Megger DLRO10HD Operating Manual

DLRO10HD
10 A Digital Low Resistance Ohmmeter

USER GUIDE

M

G Safety 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.

Measurement category II: Equipment

CAT II -

connected between the electrical outlets and
the user’s equipment.

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 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.

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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.

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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

G Caution: Refer to accompanying notes
F HV warning
t Equipment protected throughout by Double or reinforced

Insulation (Class II)

c Equipment complies with current EU Directives

Equipment complies with ‘C tick’ requirements

Do not dispose of in the normal waste stream

x On/Off position
f Fuse

Line power

J Backlight
C Contrast

Socket

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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.

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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

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