DLRO10HD and DLRO10HDX digital low resistance ohmmeters
Advanced safety features
It’s protected up to 600 V without blowing a fuse and has a live voltage warning light in case of inadvertent connection to the mains
Battery or mains power supply
Powered from either rechargeable batteries or mains power for continuous testing
Operable in all weather conditions
The heavy duty case is IP54 rated when operational and IP65 when the lid is closed, and the rotary switch controls enable operation with gloved hands
High and low power outputs
Low power to identify problems such as contamination and corrosion, and high power to show weaknesses due to heating
Informacje o produkcie
The heavy duty DLRO10HD and DLRO10HDX digital low resistance ohmmeters can deliver a 10 A current into circuits up to 250 mΩ and 1 A into circuits up to 2.5 Ω. The duration of each test can be up to 60 seconds, reducing the time required for cooling. These units have a high and low output power selection for condition diagnosis.
The DLRO10HD and DLRO10HDX instruments can be powered from their own sealed, rechargeable lead-acid battery or via mains power. This makes them suitable for continuous testing in repetitive use environments, such as production lines. Additionally, they come in a rugged case designed for stable ground and bench operation. They are IP54 rated when operational and IP65 when the lid is closed, which is ideal for working in all weather conditions.
Both units have five test modes: bidirectional (whereby current reversal with averaging cancels thermal EMFs), unidirectional, automatic, continuous, and inductive. You select the desired mode through a simple rotary control on the mode selection rotary switch. These rotary switches are easy to operate, even with gloved hands, and the instruments’ large, clear, backlit LCD makes for easy reading even from a distance.
The DLRO10HDX has some additional abilities over the DLRO10HD. It is rated CAT III 300 V (as long as the optional terminal cover is fitted to the instrument) and comes with onboard memory storage for up to 200 test results. The memory functions: ‘delete’, ‘download to PowerDB’, and ‘recalling test results’ are also accessible via the range selection rotary switch on this model.
Dane techniczne
- Data storage and communication
- None
- Max output current (DC)
- 10 A
- Output type
- Low and high output power
- Power source
- Battery
- Power source
- Mains
- Safety features
- CATIII 300 V
Produkty powiązane
Rozwiązywanie problemów
If the unit does not power up after a full battery charge, it could be due to battery and/or internal components damage. Unfortunately, you must send the instrument back to Megger or an authorised repair centre for evaluation and repair.
Interpretacja wyników pomiarów
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.