User Manual

GMC-I Messtechnik GmbH 45
11 Measuring Insulation Resistance
Attention!
!
Insulation resistance can only be measured at voltage-
free objects.
11.1 General
Select Measuring Function
Connection
2 pole adapter or test
plug
Note
The test instrument measures the insulation between the
contacts L and PE.
In systems without RCD, N and PE must be separated.
Note
Checking Measurement Cables Before Measurements
Before performing insulation measurement, the test
probes on the measurement cables should be short-cir-
cuited in order to assure that the instrument displays a
value of less than 1 kΩ. In this way, incorrect connection
can be avoided and broken measurement cables can be
detected.
Set Parameters
* Freely adjustable voltage (see section 5.7)
Polarity Selection
* AUTO parameter (see section 5.8)
Breakdown current for Ramp Function
Note
In order to suppress the impact of parallel capacitances
on the DUT when starting a measurement, the ramp
function is only shut down at the preadjusted breakdown
current I
LIM
when a minimum voltage of 5 V is exceeded.
Limit values for Breakdown Voltage
Limit Values for Constant Test Voltage
❑ Test voltage
A test voltage which deviates from nominal voltage, and is usually
lower, can be selected for measurements at sensitive compo-
nents, as well as systems with voltage limiting devices.
❑ Voltage Type
The “U
INS
” rising test voltage function (ramp function) is used to
detect weak points in the insulation, as well as to determine
response voltage for voltage limiting components. After briefly
pressing the ON/START key, test voltage is continuously increased
until specified nominal voltage U
N
is reached. U is the voltage
which is measured at the test probes during and after testing. This
voltage drops to a value of less than 10 V after measurement (see
section entitled “Discharging the Device Under Test”).
Insulation measurement with rising test voltage is ended:
• As soon as specified maximum test voltage U
N
is reached and
the measured value is stable
or
• As soon as specified maximum test voltage is reached, e.g.
after sparkover occurs at breakdown voltage).
Specified maximum test voltage U
N
or any occurring triggering or
breakdown voltage is displayed for U
INS
.
The constant test voltage function offers two options:
R
ISO
R
INS
Voltage type: constant
Test voltage: 15 V/50 V/100 V/250 V/325 V/500 V/1000 V
Voltage type: rising/ramp
Earth leakage resistance:
xxx V*
2-pole measurement (relevant for report generating only):
Measurements between
Lx-PE / N-PE / L+N-PE / Lx-N / Lx-Ly / AUTO*
where x, y = 1, 2, 3
Limit value:
I > I
Limit
U
INS
STOP
low limit:
U
INS
input range:
> 40 V ... < 999 V
upper limit:
Limit value:
R
INS
< Limit Value
U
L
⏐ R
L
U
INS