Electrical Tester online
May 2009
The low down on resistance

The low down on resistance

01 May 2009

Clive Pink – Product manager

Low resistance measurements have a huge range of applications, from verifying busbar joints and evaluating the effectiveness of bonding in earth systems to checking the resistance of cables and components. Measuring low resistances accurately and reliably, however, presents a number of challenges.

For example, in some applications, such as the testing of welds and bonding, high test currents are needed to obtain reliable results, whereas in other applications, such as measuring the resistance of cables, high test currents must be avoided because the heat they generate will alter the resistance of the item under test.

Further, low resistance test sets need to be readily portable yet rugged, as they are frequently used in demanding on-site situations. To meet these requirements, Megger has recently introduced the DLRO10HD, the latest addition to its successful family of portable digital low resistance ohmmeters.

Equally at home in the laboratory, the workshop or in the field, on the bench or on the ground, the DLRO10HD features an internal rechargeable battery and can also operate from a mains supply, even if the battery is fully discharged.

This new test set is built into a tough but easy-to-carry case that provides an IP65 ingress protection rating when closed and an IP54 rating when the instrument is in use and operating from battery power. It is rated CATIII, 300 V in line with IEC61010, and provides 0.1 μΩ resolution with 0.2% basic accuracy.

To further enhance its versatility, the DLRO10HD features high compliance and offers user-select-able high (10 A for loads up to 250 mΩ) and low (1 A for loads up to 2.5 Ω) current operating modes. A 250 mW power limit feature, with optional override, is also provided for applications where it is desirable to avoid heating the item under test.

The instrument offers a choice of five test modes. In normal mode, the test is initiated by pressing the “test” button. The instrument verifies continuity of all four connections, and then applies the test current in both forward and reverse directions before displaying the result. In automatic mode, the test starts as soon as the probes make contact with the item under test.

Automatic unidirectional mode is the same as automatic mode, but the test current is applied in one direction only. This reduces the testing time, but thermal EMFs from contact between dissimilar metals may reduce the accuracy of the results.

Continuous mode makes repeated measurements at three-second intervals on the same sample, while inductive mode is, as the name suggests, optimised for tests on motors, transformers and other inductive loads.

To see a video of how tough the DLR10HD is on YouTube® click here