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MK Test Systems

Complete Electronics and Software Design of the ExLRT Loop Resistance Tester


A result of a long-term project between The Boeing Company and MK Test Systems, the ExLRT is an intrinsically safe loop resistance tester.

Loop resistance testers are commonly used by aerospace MROs (Maintenance, Repair & Overhaul) to test earth bond resistances. The existing tools available on the market aren’t intrinsically safe so can possibly generate sparks. In an MRO environment, the aircraft’s fuel tanks are potentially explosive chambers just waiting to be set off. While this might be fun to watch in the movies, in real life this could be catastrophic. This is why Intrinsic Safety is paramount, but was lacking.


Boeing challenged MK Test Systems to create an Intrinsically Safe version of their existing BLRT loop resistance tester. The finished product went further than that by meeting or surpassing all the performance requirements of the existing unit. It is a tool that is also easier to use and offers more powerful features. The device must perform measurements accurately and correctly; the performance requirements are as demanding as the intrinsic safety requirements.

The need to balance these two often contradictory needs presented many interesting challenges during the design of the ExLRT, such as creating customised couplers, using very low currents and high inductances to prevent sparking, but still provide a sub-milliohm level of accuracy. Mutech’s expert understanding of Intrinsic Safety systems enabled MK Test Systems to develop a tool which achieved all the criteria required by Boeing.


This was a complex project and has resulted in a specialised tool suitable for today’s testing environments and quality standards. MK Test Systems and Mutech worked together to develop this next-generation loop resistance testing tool by collaboratively addressing these problems.


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