User Manual
M2x2/EN M/F
iSTAT M2x2
Page 17
8.
INSTRUMENTATION
8.1
Measurements
With the increase in harmonics present in today's power systems, due to the increased use
of electronic loads such as computers, variable frequency drives, etc. it is important, when
accurate monitoring of electrical parameters is required, to use a measuring technique that
allows for their presence. Conventional measurement methods, that use a mean sensing
technique, respond to the mean or average of the input waveform. This is only accurate
when the input waveform approaches a pure sinusoid.
The
M2x2
uses a true RMS (root-mean-square) measurement technique that provides
accurate measurement with harmonics present up to the 63
rd
. The
M2x2
reads 128 samples
per cycle and the true RMS measurement is obtained using these sampled values.
The
M2x2
display can display the measured values in a number of preset display views or
the user can customise the display. An example is shown in figure 9.1 below.
FIGURE 9-1 : PRESET DISPLAY SHOWING VOLTAGE, CURRENT AND POWER IN PHASE 1
8.2
Glossary
The following terms and symbols are used:
TABLE 9-1 : SYMBOLS
M
v
Sample factor
M
P
Averaging interval
U
f
Phase voltage (U
1
, U
2
or U
3
)
U
ff
Phase-to-phase voltage (U
12
, U
23
or U
31
)
N
Total number of samples in a period
n
Sample number (0
n
N)
x, y
Phase number (1, 2 or 3)
i
n
Current sample n
u
fn
Phase voltage sample n
u
fFn
Phase-to-phase voltage sample n
f
Power angle between current and phase voltage f (
1
,
2
or
3
)
U
u
Voltage unbalance
U
c
Agreed supply voltage
