The document discusses the importance and applications of low resistance testing using the DLRO2 digital low resistance ohmmeter. It outlines the benefits of such testing, including preventing equipment damage and ensuring reliable electrical connections, while also highlighting various fields of application like power generation, manufacturing, and aircraft maintenance. Key features of the DLRO2, including its measurement capabilities and safety features, are also presented to demonstrate its effectiveness in identifying and diagnosing issues in electrical systems.

1. Brian Hammerschmidt, Megger

2. Principles of Low Resistance Testing
and Applications of the DLRO2
Low Resistance Ohmmeter

3.  What do our end users want?
 What is considered a Low Resistance Test?
 When to measure Low Resistance
 Why measure Low Resistance?
 Benefits of Low Resistance Testing
 DLRO Example Applications
 DLRO2 – Features and Key Characteristics
 Questions
Outline

4.  A Digital Low Resistance
Ohmmeter (DLRO)?
What Do Our End Users Really Want?

5.  Peace of mind
 Reliability
 Cost saving
 Prevention rather than cure
What Do Our End Users Really Want?

6.  Ducter™ testing or low resistance testing (also known as
contact resistance test) measures the resistance of electrical
connections.
 These can be connections between any two conductors,
for example, cable connections, busbar sections, circuit
breakers, aircraft frame bonds, rail and pipeline bonds,
and many more applications.
What is a low resistance test?

7. What is considered to be a low resistance test?

8. What is considered to be a low resistance test?

9. What is considered to be a low resistance test?

10. What is considered to be a low resistance test?

11.  Go/No Go
 Ensure resistance is correct at installation/commissioning
 Condition Monitoring
 Identify unacceptable increase in resistance
 Like Testing
 Ensure ‘like’ elements of a system are of similar resistance
When To Measure Low Resistance?

12.  Identify unacceptable increase in resistance
 Prevent equipment damage / Increase efficiency
 Low resistance path for fault current
 Fault will always take the path of
lowest resistance
 Low resistance path for lightning strike current
 Static electricity dissipation paths
 Drive predictive maintenance
 Spot the increasing resistance and correct
before it becomes a problem
Why Measure Low Resistance?

13.  So what causes an increase in resistance?
 Manufacturing / installation or following a repair
 Bolts not tightened enough – or over tightened
 Poor / rough mating surfaces
 Dirty mating surfaces
 Damage
 Frayed wires / broken strands etc.
 Following long periods of shut down
 Corrosion due to dampness
 Chemical attack
Why Measure Low Resistance

14.  So what causes increase in resistance?
 In service
 Environmental and chemical attack
 Even air will oxidize
 Moisture ingress
 Oil and salt will degrade connections
even more rapidly.
 Chemical corrosion can attack the
mating surfaces
 Electrical stresses
 Over voltages or impulses
Why Measure Low Resistance?

15.  So what causes increase in resistance?
 Mechanical stress
 Vibration, impact, start / stop
 Metal fatigue
 Equipment heat up and cool down cycles
 Poor solder joints
Why Measure Low Resistance?

16.  Identify unacceptable increase in resistance
 Ensure low resistance path for fault current
 Ensure low resistance path for lightning strike current
 Ensure dissipation paths for static electricity
1. Protect people
2. Save energy
3. Prevent fires
4. Protect equipment, buildings, wind turbines, etc.
5. Ensure product quality
Five benefits of low resistance testing

17. DLRO EXAMPLE
APPLICATIONS

18.  Testing elements of resistance
 Checking each point of connection
Measuring Components of a System

19. Using Resistance To Check Torque

20. Typical Faults Prevented

21. Typical Faults Prevented

22.  During electrical manufacturing processes
 Testing switches, connectors, relays and circuit breakers
 To ensure contact resistance is within specified values.
 Cable resistance
 Too low means too much copper in cable (higher costs),
too high means not enough copper (the cables’ current
carrying capacity compromised)
 Motors – Including Railway traction motors
 To determine heat rise under load, measure winding
resistance, check for short circuits or open circuits.
 Generators
 To determine heat rise under load, measure winding
resistance, check for short circuits or open circuits.
DLRO example applications

23.  During electrical manufacturing processes:
 Fuses
 To ensure resistance is within specified values.
 Cable looms
 Checking bonding and interconnections when
installing in equipment, racks etc.
 UPS / Car batteries
 Carrier to plate weld resistance, High resistance
indicates poor weld quality that will restrict battery’s
ability to carry current.
 Electronics
 PCB track resistance, component testing
DLRO example applications

24.  Industrial / Manufacturing Plant maintenance
 Power system
 Motor / generator
 Process control plant
 University / Colleges
 Research applications
 Mining Industry
 Underground supply, pumps, lighting etc
DLRO example applications

25.  Aircraft assembly and maintenance
 Main frame electrical and mechanical bonds –
to ensure a stable “ground plan” to protect
aircraft from static electricity and
lightning strikes.
 Static wick bonding
 Antenna bonds
 Control linkage bonding
 Battery connection and interconnection
 Integrity of structure and exhaust system
 Metallic coating resistance
DLRO example applications

26.  Aluminium refineries
 Graphite electrodes – to verify density
 Ship building or any metal structures
 Weld quality – measure at regular intervals along weld length
looking for uniformity.
 Installed equipment bonds – to steel structure / hull.
 Raw material processing, e.g. cement plants
 Power carrying elements – installation and maintenance
 Ground bonds - cement is corrosive
 Automotive industry – car, van, commercial vehicle
 Cable leads in robot spot welders work-harden through flexing
causing strands to break. Results in poor weld quality.
DLRO example applications

27.  Power Generation and Distribution
 Bus bars – lap joint tests to maintain low resistance, and hence
maintaining efficiency and reducing likely hood of fire.
 Cable joints – including overhead lines. High impedance joint can
explode.
 Fuses – connections
 Uninterruptible Power Supply (UPS)
 Battery straps – quality of connections. Preventing potential of
fire and failure to operate
 Carrier to plate weld resistance – High resistance indicates poor
weld quality that will restrict battery’s ability to carry current.
 Military vehicles – Trucks, tanks etc.
 Installed equipment such as radio equipment - ground bonding
to vehicle chassis.
DLRO example applications

28.  Buildings – wiring, lightning protection bonds
 Various bonds, both for power distribution and earth
grounding – check for step and touch voltage safety in fault
condition.
 Conduit continuity – metal conduit, detect corroded or loose
threads etc.
 Wind turbines – manufacturing and installation
 Lightning protection – wing tip to base, or component parts
in manufacture. Long test leads available for this
application.
 Earth ground bonds – various
DLRO example applications

29.  Mobile Phone Companies
 Car Manufacturers
 Aircraft Manufacturers and Airlines
 UPS Installers
 Ship Builders
 Oil Rigs
 Power Generation and
Distribution Companies
 Chemical Plants
 Refineries
 Mines
 Railways
 Telecommunications Companies
General List of Industries

30.  Better than insurance…
Insurance picks up the pieces when
things go wrong…
….Low resistance testing prevents
it from going wrong
The low down of low resistance testing

31.  Ducter™ Low Resistance Ohmmeter
 2A output
 Up to 2000 Ω with 1 µΩ resolution
 Hand held
 Easy to use
 Reliable, repeatable measurements
 Rugged, molded case
 Rechargeable batteries
 Color display
The new DLRO2
Look out for these

32.  DLRO2
 BT51
 DLRO10HD
 DLRO10HDX
 DLRO10
 DLRO10X
DLRO2 – where it will fit?

33.  Testing at 10A
 Higher current provides better ability to heat and expose weaknesses
 DLRO2 maximum power output = 4 W
 DLRO10HD maximum power output = 25 W
Difference between testing at 2A and 10A
DLRO10HD

34. Difference between testing at 2A and 10A
 Testing at 10A
 Ability to select both very low currents and higher
currents like 10A provide an element of diagnosis with
the ability to find issues such as contamination and
current carrying weaknesses
 Large format of 10A testers allows use of much larger
batteries and therefore improved battery life
DLRO10
DLRO10X

35.  Testing at 2A
 A 1 A or 2 A four wire measurement will still find issues not possible with
a 200mA continuity test
 High enough current to provide 1 µΩ measurement
resolution
 Enables a smaller, lighter and hand held instrument
 Easier to carry, store and transport
 Less weight improves safety when working at height
 Less battery capacity required, hence the convenience
of using 6 x AA batteries
 The small handheld format means a more cost
effective solution
Difference between testing at 2A and 10A

36.  Truly hand held, high performance
 Tool box sized, take anywhere solution
 Simple to use
 Current DLRO10 range offers:
 Hang round neck
 Transport case style
 Hand held
DLRO2 – Why?

37. • Three main test modes
1. Normal resistance µΩ ≤2A
2. Long test leads mΩ ≤1A
3. Inductive resistance µΩ ≤1A
Test current options
 Five current outputs
 Uni-direction or Bi-direction
Test options
 TEST button start or AUTO continuity start
 Single test or Continuously repeated
 Inductive manual stop or auto stop
Display option
 Forward and reverse result or Previous two results
DLRO2 - Easy to use

38.  Easy operation - no hidden functions
 CATIII 600V / CATIV 300V safety
 IP54 for outdoor use
 High noise immunity
 Active protection (>600V without blowing a fuse)
 Fuse protected to 1000V
 Inductive mode with new auto stop feature
 Long test lead mode
 New ‘Difference meter’
 User FW updates via USB stick
DLRO2 key features

39. 1. Long test lead / mΩ test mode
 Separate, easy to select test mode that optimizes the
instrument for use with very long test leads
 Only tests at 1 A with positive only output tolerance
to comply with 1A minimum current requirements for
wind turbine and aerospace requirements
 Can apply 1A in a total resistance of up to 3 Ω,
allowing potentially over 150m (492 feet) of test
cable to be used
DLRO2 – Unique features

40.  New cable reels for DLRO2
Lower cost, lighter weight
 Lower weight = safer
DLRO10 performing test
 Long test lead / mΩ test mode
applications
 Testing lightning protection on
wind turbines
 Testing aircraft bonding and
resistance between lightning
receptors
 Subsea cable laying - testing
safety ground connections
DLRO2 – Unique features

41. 2. Difference meter
 A plus and minus percentage scale
along the top of the display
 First measurement becomes a 0% reference
 Each subsequent measurement will cause a pointer to move to indicate
the % difference from that reference
 Each measurement leaves a blue marker on the scale allowing an easy
indication of the % difference
 Noisy measurements leave a red marker
 Reference can be reset using yellow tick button
 Hint: If not required the difference meter can be switched off in settings,
then the main measurement digits become larger
DLRO2 – Unique features

42.  These small differences in resistance
would not be detected using a 200
mA continuity test
DLRO2 – Unique features
 Difference meter applications
 Used when testing a lot of similar
connections such as bus bar joints,
cable lugs, crimps etc.
 Easy to identify connections with
slightly higher measurements that
could indicate a latent fault
 Small increases in resistance in a
joint can be indication of a future
major fault or even fire

43. 3. AUTO STOP function on inductive test mode
 Instrument will automatically stop test and hold final value
as soon as the measurement has become stable
(i.e. the inductance has fully charged)
 Feature can be turned on and off using a soft key toggle option
DLRO2 – Unique features

44.  Hint: The DLRO2 can also
display three test results at the
same time. Ideal for comparing
the resistance in three phase
applications e.g. stator windings
DLRO2 – Unique features
 Inductive AUTO STOP applications
 Great for testing small/ medium
sized motors or transformers in
production environment
 Can start the test and not have to
watch for resistance measurement to
stabilise as the inductance becomes
charged, then stop the test

45.  Protected to 600V live voltage without blowing a fuse
 Like the popular DLRO10 range, the DLRO2 actively protects itself against
accidental connection to live voltage
 The DLRO2 will warn of live voltage and inhibit testing
 Protection between all test terminals
 From user guide:
DLRO2 – Unique features

46.  Hint: The DLRO CATIV 300V rating is
also valid up to a 3000m altitude, rather
than the standard 2000m requirement of
IEC EN 61010
 This makes the DLRO2 safer to use in high
altitude locations
DLRO2 – Unique features
 600V active protection applications
 Ideal for working in industrial locations
 Helps to prevent time wasted replacing
blown fuses
 Helps to prevent time wasted waiting for
expensive instrument repairs to be carried
out

47.  Standard fitted AA rechargeable NiMH
batteries may be changed to Alkaline
 Forgetting to charge the DLRO2 will not stop you
from testing. Simply change the 6 x AA
rechargeable batteries to alkaline and carry on
testing
 In settings menu simply change the battery type
from NiMH to Alkaline to inhibit charging and
optimise the DLRO2 performance to suit alkaline
batteries
 Additional protection prevents damage if a user
inadvertently tries to charge the alkaline
batteries
DLRO2 – Distinctive features

48.  IP54 rated
 5 = “Ingress of dust is not entirely prevented, but it
must not enter in sufficient quantity to interfere with
the satisfactory operation of the equipment;
complete protection against contact.”
 4 = “Water splashing against the enclosure from any
direction shall have no harmful effect.”
 Hint: If you see a competitor proudly claiming IP40
remember this:
 The first digit 4 means protection against objects
>1mm, e.g. most wires, screws, etc.
 The second digit 0 means there is NO protection at all
for water
DLRO2 – Distinctive features

49.  Display settings
 The yellow display may be changed to white in the
instrument settings
 Increased contrast is ideal for reading in direct sunlight
 The difference meter may be turned off
 With difference meter switch off, the main display digits
become larger – making it easier to read
DLRO2 – Other useful features

50. DLRO2
High performance in a
hand held instrument

51. Questions?
Email Christina Spearman christina.spearman@transcat.com
Transcat: 800-828-1470
www.transcat.com
For related product information, go to:
www.transcat.com/brand/megger-store