DLRO10 and DLRO10X digital low resistance micro-ohmmeters
Small, lightweight, and portable
Can be used in tight places and reduces the need for extra long leads and two-person operation
Automatically applies forward and reverse currents
Negates the effect of any standing voltages across the sample under test
Detects continuity in potential and current connections
Prevent erroneously high readings due to high resistance contact
About the product
The DLRO10 and DLRO10X digital low resistance micro-ohmmeters bring new standards to low resistance measurement (also known as the Megger ‘Ducter™’ test). Both are fully automatic instruments, selecting the most suitable test current, up to 10 A DC, to measure resistance from 0.1 µΩ to 2000 Ω on one of seven ranges.
If you desire more control over the measurement process, the DLRO10X uses a menu system controlled by a two-axis paddle to allow you to manually select the test current. The DLRO10X also lets you download results in real time and provides on-board storage for later downloads to a PC.
The DLRO10 uses a large, bright 4.5-digit LED display, while the DLRO10X has a large, backlit LCD. Both are visible under all lighting conditions and help reduce errors in reading results.
Both instruments are built into a strong, lightweight case that is equally at home in the field or the laboratory. They are light enough to be worn around the neck, enabling you to take them into areas that were previously too small to access.
Technical specifications
- Data storage and communication
- None
- Max output current (DC)
- 10 A
- Power source
- Battery
- Power source
- Optional mains adapter
- Safety features
- CATIII 600 V
- Safety features
- LED indicators
Troubleshooting
Make sure both C1 and C2 leads are making proper contact with your test specimen. Additionally, you can check for the continuity of those two leads using a multimeter to rule out any potential damage. If these two suggestions fail, it is likely because the current terminals C1 and C2 have become disconnected from the power board, in which case, you will need to send in the instrument for repair.
This is usually the result of the power battery losing charge due to normal ageing or terminal wires loosening. You can replace the battery on-site following the instructions in the User Guide. If that does not fix the issue, wiring issues may necessitate returning to Megger’s repair department.
Non-volatile memory batteries lose charge over time due to natural ageing. Replacing the battery is insufficient, as all calibration settings will have been lost. As such, you need to return the DLRO10 to Megger for recalibration.
The calibration constants have been lost. The DLRO will continue to work, but we can no longer guarantee its accuracy. You need to return the DLRO10X for recalibration.
An error has occurred during the measurement; for example, contact has been lost on one of the probes. Rectify the error and repeat the measurement.
Interpreting test results
Measuring low resistance helps identify resistance elements that have increased above acceptable values. Low resistance measurements prevent long-term damage to existing equipment and minimise energy wasted as heat. This testing reveals any restrictions in current flow that might prevent a machine from generating its full power or allow insufficient current to flow to activate protective devices in the case of a fault.
When evaluating results, it is crucial to pay attention first to repeatability. A good quality low resistance ohmmeter will provide repeatable readings within the accuracy specifications for the instrument. 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 temperature coefficient must be factored into the reading if the ambient temperature deviates from the standard calibration temperature.
Spot readings can be critical in understanding the condition of an electrical system. You can get some idea of the level of the expected measurement based on the system’s data sheet or the supplier’s nameplate. Using this information as a baseline, you can identify and analyse variances. You can also make a comparison with data collected on similar equipment. The data sheet or nameplate on a device should include electrical data relevant to its operation. You can use the voltage, current, and power requirements to estimate the resistance of a circuit and the operating specification to determine the allowed change in a device (for example, with battery straps, connection resistances will change with time). Various national standards provide guidance for periodic test cycles. The temperature of the device will have a strong influence on the expected reading. For example, the data collected on a hot motor will differ from that of a cold reading taken at the time of the motor’s installation. As the motor warms up, the resistance readings will go up. The resistance of copper windings responds to changes in temperature based on the fundamental nature of copper as a material. 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 measurements made with a low resistance ohmmeter against some preset standard (i.e., a spot test), the results should be saved and tracked against past and future measurements. 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 another component will become unsafe and make the necessary repairs. Remember that degradation can be a slow process. Electrical equipment faces 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.
Note: When taking periodic measurements, you should always connect the probes in the same place on the test sample to ensure similar test conditions.