Measured Value Quality; Partial Resistances R (R_Iso_Pos) And R; (R_Iso_Neg) - Bender ISOMETER iso175 Manual

Function
The present duration of an individual insulation measurement is output by the measured value Isolation:
Time_elapsed_since_last_measurement. At the beginning of each new insulation measurement this value is
automatically reset to 0 s.
Due to the then following internal statistical filtering and averaging of the individual measured values, the
insulation resistance measured value is only available at the device interface with a delay (after up to 12
individual measurements).
When the fast start measurement is activated (Power-On profile "Standard with fast startup" or "High Capacity
with fast startup"), the insulation resistance measured values (R_iso_original, R_iso_corrected and R_iso_neg,
R_iso_pos) satisfy the specified tolerance as soon as the status signals R_iso_status = 0xFE.
When the fast start measurement is deactivated (Power-On profile "Standard", "High Capacity", "Disturbed",
"Service"), the specified tolerance is met only after 12 individual measured values have been obtained in the
status R_iso_status = 0xFE.
For a rough estimate of the duration of an individual measurement, the following approximation formula
can be used:
t ~ 5 * R
II R
i iso
An insulation resistance R_iso_corrected is made available at the interface, and from which the currently
valid "tolerance value" (set tolerance percentage times measured value) is subtracted. This ensures that this
measured value never exceeds the actually present insulation resistance. The following example serves to
illustrate this device function:
Rf = 1 M , R_iso_original (measured) = e. g. 1.05 M → tolerance ±12 %
R_iso_corrected = 1.05 M – 1.05 M * 0.12 = 924 k
4.3.2

Measured value quality

For every insulation resistance value (R_iso_original / R_iso_corrected) there is a quality information (Quality)
which reflects the reliability of the measured insulation resistance value.
In a stable HV system without voltage fluctuations the quality is always between 90 % and 100 %.
When the HV voltage is instable, the currently performed measurement may be aborted. The obtained
measured values are characterised internally as invalid and are discarded by the statistical filtering. In the event
that such results occur too often over a short period of time, the statistical averaging is impaired, which is
signalled by the quality information.
4.3.3 Partial resistances R
The overall insulation resistance corresponds to the parallel connection of the two partial resistances of R
and R , in each case to earth.
F-
The two partial resistances R_iso_pos (R
resistance using the residual voltage (voltage difference U
is needed, if not, the two partial resistances are output as SNV.
12 iso175_D00415_01_M_XXEN/11.2023
* C
e
(R_iso_pos) and R
F+
) and R_iso_neg (R
F+

(R_iso_neg)

F-
) are calculated from the overall insulation
F-
and U ). For this an HV voltage of at least 100 V
RF+ RF-
F+