3.2.2
LED Codes
LED “PWR” (green) - device status:
(off) power supply voltage is not present, measurement is stopped
(slow blinking once per 2 s) normal operation, ready for connection
(fast blinking once per 400 ms) device is awaiting commands in fixed baud rate (see 2.2.1)
LED “A1” and “A2” (red) - configurable/alarm LEDs:
(off) configurable (e.g. alarm off)
(on) configurable (e.g. alarm on)
(blinking) configurable (e.g. electricity meter pulse output)
“PWR”, “A1” and “A2” LEDs while firmware upgrade is in progress:
erasing main program memory
receiving new firmware
3.3
The Method of Measurement and Evaluation of Individual Variables
Measurement includes three continuously performed processes: frequency evaluation, sampling voltage and cur-
rent signals and evaluation of these sampled data.
3.3.1
Measuring the Frequency of the Fundamental Harmonic Voltage Component
Frequency of the fundamental harmonic of voltage signal is continuously measured and evaluated every 10
seconds. The measured signal is a line voltage of first phase signal modified with a low pass filter. Frequency is
assessed as a percentage of the number of full cycles of the network established within each 10 seconds and the
cumulative duration of full cycles.
3.3.2
Measurement of Voltages and Currents
Voltage and current signals are evaluated continuously without gaps. Basic evaluation interval is ten/twelve
cycles of the network (200 ms for both 50 Hz or 60 Hz network). This evaluation forms the basis for all further
calculations. All channels are sampled at the frequency of 128 samples per network cycle. Sampling is controlled
by the measured frequency at the
L
1
. If the value of the frequency is in measurable range it also controls the
sampling — sampling is automatically adjusted to the frequency change. Otherwise, the sampling runs according
to the preset nominal frequency (50 or 60 Hz). RMS voltage and currents are evaluated from the sampled values
for the measuring cycle according to equations:
Line-to-Neutral voltage (RMS):
U
1
=
v
u
u
t
1
n
n
X
i
=1
U
2
1
i
Line-to-Line voltage (RMS):
U
12
=
v
u
u
t
1
n
n
X
i
=1
(
U
1
i
−
U
2
i
)
2
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