Megger DLRO10HD Instruction Manual

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DLRO10HD

10 A Digital Low Resistance Ohmmeter

USER GUIDE

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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 custom Megger
DH7 test leads must be used

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 visable signs of damage or if it has been stored for
prolonged periods in unfavourable conditions.

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 4

Application 5

Test modes 6

Warning messages 7

Test techniques and applications 8

General operation 9

Electrical specifications 11

General specifications 12

Accessories 13

Repair and warranty 14

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

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 up to 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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APPLICATION

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