX, the energy calculations for channel B should be performed. 7. The LSB values for measurements for W0SUM / W1SUM/ VAR0SUM/ VAR1SUM/ I0SQSUM/ I1SQSUM/ V0SQSUM should be modified to compute the correct energy values. That is, IMAX_SHUNT and IMAX_CT should be applied separately to individual channels based on the sensor connections. 8. Before starting a calibration it should be ensured that all coefficients are in their default state, i.e. CAL_IA (0x08), CAL_VA (0x09), CAL_IB (0x0a) must be 16384. PHADJ_A (0x0e) and PHADJ_B (0x0f) should be zero. * (0x0p) represents the CE register address. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT Calibrating for Shunt Resistor (Channel A): 1. Estimate IMAX for the shunt resistor (IMAX_SHUNT). This can be done by using the following formula: IMAX_SHUNT = ViMAX/RSHUNT ---This adjusted IMAX value is stored as IMAX_SHUNT at the MPU address location that can be updated using the command )A= IMAX_SHUNT of the Demo Code supplied by TERIDIAN. ---The ViMAX value is the maximum analog input voltage for the channel, typically 176mV (RMS). 2. Apply VMAX = 600V (RMS) for the 6511 Demo Board if the resistor divider for VA has not been changed. 3. WRATE_SHUNT is computed based on IMAX_SHUNT and VMAX. 4. Update the CE WRATE register (0x2D) with WRATE_SHUNT. 5. Test for accuracy at 15A, 240V at phase angle 0, phase angle 60 and at phase angle –60 degrees. 6. Apply the error values to the supplied spreadsheet (revision 2.0 or later) and determine the calibration coefficients for channel A, i.e. CAL_IA, CAL_VA, and PHADJ_A. 7. Update the CE registers 0x08, 0x09 and 0x0E of the compute engine with the calibration coefficients obtained from the spreadsheet, using the commands ]8=CAL_IA, ]9=CALVA, and ]E=PHADJ_A. 8. Retest for accuracy at several currents and phase angles. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT Calibration for CT (Channel B): 1. Assign/compute IMAX for the CT channel (IMAX_CT), based on the CT turns ratio N and the termination resistor value RTermination using the formula: IMAX_CT = 176mV* N/ (RTermination) This IMAX value is stored as IMAX_CT. 2. Compute WRATE_CT based on the IMAX_CT and VMAX. 3. Update the CE WRATE variable with WRATE_CT. 4. Enter the command >)7=2; Configure W1SUM as external pulse source since the CT is connected to Channel 1 for VA*IB. 5. Test for accuracy at 15A, 240V at phase angle 0, phase angle 60 and at phase angle –60. 6. Apply these values to the supplied spreadsheet (revision 2.0 or later) and derive the calibration coefficients for PHADJ_B. 7. Update only the field ]f of the CE registers with the value for PHADJ_B. 8. CAL_IB should be adjusted for the total error found in the tests using the formula CAL_IB = 16384 * (1 - error/100) since CAL_IA and CAL_VA are already fixed by the sensor used on Phase A. That is, if the chip reports an error of -2.5%, CAL_IB should be adjusted for a value of (16384 * (1 - (-2.5/100)). 9. Since CAL_VA is already adjusted, this register should not be updated. 10. Retest for accuracy at several currents and phase angles. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT Tamper Detection Using CT and Shunt. Tampering has become a common practice for reducing electricity consumption in single-phase metering. To prevent tampering, meter manufacturers opted for solid-state electricity meters. Teridian’s 71M6511/6511H metering chip provides solutions to the meter manufacturers for tamper detection. This part of the application note describes the details of tamper detection. 71M6511 is a single phase metering chip with provision for two current sensor inputs and one voltage input. Under normal operation the meter designed for tamper detection contains two current sensors and one voltage sensing input through the resistor dividers. The following sensor combinations can be used for tamper detection using the 71M6511 chip. Combination 1 2 3 IA_Input Current_Shunt Current_Transformer Current Transformer IB_Input Current_Transformer Current_Shunt Current Transformer Please note that the option involving two current shunts is not allowed, since the shorting of live and neutral wires can occur with this combination. The metering Equation for supporting the above above combination for tampering should be ‘0’ . That is, the Compute Engine provides two output energy registers W0SUM_X ( VA * IA) and W1SUM_X (VA * IB) using metering Equation ‘0’ that can be used for tampering. The MPU firmware can easily be implemented for Tamper detection using the available Energy Registers. Also please note that the VAR0SUM_X and VAR1SUM_X registers are also available if one wishes to implement tampering using VARhours. Under normal operation the single-phase meter can be used for tamper detection with one of the above combination of sensors. Following is a diagram showing a single-phase meter connected as per combination 1 (from the above table). The meter equations are the same for all combinations provided in the above table. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT LIVE LOAD NEUTRAL (-)Ia=(-)Ib Figure 1: Single phase meter with two sensors under normal operation (no tampering) The following diagrams show some of the possible tamper methods that can be prevented using the 71M6511/6511H with two current sensors. All diagrams provide the current measured for easy understanding of Tamper detection. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT NEUTRAL LIVE Ia=0 ETH (+)Ib=IETH Figure 2: Tamper method #1, L and N swapped, load to GND. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT NEUTRAL LIVE Ipart LOAD Ieth ETH (+)Ia=Ipart (+)Ib=Ieth+ Ipart Ieth=Ib-Ia Figure 3: Tamper method #2, L and N swapped, load partially connected to GND. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT NEUTRAL LIVE LOAD Ieth ETH Ia=0 (-)Ib=Ieth Figure 4: Tamper method #3, L and N swapped, l/O swapped, LOAD connected to GND. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT Ipart NEUTRAL LIVE LOAD Ieth ETH (-)Ia=Ipart (-)Ib=Ieth+Ipart Ieth=Ib-Ia Figure 5: Tamper method #4, L and N swapped, l/O swapped, LOAD partially connected to GND. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT I_Ioad LIVE LOAD NEUTRAL I_Ioad Ia=0 (-)Ib=I_load Figure 6: Tamper method #5, Lin and Lout externally shorted (Lin=Lout). © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT I_Ioad LIVE LOAD NEUTRAL I_Ioad Ia=0 (-)Ib=I_load Figure 7: Tamper method #6, Lin and Lout externally bypassed (Lin=Lout). © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT I_Ioad NEUTRAL LOAD LIVE I_Ioad Ia=0 (+)Ib=I_load Figure 8: Tamper method #7, L and N swapped, Lin and Lout externally bypassed (Lin=Lout). © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT NEUTRAL LOAD LIVE I_Ioad (-)Ia=(+)Ib=I_load Figure 9: Tamper method #8, L&N swapped. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT NEUTRAL LIVE LOAD (-)Ia=(-)Ib Figure 10: Tamper method #9, L and N swapped, I/O swapped © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT LIVE NEUTRAL LOAD (+)Ia=(+)Ib=I_load Figure 11: Tamper method #10, I/O swapped. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT LOAD LIVE I_eth NEUTRAL ETH (+)Ia=I_eth Ib=0 Figure 12: Tamper method #11, I/O swapped. Load connected to ETH (Nin=Nout). © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT LOAD LIVE I_part NEUTRAL I_eth ETH (+)Ia=I_eth+I_p art (+)Ib=I_part I_part=Ia-Ib Figure 13: Tamper method #12, I/O swapped. Load partially connected to ETH (Nin=Nout). © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT LIVE NEUTRAL ETH (-)Ia=I_eth Ib=0 Figure 14: Tamper method #13, Load connected to ETH. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT LIVE I_part NEUTRAL I_eth ETH (-)Ia=I_eth+I_part (-)Ib=I_part Ieth=Ia-Ib Figure 15: Tamper method #14, Load partially connected to ETH. © 2005 TERIDIAN Semiconductor Corporation, Proprietary and Confidential TERIDIAN 71M651x Power Meter IC A Maxim Integrated Products Brand 6511 Calibration for Shunt and CT Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408- 737-7600 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products.