Part 1 of our Loop Resistance Tester comparison series looked at the physical differences between the ExLRT and the legacy LRT tool.  We confirmed that size matters after all – and in this case, smaller is better.

This second article takes a closer look at the improved technology built into the ExLRT, as well as the features designed specifically for MRO end-users in mind.

Designed in partnership with Boeing

The original LRT was revolutionary when it was launched over 20 years ago.  Since then, the expansion of fly-by-wire aircraft has meant that the use of the LRT in MRO environments is growing, yet the design of the tool means it’s no longer fit for purpose.

The ExLRT from MK Test Systems is the result of a close collaboration with The Boeing Company’s EME (Electro Magnetic Effects) team. It’s designed to be an Intrinsically Safe replacement for the LRT, acknowledging of the need for a tool designed for modern industrial use.

We’ve already seen how much smaller and lighter the ExLRT is – you can read more about this in the first article of our comparison series.

The weight alone means the ExLRT can be operated by a single user, providing immediate cost- and time-savings due to the reduced man hours needed.  Besides this obvious advantage, what other features have we built into the tool?

Developed with MRO users in mind

Designed for factory floor as well as field applications. the ExLRT is a tough tool full of features to make testing easier and therefore quicker.

Straight out of the box, the first thing you’ll notice is the large easy-to-read screen.  It’s backlit with a custom LCD display for reading even in direct sunlight. 

Conscious that operators are often taking readings at awkward angles, we’ve added LEDs to the probes and clamps which provide an instant pass/fail result at your fingertips.  The probes also have push button controls which enable operators to accept or re-test much more quickly.

The ExLRT can be set to run in either single test mode or a programmable test sequence.  Simple loop or joint measurements can be taken straight from power-on, whilst more complex test sequences can be downloaded, and the results stored for later upload to a PC.

The ExLRT has been ergonomically designed so it’s not only smaller and lighter, but it’s got a convenient carry handle too.  We’ve developed some additional wearable options to make life even easier – a lightweight harness as well as a belt clip are available to keep the tool hands-free.

exlrt in situ
exlrt in situ

Maintenance made simple

The LRT calibration turnaround time can take up to 6 months, with the average time around 2 months.  We offer a user-based calibration kit which means the ExLRT can be calibrated in around 30 minutes.  Yes, minutes not days. 

The ExLRT can be calibrated onsite by operators in around 30 minutes. Yes, minutes not days.

That’s a huge difference!  Not only is it fast but the process is simple – follow the on-screen instructions to run the test programme using the fixtures provided in the calibration kit.

Is the ExLRT as accurate as the LRT?

The short answer is yes!  The Boeing Company has verified the ExLRT’s resistance measurements as equivalent or superior to the existing LRT – so there are no concerns about loss of data integrity. 

Crucially, the accuracy isn’t affected by dwindling battery life, unlike the LRT.  The ExLRT has replaceable batteries which are removed from the tool for charging.  Not only does this mean the measurements remain accurate throughout the full life of the battery, it also means no downtime whilst the tool is charging.

Other product highlights

The Intrinsic Safety classification of the ExLRT offers obvious safety benefits.  Did you know that not all LRT models are Ex certified, but not only that; by using a tool which is not Intrinsically Safe may mean you’re violating FAA ACO Airworthiness Directives?

The tough polypropylene casing of the ExLRT means it’s protected from dust and water splashing, enabling an IP54 rating (suitable for outdoor use).  It also has an operating temperature between -10°c and +35°c (14 to 95 Fahrenheit).


In short, the ExLRT is a light, modern loop resistance tester designed with end-users in mind.  It’s Intrinsically Safe, can be operated by a single user and is approved by The Boeing Company. 

To learn more about this game-changing loop resistance tester, visit our dedicated product page here.