Cirrus Logic AN366 User Manual
AN366
Application Note
CS5480/84/90 Energy Measurement IC Calibration
1 Introduction
The Cirrus Logic CS5480/ 84/ 90 energy measurement IC is designed with industry-leading calibration algorithms
that simplify measurement applications. The CS5480/84/90 calibration is engineered so power meter manufacturers
can use low-cost components to achieve highly accurate power measurement. Calibration methods specified by IC
manufacturers can vary substantially despite the power meter manufacturers’ requirements to comply with tightly
regulated standards. This application note will introduce the procedures available for calibrating the CS5480/84/90
devices, empowering power meter manufacturers to exceed industry standards.
2Overview
This application note covers system scaling concepts, including hardware scaling, analog front end (AFE) scaling,
and controller (MCU) scaling. The relationship between full-scale measurements and AFE measurements is
discussed, and a corresponding application processor example is presented. The typical hardware configuration
required to perform calibration and compensation is also presented. Then the types of calibrations in the
CS5480/84/90 are detailed. The calibration and compensation procedure is provided in a step-by-step process that
determines the AFE calibration and compensation constants.
Flow diagrams are provided for each calibration and compensation process. The customer demonstration board
(CDB5484U) is used to illustrate the calibration process and provide examples of the serial port reads / writes
transmitted at each calibration step.
Below are the calibration essentials discussed in this document:
- System Scaling
- Types of Calibration and Compensation
- Calibration and Compensation Procedure
- Calibration and Compensation Example with Hardware Configuration
3 System Level Configurations
Upon power-up, the CS5480/84/90 requires an initial register configuration before executing power measurements.
One of the key configurations is adjusting the system scaling for the power meter application. The key scaling
constants are identified through calibration and compensations performed at the power meter manufacturer. After
the configuration and calibration constants are established, the calibration constants are downloaded during a
normal power-on reset. The application will start conversions and report power and input performance over time.
During power conversions and calculations, the analog inputs are sampled at 512 kHz, decimated down to 4 kHz
high-rate conversion cycles. The high-rate samples are averaged to produce a 1 second low-rate power
accumulation measurement, which is used to update registers and, when enabled, generate pulses that represent
the power results (N = 4000, MCLK = 4.096 MHz). The CS5480/84/90 performs signal conditioning along the digital
data path, which improves the accuracy of the power meter measurements. Signal conditioning is provided in the
high-rate path (gain, phase, and DC offset) and in the lower rate path (no load current RMS offset, AC offset, active
and reactive power offset).
Cirrus Logic, Inc.
http://www.cirrus.com
Copyright Cirrus Logic, Inc. 2012
(All Rights Reserved)
MAY’12
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3.1 System Scaling Overview
The maximum voltage, current, and power measurements are unique in each meter design and dependent on
the sensors used in the measurement of these parameters. The CS5480 / 84/ 90 solves this problem using scaling. Instead of recording the actual voltage, current, or power sensed by the power meter, the IC records a ratio
of each measurement that is proportional to the meter’s full-scale. Using this ratio, the actual voltage, current,
and power can be calculated based on the values of the AFE registers.
There are two methods of obtaining the most recent power measurement readings:
- Voltage, current and power measurements are read directly from registers using the serial port.
- Power measurements are accumulated using the pulses on the DO pin(s).
Both methods are dependent on full-scale calibration to accurately scale the most recent power measurement.
Traditional power meters typically use the pulse accumulation method. Since calibration constants are recorded
in registers and power measurements are reported by register reads/writes, this document will focus on the register read/write method.
To use the built-in calibration functions, an understanding of the scaling factors due to the different system components within a typical meter is required. Below are three general scale factors in the signal path:
- Hardware Scale: The real voltage and currents are provided to the meter using sensors that must be
attenuated on the meter board or by the sensor before applying the sensed signal to the input of the
CS5480/84/ 90.
- AFE Register Scale: The device stores information for each voltage, current, and power parameter to
internal registers. Each register value is scaled to a range of ±1 or 0 to 1 and stored in a 24-bit register.
The values measured at the input (for example, 500mVpp) are stored as a scaled version of input signal
amplitudes. Refer to the CS5480/ 84/ 90 data sheet for register formats. The gain and offset registers
are scaled to be within the range of 0 to 4 and ±1, respectively. Therefore, the MCU does not read the
sensor output voltage and current; instead, it reads the scaled values recorded in the registers.
- MCU Scale: The MCU is typically used to rescale the real voltage, current, and power values for display.
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3.2 System Scale Example
CS 5480 / 84 / 90
(AF E)
LN
VIN-
VIN+
IIN+
IIN-
Application
Pro cessor
LOAD
CT
Pulse
Pulse
OR
Display
Power
19 .2 kW
240 V
RMS
,
80 A
RMS
176 m V
RMS
,
35 m V
RMS
19 .2 kW
240 V
RMS
,
80 A
RMS
Pavg: ±0.36
V
RMS
: 0.6
I
RMS
: 0.6
Hardware
Scale
AFE
Scale
MCU
Scale
19 .2 k W
240 V
RMS
,
80 A
RMS
Input Output
Seri al
Port
Figure 1 illustrates an example of the system scaling.
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Figure 1. System Scaling
- Hardware Scale: The CS5480/ 84 /90 inputs are scaled using attenuation circuits that apply a maximum
input amplitude of 176mV
RMS
or 35mV
, which is dependent on an AFE gain setting of 10x gain or
RMS
50x gain, respectively.
- AFE Scale: The AFE registers record input levels that are displayed as a ratio of the most recent
measurement to the maximum RMS voltage and RMS current. The maximum RMS register value is
generated using a 0.6 ratio. The register value is read as a 24-bit hexadecimal number, which is
proportioned to represent a 0.6 V
the maximum power is P
- MCU Scale: The MCU is required to read all registers and interpret the 24-bit hexadecimal numbers
MAX
= V
full scale. At maximum voltage (0.6) and maximum current (0.6)
RMS
RMSMAX
× I
RMSMAX
= 0.6 × 0.6 = 0.36.
based on full-load conditions. Knowing the maximum hardware scaling and the most recent AFE
register values in relation to the full-scale input, the MCU routines are able to calculate the actual power
measurements.
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RMS 1 Current (I1
RMS
) – Page 16, Address 6
Default = 0x00 0000
I1
RMS
contains the root mean square (RMS) values of I1, calculated during each low-rate interval.
This is an unsigned value in the range of 0 value 1.0, with the binary point to the left of the MSB.
RMS Voltage 1 (V1
RMS
) – Page 16, Address 7
Default = 0x00 0000
V1
RMS
contains the root mean square (RMS) value of V1, calculated during each low-rate interval.
This is an unsigned value in the range of 0 value 1.0, with the binary point to the left of the MSB.
MSB LSB
2
-1
2
-2
2
-3
2
-4
2
-5
2
-6
2
-7
2
-8
.....
2
-182-192-202-212-222-232-24
MSB LSB
2
-1
2
-2
2
-3
2
-4
2
-5
2
-6
2
-7
2
-8
.....
2
-182-192-202-212-222-232-24
Figure 2. Example of I
RMS
and V
RMS
Registers
VALUE
Decimal
1
2
24
1–
------------------
hex2dec VALUE
Hexidecimal
=
[Eq: 1]
V
PEAK
V
RMS
2 0.6 2 0.85===
[Eq: 2]
3.3 AFE Scaling Range
The CS5484 full scale RMS register values are commonly reported as 0.6 when the inputs are at a maximum
level. The ratio of the AFE inputs to full scale defines the reference point for all other input levels. The 24-bit
I1
and V1
RMS
does not match the scaling for power (signed). Section 6.2 Main Calibration Flow Diagram Using the CDB5484
on page 29 describes the scaling ratio of the AFE inputs when maximum input levels are applied.
registers are defined in Figure 2. Note that the digital scaling for RMS current (positive only)
RMS
Use Equation 1 to convert the hexadecimal value to a decimal value:
Using Equation 1, the following key values are identified:
Key RMS Register Values Range (0 to 1) Decimal Value Register Value
Maximum RMS Register 1 0xFFFFFF
Maximum RMS Input 0.6 0x999999
Half RMS Input 0.36 0x5C28F6
No Load Input 0 0x000000
If a sine wave is applied to the voltage channel input at full scale, then the peak voltage can be determined using
Equation 2:
The V
The CS5480/84/ 90 provides a current channel scale register that allows a small load current during calibration.
By default, the range is 0.6 (full-scale current load), but this value can be adjusted according to the load current
available.
PEAK
register will have a maximum input margin of 15%, which prevents clipping.
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ReportedCurrent
ACTUAL
Current
REGISTER
Current
FULLSCALE
0.6
-----------------------------------------------------------------------------------------------------------
0.25 50A
0.6
-----------------------------
20.8A===
[Eq: 3]
ReportedPower
ACTUAL
Power
REGISTER
Power
FULLSCALE
0.36
---------------------------------------------------------------------------------------------------
=
Power
REGISTER
Vch
FULLSCALE
Ich
FULLSCALE
0.36
---------------------------------------------------------------------------------------------------------------------------------------------
=
0.15 140 50
0.36
---------------------------------------------
2916.7W==
[Eq: 4]
Active Power 1 (P1
AVG
) – Page 16, Address 5
Default = 0x00 0000
Instantaneous power is averaged over each low-rate interval (SampleCount samples) and then added
with power offset (P
OFF
) to compute active power (P
AVG
).
This is a two's complement value in the range of -1.0value1.0, with the binary point to the right of the
MSB.
Active Power 2 (P2
AVG
) – Page 16, Address 11
Default = 0x00 0000
Instantaneous power is averaged over each low-rate interval (SampleCount samples) to compute active
power (P2
AVG
).
This is a two's complement value in the range of -1.0value1.0, with the binary point to the right of the
MSB.
MSB LSB
-(20)2-12
-2
2
-3
2
-4
2
-5
2
-6
2
-7
.....
2
-172-182-192-202-212-222-23
MSB LSB
-(2
0
)2-12
-2
2
-3
2
-4
2
-5
2
-6
2
-7
.....
2
-172-182-192-202-212-222-23
Figure 3. Example of P1
AVG
and P2
AVG
Registers
3.4 Application Processor Scaling Example
The scaling example below demonstrates how to convert from the current register value to the reported current
using the full-scale value. The specified full-load (Current
(Current
REGISTER
) is 0.25 (0x40 0000), then the actual current value (ReportedCurrent
FULLSCALE
the application processor using Equation 3.
Use Equation 3 to convert the current register value to the real current:.
Scaling for power requires a change in the denominator to reflect a power scaling ratio of 0.36, which is equal
to the voltage (0.6) multiplied by current (0.6). The input full load (Ich
voltage (Vch
register (Power
FULLSCALE
REGISTER
) is 140V. If the present load is applied to the meter results in a power
) reading of 0.15 (0x13 3333), then the application processor needs to convert the
power register value to the real current value. Use Equation 4 to convert the power register value to real reported
power.
) is 50A. If the AFE current register value
) is calculated by
FULLSCALE
ACTUAL
) is 50A and the maximum
Cirrus Logic power meters are bidirectional, which allows power to be measured in both directions (consumed
or delivered). This reduces the digital scaling by one bit due to polarity, unlike the unsigned RMS current register.
The 24-bit P1
and P2
AVG
registers are defined in Figure 3.
AVG
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VALUE
Decimal
MSB–
1
2
23
1–
------------------
hex2dec VALUE
Hexidecimal
=
[Eq: 5]
Use Equation 5 to convert the hexadecimal value to a decimal ratio value:
Using Equation 5, the following table identifies the key values.
Key Power Register Values Range (-1 to 1) Decimal Value Register Value
Maximum Power Register 1 0x7FFFFF
Maximum Power Input 0.36 0x2E147B
No Load Input 0 0x000000
4 Types of Calibration and Compensations
Calibration is self-contained within the CS5480/ 84/ 90, and all calculations are performed by the device and
stored in internal registers. Compensations require that the MCU perform some of the calculations and then
store the results back into the CS5480/ 84 /90 registers. Since the CS5480/ 84 / 90 does not have non-volatile
memory (NVM), permanent storage of calibration and compensation must be placed in the MCU NVM and reloaded after any AFE reset condition.
In general, each calibration and compensation requires the following steps:
1. Configure the CS5480/84/ 90 initial conditions
2. Apply the analog input with stimulus from an accurate source
3. Enable the desired calibration
4. Execute calibration
5. Read the results
6. Calculate the new register values for compensations
7. Store the results in the AFE and NVM
It is common to perform calibration and compensation simultaneously. For example, since an AC gain calibration
and a phase compensation require a similar input signal to be applied to the current and voltage channels, calibration and compensation are performed simultaneously.
6 AN366REV2
Figure 4 illustrates a typical hardware configuration for calibration and compensation:
AC
LOAD
AC
SOURCE
CS5480 /84 /90
(A FE)
LN
VIN -
VIN +
IIN +
IIN -
Application
Processor
LOAD
CT
Pulse
Pulse
OR
Display
Power
Seri al
Port
Reference
Meter
Optical
Sensor
Calibration
Controller
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Automation can be established by a calibration controller that starts the calibration and/or the compensation,
performs the required calculations, and finally initiates the storage of results. A calibration controller will control
the AC source and load during calibration by adjusting the load for different AFE input conditions. The controller
will also monitor the precision reference meter to confirm that load adjustments have been successfully executed, and the optical accumulation results are accurate from the Cirrus AFE. Communication from the controller
to the Cirrus AFE is processed through the meter application processor to the calibration controller. Calculations
and NVM results stored within the application processor are initiated by the controller when the calibration is
completed.
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Figure 4. Calibration and Compensation Hardware Configuration
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V
RMS
*
, I
RMS
*
Registers
V*, I*, P*, Q
*
Registers
N
I
GAIN
*
, V
GAIN
*
Registers
*
Denotes readable/writable register
Ϯ Applies only to the curr ent path
N
N
-1
N
DC
RMS
-1
RMS
0.6(Scale
*
Ϯ
)
P
AVG
*
, Q
AVG
*
Registers
N
N
Modulator
I
DCOFF
*
, V
DCOFF
*
Registers
PC
Register
Sinc IIR
SYS
GAIN
Register
IN
P
OFF
*
, Q
OFF
*
Registers
I
ACOFF
*
Ϯ
Register
4.1 AFE Calibrations
The CS5480/84/90 AFE incorporates three calibrations: gain, AC offset, and DC offset. Gain calibration is always required. AC offset calibration is only required when I
offset calibration is made available but not recommended for AC power meters. Instead, high-pass filters are
used to remove DC offset. The high-pass filter included in the CS5480/ 84 /90 will remove any DC offset in real
time, and it is the best choice for AC power meters.
Figure 5 shows a flow diagram of the calibration process included in the Cirrus AFE. Refer to the CS5480/84/90
data sheet for detailed information.
needs to be accurate at low input levels. DC
RMS
Figure 5. Calibration Data Flow
4.1.1 DC Offset Calibration
DC offset calibration is designed to remove the DC component from the ADC output. DC offset calibration
is seldom used in AC power meters. The high-pass filter is the recommended choice and should be enabled
at the modulator output, as illustrated in Figure 5.
4.1.2 Gain Calibration
Gain calibration will adjust the input for hardware and sensor variations and customer-specific inputs. It is
recommended to use full-load conditions (full-scale voltage and current). (For non-full-load conditions, see
section 4.1.2.1 on page 8). When the full current load is not available, the CS5480/84/90 allows the scale
register to adjust for lower current loads to be provided. (See 3.3 on page 4 for adjusting the scale register.)
After gain calibration, full-scale input will yield:
- The Voltage RMS register, V
- The Current RMS register, I
- The Active Power register, P
- The Reactive Power register, Q
- The Apparent Power register, S, value: 0.6
4.1.2.1 When AC Source or AC Load Are Less Than Ideal
If the AC source or AC load are less than ideal, the meter can still be calibrated with an accurate reference
meter using the Non-full-scale Gain Calibration procedure on page 9. It is common to see an AC load set to
15A actually measure in the range of 14.55 A to 15.45A using a reference meter. When using the full-scale
, value: 0.6
RMS
, value: 0.6
RMS
, value: 0.6 0.6 = 0.36 at PF = 1
AVG
, value: 0.6 0.6 = 0.36 at PF = 0
AVG
0.6 = 0.36
current, it may be necessary to use the Non-full-scale Gain Calibration procedure on page 9 to account for
inaccurate resources.
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V
GAIN pre
V
MAX
V
REF
---------------
2
22
=
[Eq: 6]
I
GAIN pre
I
MAX
I
REF
------------
2
22
=
[Eq: 7]
4.1.2.2 Non-full-scale Gain Calibration
When resources are limited, it may be necessary to provide non-full-scale amplitudes and perform built-in
calibration to provide the maximum voltage and current during calibration. To perform a non-full-scale calibration, the initial gain register conditions of the device must be identified before calibration. Usually, initial
gain register conditions are set to a default value of one, but this is not required. Instead, the initial gain register conditions are set to accommodate the non-full-scale input calibration. Before calibration is executed,
the gain register can be set using the following equations:
where:
V
GAIN(pre)
I
GAIN(pre)
V
MAX
I
MAX
V
REF
Value stored in voltage gain register (page 16, address 35) before calibration starts
Value stored in current gain register (page 16, address 33) before calibration starts
Maximum voltage of the meter defined by customer
Maximum current of the meter defined by customer
Voltage of the line just before calibration as measured with reference meter assumes
stable input
I
REF
Load current just before calibration as measured with reference meter assumes stable
input
Follow the steps below to perform a non-full-scale gain calibration:
1. Set the line voltage and load current V
2. Confirm that the reference meter shows V
3. Set V
GAIN(pre)
per Equation 6 and I
GAIN(pre)
and I
REF
REF
REF
and I
per Equation 7.
, respectively.
of the input.
REF
4. Send the calibration command.
5. After calibration, the meter is adjusted for a full-scale voltage of V
measuring the V
REF
and I
measurements.
REF
MAX
and I
and will currently be
MAX
Reference Limits
The calibration line voltage (V
) or load current (I
REF
) must not be set too low. It is recommended to keep
REF
the register values at a minimum of ½ of the maximum levels. Since the gain register can be set to a maximum value of 4, the input could be set to ¼ of the maximum levels. It is not recommended to set the input
to ¼ of the maximum levels due to variations in setup conditions. If the input is too low, the gain register will
set the default value of one after calibration.
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I
SCALE
I
REF
I
MAX
------------
0.6 2
23
=
[Eq: 8]
Current Scale Register
To perform calibration with less than full scale load without using the above procedure, it is possible to set
the current channel's Scale register. The current channel calibration data path contains a Scale register
(page 18, address 63) that can be adjusted before calibration to accommodate the non-full-scale load.
where:
I
SCALE
I
MAX
I
REF
Value stored in the Scale register before calibration
Maximum current of the meter defined by the customer
Load current before calibration, as measured with a reference meter, assuming stable
input
Follow the steps below to set the current channel’s Scale register.
1. Set the load current, I
2. Confirm that the reference meter shows V
(assuming V
REF
is set to full scale).
REF
and I
REF
REF
of the input.
3. Set the Scale register per Equation 8.
4. Send the calibration command.
5. After calibration, the meter is adjusted for a full-scale voltage of V
measuring the V
REF
and I
measurements.
REF
MAX
and I
and will currently be
MAX
6. The Scale register is not in the normal data path but instead in the calibration path.
4.1.3 AC Offset Calibration
Following gain calibration, there may still be some AC offset remaining. AC offset calibration will allow for
the removal of the remaining offset. The AC offset effects are only applicable to the I
input. The AC offset calibration only needs to be performed when I
readings are required to span a large
RMS
registers at small
RMS
dynamic range with high accuracy.
4.2 Available Compensations
Three compensations are available in the CS5480/84/ 90: phase, no-load active power, and no-load reactive
power offset.
4.2.1 Phase Compensation
Phase compensation adjusts phase mismatches between the voltage and current channels. Setting the current to lag the voltage by 60º (the center of the COS range of 0º - 90º) allows the system to distinguish additional or less phase delay from the power factor (PF) directly. Follow the steps below to perform this
compensation:
1. Apply source at full scale with a 60º phase shift (PF = 0.5 lagging)
2. Start continuous convert
3. Read the PF register and calculate:
Phase error = ACOS(register PF)-60º
4. Calculate phase compensation (PC) register (MCLK=4.096MHz):
50Hz PC register = phase error/0.008789
60Hz PC register = phase error/0.010547
Phase error can be adjusted when it falls within ±8.99º at 50Hz or ±10.79º at 60Hz. Figure 6 shows the
phase offset error range. When phase error is below -4.5º at 50Hz or -5.4º at 60Hz and above 0 º, it is necessary to adjust both coarse compensation and fine compensation. The coarse and fine compensation settings for each region are shown in Figure 6.
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0º
Before Calibration V is delayed from I
Delay added to I
8 .99 º @ 50 H z
10.79 º @ 60Hz
4.5º @ 50Hz
5.4º @ 60Hz
-4.5º @ 50Hz
-5.4º @ 60Hz
-8.99º @ 50 Hz
-10 .79 º @ 60Hz
Before Calibration I is delayed from V
Delay added to V
Set C PC C = 11 of 2OW R on V
+ FPC C prov i des adjus tm ent
Set C PC C = 10 of 1OW R on V
+ FPC C prov i des adjus tm ent
Clear CPCC = 00
+ FPC C prov i des adjus tm ent
Set CPCC = 01 of 1OWR on I
+ FPC C prov i des adjus tm ent
Figure 6. Phase Compensation and Phase Offset Error
4.2.2 No Load Power Compensation
There are two power compensations in the CS5480/ 84 / 90: active and reactive power offset. When no load
is applied, the average active power register, P
, and average reactive power register, Q
AVG
AVG
offsets. To remove any remaining active or reactive power, it is necessary to perform the following compensation:
- Apply full scale voltage source
- Apply no load to the current channel(s)
- Start continuous conversion
- Read P
- Write -P
and Q
AVG
and -Q
AVG
AVG
AVG
register
to P
OFF
and Q
, respectively
OFF
, may have
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5 Calibration and Compensation Procedures
A CS5480/84/ 90 power meter normally has two modes of operation: calibration, which is executed only once at the
factory, and normal operation in the field.
Calibration will compensate for system-level errors and is only performed at the factory. Normal operation is a
continuous running mode (continuous conversion mode) or user-initiated, single execution mode (single conversion
mode). Most designs are continuously running and use the continuous conversion command. Normal operation is
resetting the device, loading calibration and configuration information from non-volatile memory, and executing
continuous conversion command. The MCU then needs to read various device registers to obtain the power, current,
and voltage. As these registers are updated, the MCU will need to post the information to the user interface. This is
accomplished by using DO pin interrupts or by periodically reading the status register. The default configuration of
the part sets most of the registers to a common configuration. When continuous conversion is performed, the device
will provide most register updates once per second (default at reset).
The normal field operation is simple and there is no need for extensive computation by the MCU. A simple, low cost
MCU may be used to assist the normal operation.
5.1 Normal Operation Procedure (Performed at Every Reset in the Field)
The following procedure outlines the steps required to put the meter in normal operation mode. Figure 7 shows
a simplified flow chart for the normal operation in the field.
1. Reset the CS5480/84 / 90.
2. Restore configuration and control registers.
3. Restore the V
GAIN
and I
registers from the non-volatile memory (NVM).
GAIN
4. If needed, restore the offset registers from NVM.
5. If needed, restore the phase compensation registers from the NVM.
6. If needed, restore the no load compensation to the P
OFF
and Q
OFF
7. Send the single conversion command to the CS5480/84/90.
8. Confirm that the register checksum is valid, or return to step 1.
9. Send the continuous conversion command to the CS5480/84/90.
10. Enable and clear DRDY.
11. Poll DRDY.
12. If DRDY is set, clear DRDY.
13. Read I
RMS
, V
RMS
, and P
. Scale the I
AVG
Amps = Full_Scale_Current
Volts = Full_Scale_Voltage
Watts = Full_Scale_Power
(I
(V
(P
RMS
RMS
AVG
RMS
/0.6)
/0.6)
/0.36)
, V
RMS
, and P
back into true value by:
AVG
14. Loop back to "Poll DRDY" step.
registers from the NVM.
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START
CONTINUOUS
CONVERSION
0xD5
CLEAR
DRDY
READ IRMS,
VRMS, PAVG
DRDY
SET?
POWER UP
RESTORE
CONFIGURATION
and CONTROL
REGISTERS
From NVM
RESTORE
GAIN
REGISTERS
From NVM
RESTORE
OFFSET
REGISTERS
From NVM
RESTORE
POFF and QOFF
REGISTERS
CLEAR
DRDY
CALCULATE
VOLTS = FS_Voltage · (VRMS/0.6)
AMPS = FS_Current · (VRMS/0.6)
WATTS = FS_Scale _Pow er · (VRMS/0.36)
RESET
VALID
REGISTER
CHECKSUM
?
SINGLE
CONVERSION
YES
NO
YES
NO
Figure 7. Normal Field Flow
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5.2 Full Calibration and Compensation Procedure (Performed Once at Factory)
The following procedure shows the steps required to perform calibration and compensation. A flow chart showing the full calibration procedure is shown in Figure 5.
1. Power up the CS5480/84/90 device.
2. Reset the CS5480/84 / 90 device.
3. Verify the register checksum to confirm the reset is successful.
4. Restore configuration and control registers.
5. Connect the reference line voltage and load current to the meter with a phase angle of 60º current lagging.
6. If the reference load current is not the full load, set the Scale register to a ratio of 0.6 2
current ÷ full scale current. See Non-full-scale Gain Calibration on page 9 if the reference line voltage is
lower than the maximum line voltage.
7. Perform continuous conversion (0xD5 command) for 2 seconds.
8. Stop the continuous conversion (0xD8 instruction).
9. Read I
attached by verifying if the I
RMS
, V
RMS
, P
, and PF, and confirm the reference voltage and current signals are correctly
AVG
RMS
, V
RMS
, P
, and PF are in a reasonable range.
AVG
10. Clear DRDY status bit.
11. Send AC gain calibration command (0xFE) to the CS5480/ 84 /90.
12. Wait for DRDY to be set.
23
reference load
13. If needed, perform phase compensation, AC offset calibration, and power offset correction.
14. Send continuous conversion (0xD8 command).
15. Verify measurement accuracy. Check the setup or fail the meter if the accuracy is not within specifications.
16. Read V
GAIN
, I
GAIN
, I
ACOFF
, P
OFF
, Q
, PC, and register checksum and save them into flash/eeprom.
OFF
17. Calibration completed.
14 AN366REV2
RESET
(See Note 1)
ROGOWSKI
SENSOR?
ENABLE
HIGH PASS
FILTER
ENABLE
INTEGRATOR on
CURRENT &
HIGH PASS on
VOLTAGE
FULL LOAD
AVAILABLE ?
APPLY
REFERENCE
LINE VOLTAGE
AND LOAD
CURRENT
(Note 5)
SET SCALE
REGISTER
0.6 · LOAD ÷ FS
(Note 6)
READ
IRMS, VRMS,
PAVG, QAVG, PF
START
CONTINUOUS
CONVERT
0xD5
STOP
CONVERSIONS
0xD8
SEND AC GAIN
CALIBRAT ION
0xFE
ACCURACY
IN SPEC?
CHECK
SETUP or
FAIL
READ VGAIN,
IGAIN, IACOFF,
POFF, QOFF, PC,
RegChk
STORE
CALIBRAT ION
CONSTANTS &
REGISTER
CHECKSU M
POWER UP
CALIBRAT ION
COMPLETE
DC
MEASUREMENT?
PERFORM
DC
CALIBRAT ION
DRDY
SET?
SINGLE
CONVERSION
YES
NO
YES
NO
YES
NO
YES
NO
YES
NO
YES
NO
VALID RESET
CHECKSUM?
(Note 3)
CONFIRM
REFERENCE
SIGNALS ARE
APPLIED
CORRECTLY
Tsettle =
2000ms
(Note 2)
SampleCount (N) =
16,000
(Note 2)
START
CONTINUOUS
CONVERSION
AND VER IF Y
METER
ACCURACY
CLEAR
DRDY
PERFORM PHASE
COMPENSATI ON,
IACOFF CALIBRATION,
and POWER OFFSET
CORRECTION if
NECESSARY
Note 1: The default setting for all registers should be set before performing calibration. Resetting the device restores the default setting
for all registers.
Note 2: Larger numbers in the Tsettle and SampleCount registers will increase calibration precision.
Note 3: Other configurations and controls might be necessary.
Note 4: For an expanded view showing more information about the main calibration flow, see Main Calibration Flow Diagram Using the
CDB5484 on page 29.
Note 5: See Non-full-scale Gain Calibration on page 9.
Note 6: Scale register is only in calibration path and does not require resetting to 0.6 after the calibration.
Figure 8. Main Calibration Flow
AN366
AN366REV2 15
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