2
2
2
2
_
_
2
1
2
APPARENT REF
ACTIVE
APPARENT UUT
ACTIVE
C
P
P
P
P
fV
S
§
·
¨
¸
©
¹
(Im
)
(Im
)
Im
Im
max
min
max
REF
ax
REF
ax
UUT
ax
UUT
ax
WIRE
V
V
V
V
R
I
I
I
|
1 %
1 %
UUT
%Error
Error
Error of V
at this load
1
1 %
REF
n
n
UUT
UUT
P
PGAIN
PGAIN
Error of V
at this load
P
u
u
Calibration Procedures
3.
Calibrating PGAIN
(a) Same condition as above (the power factor at this calibration point should be 1 or very close to 1).
(b) Note the percentage error on voltage at this point.
(c) Calculate PGAIN gain so that power is of the same percentage error as voltage at this point.
where
•
PGAIN
n+1
is the new power calibration factor
•
PGAIN
n
is the original power calibration factor
•
P
REF
is the reference meter power reading at the power set for PGAIN calibration
•
P
UUT
is the unit under test power reading at the power set for PGAIN calibration
(6)
Or if percentage error is used (as with the provided calibration software):
(7)
(d) Write and apply the calibrated PGAIN.
3.3.2 Calibration of Compensation Resistance and Capacitance
After the calibration of VGAIN, IGAIN and PGAIN, follow these steps to calibrate the compensation to wire
resistance and EMI capacitance.
1. Calibrating RES
(a) Calculate RES with the give equation.
where
•
R
WIRE
is the estimated wire resistance
•
V
REF(Imax)
is the reference meter voltage reading at the current set for IGAIN calibration
•
V
UUT(Imax)
is the unit under test voltage reading at the current set for IGAIN calibration
•
I
max
is the current set for IGAIN calibration
(8)
(b) Write and apply the calibrated RES (note that the resistance is in units of 1/256
Ω
)
2. Calibrating CAP
(a) Set to No / Lowest possible load.
(b) Set VIN to low line voltage.
(c) Calculate CAP with the given equation.
where
•
C is the estimated EMI filter capacitance
•
V is the voltage set for calibration of C
•
P
APPARENT_REF
is the apparent power reading of the reference meter at the setting for this calibration
•
P
APPARENT_UUT
is the apparent power reading of the unit under test at the setting for this calibration
•
P
ACTIVE
is the active power reading of the reference meter
(9)
(d) Write and apply the calibrated CAP (note that the capacitance is in units of 1/64 µF).
21
SLAU587 – August 2014
Calibration Techniques
Copyright © 2014, Texas Instruments Incorporated