DLRO100 series of digital low resistance micro-ohmmeters
Small, lightweight, and portable
Weighing only 7.9 kg, the battery-operated DLRO100 series can be used in almost any location
Advanced design for safe operation
Rated at CAT IV 600 V, and IP54 (lid open) for protection against dust and moisture whilst testing, the DualGround™ option for testing circuit breakers adds additional safety and convenience
High noise immunity
For stable readings in electrically noisy environments, which aids in comparing or trending results over time. From testing in industrial applications all the way to 765 kV substations, the DLRO100 will provide accurate consistent results day in and day out
Smooth DC output for circuit breaker testing
Reduce circuit breakers unexpectedly tripping during low resistance measurements with negligible ripple in the DC output
About the product
The DLRO100 series of digital low resistance micro-ohmmeters are portable, lightweight instruments that can deliver a test current of 100 A. They can be supplied with internal rechargeable Li-ion batteries that provide sufficient power for up to 200 manual/automatic tests on a single charge. This degree of autonomy makes it easy for you to perform high current low resistance testing in almost any location, including areas without access to a mains power supply.
To ensure dependable operation even in the most demanding environments, the DLRO100 instruments use novel circuitry that gives high noise immunity and guarantees stable readings. For physical protection, they feature enclosures with an IP54 ingress protection rating even when the lid is open and testing is in progress.
Operator safety in adverse conditions is assured by a CAT IV 600 V safety rating in line with IEC 61010. With an optional DC clamp, dual ground operation is also supported. DualGround™ greatly enhances safety when working in substations and similar environments by allowing tests to be carried out with both sides of the equipment under test grounded.
DLRO100 instruments have a wide range of applications, including checking the resistance of busbar and cable joints, measuring wire and cable resistance, and verifying lightning conductor bonding. They are also well suited for testing switchgear and circuit breakers during manufacture and in the field, and they offer a smooth DC output that is particularly valuable for circuit breaker tests.
Instruments in the DLRO100 series have a measuring range of 0.1 µΩ to 1.999 Ω with a resolution of 0.1 µΩ. Results are shown on a large LCD panel and, depending on the model, can also be stored in a large capacity internal memory for later access via the display or downloading via a USB drive. Versions are also available with support for remote operation, Bluetooth connectivity, and asset/result tagging.
There are three main models in the series, each have battery and mains power supply:
- DLRO100EB is a battery and mains operated unit.
- DLRO100XB is a battery and mains operated unit. DualGround capability with optimal clamp and internal memory storage with USB drive download.
- DLRO100HB is a battery and mains operated unit. DualGround capability with optimal clamp and internal memory storage with USB drive download. Remote control, asset tagging and Bluetooth®.
Technical specifications
- Data storage and communication
- Bluetooth
- Data storage and communication
- USB
- Max output current (DC)
- 110 A
- Output type
- Smooth DC
- Power source
- Battery
- Power source
- Mains
- Safety features
- DualGround™
- Safety features
- LED indicators
Related products
Troubleshooting
When the test is in process, this LED remains lit until the DLRO no longer detects voltage on the lead set. If this is lit when the instrument is not conducting a test, then it is indicating there is a fault. DO NOT USE THE INSTRUMENT if this happens. Do not attempt to repair the instrument. Please return the instrument to the Megger Repair Department for repair.
If the internal temperature of the instrument exceeds a safe level, the test will be aborted and indicated on the screen. The temperature must drop before testing can be continued.
This indicates that there is noise on the system. If possible, earth or ground the asset under test to help reduce the noise.
Interpreting test results
Measuring low resistance helps identify resistive elements that have increased above acceptable values. Resistive elements, including weld joints, electrical crimps, terminations, and current-carrying contacts, are unavoidable in constructing an electrical asset or system. These are points in an electrical circuit where it is desired that the resistance is as low as possible. Low resistance measurements are required to prevent long-term damage to existing equipment and minimise energy wasted as heat. This testing reveals impeded current flow that may prevent a machine from generating its full power or protective devices from activating in the case of a fault.
When evaluating results, it is vital first to pay attention to repeatability. A good quality low resistance ohmmeter will provide repeatable readings within its accuracy specifications. A typical accuracy specification is ±0.2 % of reading, ±2 LSD (least significant digit). For a reading of 1500.0, this accuracy specification allows a variance of ±3.2 (0.2 % x 1500 = 3; 2 LSD = 0.2). Additionally, the result must be compensated by an appropriate temperature coefficient if the ambient temperature deviates from the standard calibration temperature.
Spot readings can be instrumental in understanding the condition of an electrical system. You should have some idea of the level of the expected measurement based on the system’s data sheet or the supplier’s nameplate. Variances can then be identified and analysed using this information as a baseline. You can also make a comparison with data collected on similar equipment.
A device’s data sheet or nameplate should include electrical data relevant to its operation. You can use the voltage, current, and power requirements to estimate the resistance of a circuit. Meanwhile, the operating specification can be used to determine the allowed change in a device (for example, with battery straps, connection resistances will change with time).
The temperature of the device has a strong influence on the expected reading. For example, the data collected on a hot motor will differ from a cold reading taken at the time of its installation. As a motor warms up, its resistance readings will go up. The resistance of copper windings responds to temperature changes based on copper’s positive temperature coefficient. Using the nameplate data for a motor, you can estimate the expected percentage change in resistance due to temperature using Table 1 for copper windings or the equation on which it is based. Different materials will have different temperature coefficients. As a result, the temperature correction equation will vary depending on the material being tested.
Temp ºC (ºF) | Resistance μΩ | % Change |
---|---|---|
-40 (-40) | 764.2 | -23.6 |
32 (0) | 921.5 | -7.8 |
68 (20) | 1000.0 | 0.0 |
104 (40) | 1078.6 | 7.9 |
140 (60) | 1157.2 | 15.7 |
176 (80) | 1235.8 | 23.6 |
212 (100) | 1314.3 | 31.4 |
221 (105) | 1334.0 | 33.4 |
R(end of test)/R(start of test) = (234.5 + T(end of test))/(234.5 + T(start of test)
In addition to comparing low resistance measurements against some pre-set standard (spot test), the results should be tracked against previous measurements and saved for future trending. Logging measurements on standard forms with the data registered in a central database will improve the efficiency of the test operation. You can review previous test data and then determine on-site conditions. Developing a trend of readings helps you better predict when a joint, weld, connection, or other components will become unsafe so you can make the necessary repairs.
Remember that degradation can be a slow process. Electrical equipment is subject to mechanical operations or thermal cycles that can fatigue the leads, contacts, and bond connections. These components can also be exposed to chemical attacks from either the atmosphere or man-made situations. Periodic tests and recording of the results will provide a database of values that can be used to develop resistance trends. Various national standards provide guidance for test cycles.
Note: When taking periodic measurements, you should always connect the probes in the same place on the test sample to ensure similar test conditions.