Datasheet
STPM01 calibration STPM01
50/60 Doc ID 10853 Rev 8
9 STPM01 calibration
Energy meters based on STPM01 device are calibrated in a fast and easy way. The
calibration is essentially based on the single calibration of the voltage and current channel
considering their RMS values rather than on the frequency of output pulse signal. When the
two channel are calibrated all the other measurement are calibrated too. This allows the
calibration to be performed in only one point shortening the production time of the meter.
This procedure is possible due to the below key points:
– Device is compound of two independent meter channels for line voltage and current
respectively. Each channel includes its own digital calibrator, to adjust the RMS in the
range of ±12.5 % in 256 steps, and digital filter, to remove any signal DC component.
All final results are not subject to calibration procedure because they are achieved
from such corrected signals by mathematical modules implemented by hardwired
DSP.
– Device computes different kind of energies: active, reactive and apparent. The active
energy is produced without 2nd harmonic of line frequency. It also computes RMS
values of measured voltage and current.
– Device produces an energy output pulse signal but information can also be read
through serial port interface, SPI, and communication channel.
– Device has an embedded memory, 56 bits, used for configuration and calibration
purposes. The value of these bits can be read or they can be changed temporarily or
permanently through SPI communication channel.
Let’s consider the basic information needed to start the calibration procedure:
The following typical STPM01 parameters and constants are also known:
Table 18. Working point settings
Line RMS voltage V
n
(230V)
Line RMS current I
n
(5A)
Power sensitivity P (LED: P=128000 pulses/kWh, stepper motor: PM=P/64= 2000 pulses/kWh)
Shunt sensor K
S
0,42 mv/A
Table 19. Device constants
Parameter Value Tolerance
Internal reference voltage V
BG
1.23 V ± 2%
Internal calculation frequency f
M
2
23
Hz ± 50 ppm
Amplification of voltage ADC A
V
4± 1%
Amplification of current ADC A
I
8, 16, 24, 32 ± 2%
Gain of differentiator G
DIF
0,6135
Gain of integrator G
INT
0,815
Gain of decimation filter G
DF
1.004
RMS voltage register length B
V
2
11
RMS current register length B
I
2
16
Constant D
UD
2
17