Tettex MIDAS 2881, Operating Instructions Manual

Page: 28 / 164

18 Functional Description
5 Functional
Description
5.1 System Overview
To be able to execute correct and reproducible measurements it is essential to understand
how the MIDAS measuring system works
.
The MIDAS measuring system is based on the double vector-meter method which relies upon the
measurement of the current I
N
through the known reference capacitor C
N
and the measurement of the
current I
X
through the unknown test object C
X
.
Both branches are energized by the built-in HV AC power source (U
Test
) and both currents are
measured by the adjustable high accurate shunts R
X
and R
N
and then digitised. By using IEEE 1394
“fire wire” data bus technology each digitised value is time stamped. With this technology not only the
values but also the time information (phase displacement) between I
N
and I
X
can be measured very
fast and highly accurate.
The digitised data streams are fed into the PC and over the known standard capacitor all other
desired measuring values can now be determined online.