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3.2. AC/dC VoLtAGE MEASUrEMENt
Turning the switch to any insulation measurement position (U-FIXED, U-VAR, U-RAMP, or U-STEP) sets the instrument to AC/
DC voltage measurement. The voltage between the input terminals is measured at all times and indicated as RMS value on the
display unit: Input Voltage. Switching between AC and DC mode is automatic.
In the case of an AC signal, the instrument measures the frequency. It also measures the residual DC current between the terminals
of the instrument. This measurement is used to evaluate its impact on the insulation measurement about to be made.
The insulation measurements cannot be started if there is an excessively high external voltage (>25V
rms
) on the terminals.
FIXED VOLTAGE
500 V
Input voltage
Frequency
Input current
Date 2011.05.23
230 V AC
50.0 Hz
24.6 nA
Time 10:31
-- V
1000 V
BURN
The blinking
symbol then appears next to the measured external voltage value.
The only errors possible in a voltage measurement are:
The frequency is outside the measurement range (see §8.2.1)
The voltage is outside the measurement range (see §8.2.1).
3.3. INSULAtIoN MEASUrEMENt
%
The insulation measurement is made on an object that is not live.
This measurement varies greatly with the temperature and the relative humidity. It is therefore
essential to measure them and to record them with the insulation value.
The ambient temperature can be entered in the instrument as a parameter, making it possible
to refer the measured insulation resistance value to a reference temperature (see § 4.1).
The value of the test voltage is generally twice the voltage at which the object to be tested is used, unless a standard stipulates
otherwise.
For example, for a motor that operates on 230V mains, the test will be performed at 500V.
3.3.1. dESCrIPtIoN of tHE MEASUrEMENt PrINCIPLE
The instrument generates a DC test voltage equal to the chosen nominal voltage U
N
between the + and - terminals. More precisely,
the value of this voltage depends on the resistance to be measured (see the curves of §8.2.3). The instrument measures the
voltage and the current between the two terminals and from them deduces R=V/I.
The instrument measures the external voltage present on the terminals. It can make the measurement if the peak voltage is less
than 0.4U
N
. Beyond this value, it reports an error and does not make the measurement.
