Megger DLRO10HD User manual

M
DLRO10HD
10 A Digital Low Resistance Ohmmeter
USER GUIDE

2
GSafety Warnings
These safety warnings must be read and understood before the instrument is used.
Whenever possible, circuits should be de-energised before testing.
If it is impossible to de-energise the circuit, (e.g. high voltage batteries cannot be switched off while their connections are tested) the user must be aware
of the dangers. The instrument terminals will become live when connected to the circuit. Therefore when used on hazardous voltages the optional Megger
terminal cover (part number 1002-390) must be used. See the accessories section of this user guide.
Testing inductive circuits can be hazardous:
After testing an inductive load there will be an amount of energy stored in the inductance. This energy is released in the form of a discharge current.
Disconnecting an inductive load while current is still flowing will cause a high voltage arc, which is a danger to both the user and the item under test.
Although the DLRO10HD is not designed as transformer ohmmeter, it is fitted with a test in progress lamp associated with the TEST button, which indicates
that current is flowing in the C1-C2 loop. This lamp and a warning triangle on the LCD will flash at end of a test on an inductive load whilst a discharge
current is still flowing and will stop flashing when the current has decayed to less than 1 mA.
For testing large inductive resistances the current carrying leads should be connected securely to the item under test before starting the test. It is not
recommended that duplex handspikes be used to carry out tests on inductive loads. If inadvertently using the DH4 handspikes on an inductive load, the L1
lamp on the handspikes will flash amber while discharge current flows, thereby duplicating the function of the ‘I’ lamp on the instrument. It is important to
maintain contact until the L1 light stops flashing amber and turns green indicating the end of the test.
This product is not intrinsically safe. Do not use in an explosive atmosphere.
Do not operate the instrument or connect it to any external system if it shows any visible signs of damage or if it has been stored for
prolonged periods in unfavourable conditions.
CAT II -Measurement category II: Equipment
connected between the electrical outlets and
the user’s equipment.
CAT III - Measurement category III:
Equipment connected between the
distribution panel and the electrical outlets.
CAT IV - Measurement category IV:
Equipment connected between the origin
of the low-voltage mains supply and the
distribution panel.

3
Inspection
Before each use of the instrument, visually inspect the instrument case, test leads and connectors to confirm that their condition is good, with no damaged or
broken insulation.
Charging and mains/line operation
In normal circumstances the instrument is completely safe. However, in case of an unforeseen emergency ensure instrument is positioned to allow fast
disconnection of mains/line plug.

4
Contents
Safety warnings 2
General description 5
Application 6
Test modes 7
Warning messages 8
Test techniques and applications 9
General operation 10
Electrical specifications 13
General specifications 14
Accessories 15
Repair and warranty 16
Cleaning
Disconnect the instrument and wipe it with a clean cloth slightly damped
with soapy water or Isopropyl alcohol (IPA).
Symbols used on the instrument
GCaution: Refer to accompanying notes
FHV warning
tEquipment protected throughout by Double or reinforced
Insulation (Class II)
cEquipment complies with current EU Directives
Equipment complies with ‘C tick’ requirements
Do not dispose of in the normal waste stream
xOn/Off position
fFuse
Line power
JBacklight
CContrast
Socket

5
General description
The Megger DLRO10HD enhances Megger’s existing family of 10 Amp DC
low resistance ohmmeters (DLRO10 and DLRO10X). This heavy duty model
combines simplicity of operation with selected high power ranges and
the ability to simultaneously make measurements and charge the battery
from line power. Designed in a rugged case it is equally suited to harsh
environments or factory testing. The unit is IP65 rated with lid closed and
IP54 when operating from battery power. The lid is removable to facilitate
simple connection of test leads. Megger’s DH4 Duplex Handspikes with
1.2 m leads are standard with other lengths and terminations available.
This instrument provides significantly enhanced compliance and is capable of
delivering 10 A while measuring up to 250 mΩ and 1 A while measuring up
to 2.5 Ω. In the high current 10 A modes test current is maintained for up to
60 seconds. The use of a four terminal measurement technique removes the
test lead resistance from the measured value. Additionally, before and during
a test, test lead contact is monitored to reduce the chance of erroneous
readings. The instrument is powered by a rechargeable, sealed lead acid
battery, which permits over one thousand 10 Amp tests to be completed
on a single charge. An auto power off function preserves battery life when
operating from battery power. The battery contains intelligent circuitry,
which prevents damage to the battery from overcharging and charging
under extreme temperatures. A degassing safety vent is provided in the
unlikely event of the battery degassing during charge.
The DLRO10HD provides five test modes each of which is selected via
a rotary switch. Controls are simple and easy to operate in all weather
conditions and with gloved hands operation. The five operating modes
include two automatic modes that sense connection of the probes to
minimise test time and increase productivity. To overcome thermal EMFs
current is passed through the unit under test in both directions and the
resulting resistance averaged. If a user wants to make a series of quick tests
and is not concerned about minor EMF effects, a unidirectional automatic
mode halves the test time by passing current in only one direction. Other
modes include continuous testing with a new result every three seconds and
a unidirectional inductive mode.
A large, clear, backlit LCD display with an oversize five digit main display is
easy to read from a distance.
In common with other members of the DLRO10 family the DLRO10HD
is rated CAT III 300 V. A range of test leads, are available to suit the
application. The instrument is protected against accidental connection to
external voltages up to 600 V DC applied between any pair of the four
terminals for up to 10 seconds. As soon as an external voltage is sensed
measurements are inhibited and the HV warning triangle shows on the LCD
plus a red LED on the keyboard illuminates.

6
Applications
The DLRO10HD measures low resistance values in applications ranging from
railways and aircraft to resistance of components in industry. Any metallic
joint can be measured but users must be aware of measurement limitations
depending on application. For example, if a cable manufacturer plans to
make resistive measurements on a thin wire, a low test current should be
selected to prevent heating the wire thereby changing its resistance.
The DLRO10HD is well suited to measuring thick conductors, bonds and
quality of welding because of its 10 A range for resistance values up to
250 mΩ. Measurements on electric motors and generators will be inductive
and require the user to understand the inductive mode and charging
process before a correct result is achieved. Electromagnetic noise induced
into the leads can interfere with a reading. A noise symbol alerts the user
and prevents a measurement when the instrument detects noise above its
threshold.
When dissimilar metals are joined a thermocouple effect is created. Users
should select a bidirectional mode to ensure cancellation of this effect. The
instrument measures with current flowing in both directions and averages
the result. Typical applications of the DLRO10HD include DC resistance
measurements of:
■Switch and contact breaker resistance
■Busbar and cable joints
■Aircraft frame bonds and static control circuits
■Integrity of welded joints
■Inter-cell connections on battery systems up to 300 V peak
■Quality control of resistive components
■Transformer and motor winding resistance
■Rail and pipe bonds
■Metal alloys, welds and fuse resistance
■Graphite electrodes and other composites
■Wire and cable resistance
■Transmitter aerial and lightning conductor bonding

7
Test modes
Test mode, is selected by a six (including off) positioned rotary selector
switch that activates the following modes:
Normal mode – The test is initiated by pressing the ‘Test’ button after
connecting the test leads to the unit under test. Continuity of all four
connections is checked. Current is applied in both forward and reverse
direction following which the measurement result is displayed. Please note
that in this mode both the current and voltage leads must be connected
across the test sample before the Test button is pressed.
Automatic mode – The test is started as soon as the probes make contact.
Forward and reverse current measurements are made and the average value
is displayed. This mode is ideal when working with the supplied handspikes.
Each time the probes are removed and reconnected to the load another test
will be performed without the need to press the test button.
Automatic unidirectional mode – Here current is applied in one direction
only to speed up the measurement process. However standing EMF’s
setup during the test are ignored so lower accuracy can result. Test starts
automatically when probes are connected. To make another measurement
simply break contact with the test sample and remake contact on next test
sample.
Continuous mode – Allows repeated measurements to be made on the
same sample. Simply connect the test leads and press the test button. The
measurement is updated every three seconds until the circuit is broken.
Please note that in this mode both the current and voltage leads
must be connected across the test sample before the Test button is
pressed.
Inductive mode – When measuring inductive loads it is necessary to wait
for the voltage to stabilise, so the measurement process can take a few
seconds or several minutes. The test leads are firmly connected to the item
to be measured and the ‘Test’ button pressed. The instrument will pass the
selected current through the sample continuously in one direction only. The
instrument will take repetitive readings, which will gradually decrease to the
true value as the voltage stabilises. The operator decides when the result is
stable and presses the ‘Test’ button to terminate the test. When measuring
inductive loads it is essential that the current carrying leads are
securely clamped to the item being tested and that they are not
removed before any stored charge has been discharged at the end
of the test. Failure to comply with these instructions might result in
an arc being produced, which might be dangerous for the instrument
and the operator.
Automatic modes -
bidirectional and
undirectional
current flow
Continuous mode -
test current applied
in both directions,
test repeated at 3
seconds intervals
Normal mode -
test current applied
in both directions
undirectional
current flow
Instrument is off in
this position
Inductive mode –
test current applied
in one direction
only

8
Warning Messages
Noise
Noise in excess of 100 mV 50/60 Hz will activate the noise icon that
will flash and no result will be displayed.
‘C’ & ‘P’ Indicators
A good measurement requires both the current carrying circuit and the
voltage detection circuit to be completed by the unit under test. DLRO10HD
checks for continuity in both C and P circuits. When connectivity is detected,
C 1---2 and P 1---2 indications are displayed in the left bottom sector of the
LCD. If there is poor continuity in either circuit, the “---“ indicators will flash
between C and/or P circuits to indicate a continuity problem.
External Voltage Warning
If external voltage is applied between the terminals and the instrument is
on, the HV warning Fwill flash on the display. This is a warning that the
item under test is live and might be dangerous and testing is disabled. The
HV warning Fmessage will flash if more than 50 V potential difference is
applied between voltage terminals and current terminals. This warning will
not appear if all terminals are at the same high voltage.
Please note - The warning will not operate if the instrument is turned
off.
Discharge Voltage/Current Warning
The HV warning Fand the red HV lamp on the panel will flash if a current
greater than 1 mA is still flowing after an inductive test is completed. This
suggests that the inductive load has been tested and is discharging. Do not
disconnect the current loop while the discharge warning is showing.

9
TEST TECHNIQUES AND APPLICATIONS
TESTING USING DH4 DUPLEX HANDSPIKES
Each handspike is marked with the letter P. This indicates the potential
terminals. These should be the ‘inside’ contacts when making a
measurement. One of the DH4 handspikes is fitted with two lamps marked
L1 and L2 and an extra lead. This lead should be plugged into the 4 mm
socket labelled next to the P2 terminal. These lamps provide information
to the operator that would otherwise only be available on the instrument
display. The meaning of these lamps is described below.
For example, using the DH4 Duplex Handspikes with the DLRO10HD in one
of the AUTO test modes:
1. Press the TEST button on the instrument.
2. Lamp L1 will illuminate a continuous red to indicate contact failure.
3. When all four contacts connect, L1 will extinguish.
4. No lamps will show during the test unless contact fails.
5. Lamp L2 will light a continuous green when current flow has decayed
to less that 1 mA to signal end of test.
6. Removing the probes will extinguish the green L2 (end of test) and
7. Light the red L1 (no contact).
Since your DLRO10HD always ensures good contact before applying the full
test current, there should be no erosion of the contact tips. However, if the
tips become worn or blunted, they can be simply replaced by pulling out the
worn tips and inserting new ones.
TESTING USING DUPLEX HANDSPIKES OR
INDIVIDUAL LEADS
Connect the four leads as shown. In all cases ensure that the potential
probes (P1 & P2) are inside the current (C1 & C2) probes
DH4 Handspikes used with DLRO10HD
Lamp L1 Lamp L2 Meaning
Red Off Inadequate continuity at C
or P contacts
Flashing Red Off Voltage present between
contacts
Off Green Current , 1mA, test
Complete
Off Red Measurement fail

10
GENERAL OPERATION DLRO10HD
Out of the Box
First connect the test leads to their respective measurement terminals. To
simplify lead connection to the DLRO10HD the lid can be removed by lifting
it to approximately 45º from closed position and sliding it to the right.
Connect line power lead if line power is available. If the instrument is to
be operated from the internal battery, ensure that the battery is charged.
Care should be taken to avoid running down the battery to a very low level.
The lead acid battery requires charging at least every three months if the
instrument is not in use for long periods. Charging should be performed in
well, ventilated areas.
The DLRO10HD is switched on at the power and mode selector switch.
On switch on the LCD shows the battery level symbol and, if line power is
applied, the line voltage symbol.
It may be necessary to adjust the display contrast by repetitively pressing the
contrast adjust button. Contrast setting will scroll through its range from
min to max and back to min etc. The backlight ON/OFF button toggles the
state of backlight that will timeout if left on for more than
Test Process
Select the test mode required by rotating the mode selector the respective
icon. The range/current selector is set based on expected resistance value of
the device under test. Alternatively, use the 100μA, 2.5 kΩ range to obtain
an initial magnitude of the resistance and then select the most appropriate
range setting.
The TEST button starts and stops all tests. The two automatic (AUTO) modes
will only show a result on correct connection of test probes and stop current
flow on disconnection.
Measurement terminals
P1
C1
Line input
Line input fuse
Line connected
indicator
Power and mode
selector switch
Contrast adjust
Current flow
indicator
P2
C2
Probe LED indicator
plug/socket
HV warning
indicator
Backlight ON/OFF
Test active indicator
Test START/STOP
Line voltage
connected
Range selector
switch
Battery level
Over temperature
Noise present
Refer to user guide
High voltage
warning