STPM11_08 STMICROELECTRONICS [STMicroelectronics], STPM11_08 Datasheet - Page 38

• Manufacturer Part Number: STPM11_08
• Description: Single phase energy metering IC with pulsed output and digital calibration
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Table 18.
Note:
38/45
Value of Calibrator
Frequency at LED
Voltage divider
Voltage divider resistor
Description
Each calibrator value can be changed from a binary form to a decimal correction form, using
the following formula:
Kv=(Cv/128)*0.125 + 0.75 and the same for Ki.
Let us choose as initial value Ai=32
Calibration results
From the target power constant C
which are applied to the meter under calibration, the error of power measurement can be
calculated:
err = 100(fx/f -1) [%], where fx is the real frequency read at LED output.
Now, a final unit less power reduction factor can be calculated:
p
This final power reduction factor can be considered as a product of voltage and current
reduction factors which are produced from corresponding calibration constants. So, an
obvious solution to obtain the voltage and current reduction factors is to calculate a common
reduction factor as a square root of pF. This result must fall within the indicated range,
otherwise the device cannot be calibrated:
768 ≤ R = 1024 pF + 0.125 < 1024
In order to obtain the corresponding calibration constants, the reduction factor must be
transformed:
CV = CC = R - 768
By using separately the integer and the fractional part of the common reduction a better fit of
calibration constants can be produced. Simply, let's set one of the two calibration registers
(e.g. CV) to the lowest integer value of R, while the other (CC) should be set to the nearest
integer value of R. Examples:
R-768=128.124; in this case set CV=128; set CC=128
R-768=127.755; while in this other one set CV=127; set CC=128.
STPM13/14: each current channel must be calibrated separately. In order to do this, follow
these steps:
Apply the nominal test voltage to the voltage sensor, and the nominal test current to the
primary current channel sensor. Do not apply such current on the secondary current
channel sensor.
Adjust the voltage and primary current calibrators (see above).
Disconnect the nominal test current from the primary current channel sensor, and apply it to
the secondary current channel sensor.
Adjust only the secondary current calibrators, so that the same power is computed.
F
= (p
D
- err)/100
Kp = Kv*Ki = 0.765625
f = P*In*Vn/3600000 = 40.8889 Hz
Sv = (F*DL*Vbg
R1=R2*(1000/Sv-1)
2
)/(fM*Vn*In*Gv*Gi*Kp*Ai*Av*Si)= 0,6324mV/V
P
of the meter and the actual values of V
Value
RMS
and I
RMS
,