User Manual i4MC&V/EN M/C
iSTAT i4MC&V
Page 20
4. INSTRUMENTATION
4.1 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 i4MC/V uses a true RMS (root-mean-square) measurement technique that provides
accurate measurement with harmonics present up to the 63rd harmonic (at 50Hz). The
i4MC/V reads 128 samples per cycle (at 50Hz) and the true RMS measurement is obtained
using these sampled values. At higher signal frequencies the number of samples reduces
and the number of harmonics included in the calculations is also reduced.
4.2 Glossary
The follo
wing terms are used:
TABLE 4-1: GLOSSARY
Term Explanation
RMS Root Mean Square value
Flash
Type of a memory module that keeps its content in case
of power supply failure
MODBUS Industrial protocol for data transmission
QDSP Software for iSTAT family
AC Alternating current
THD Total harmonic distortion
MD
(maximum demand)
Measurement of average values in time interval
Sample factor (Mv)
Defines a number of periods for measuring calculation on
the basis of measured frequency
Averaging interval (Mp)
Defines frequency of refreshing displayed measurements
on the basis of a Sample factor
4.3 Supported Measurements
The follo
wing tables show the measurements available on the i4MC and i4MV; all values are
available over the communications
TABLE 4-2: i4MC
Current I
1
Frequency f
THD of current I
1
Internal temperature
Dynamic Demand I
1
Max Demand since last reset I
1
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