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Testing Cables and Connectors in Medical Equipment
By Margaret Bishop, Ph.D., CAMI Research, Inc.
demand for higher-capacity devices within the same external envelope is driving electrical design toward increasingly compact solutions, especially in medical electronics. This includes com-
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being used in more board-to-board and board-to- cable interfaces. With narrow pitch comes a higher probability of shorts. Smaller-gauge wires are more difficult to insert. Combined with well-docu- mented contact locking lance issues, there is a greater chance of continuity breaks, especially when connector and terminal position assurance devices are neither features of the design nor of the chosen connector. Some high-performance, high-density board-to-
board connectors incorporate a “floating” design that mechanically absorbs alignment errors, reducing stress and solder cracking. These floating contact systems can move in two lateral axes by as much as 0.024 in. (0.6 mm). During the operation and life of the device, there is a probability that this floating contact may move. How can continuity be verified across the full range of available motion? Testing continuity and high potential (hipot)
with multiconductor cable testers is an essential part of the workflow. Thorough testing prior to and after installation reduces the likelihood of device failure, including catastrophic events, such as fire. It is simply not sufficient to rely on “glow-wire” specifications to prevent fires.
Continuity Test The traditional, basic continuity test checks
Figure 1: Test fixtures accommodate connectors of different types and pitches.
bining signal and power lines within a single connec- tor and reducing the pitch of board connectors. Consequently, micro-pitch connectors are
for opens and shorts at an instant in time only. The limitation of this approach is that the result is only true for the test object as it was presented in the physical location and orientation at that instant. Consider a connectorized cable. If such a test
was performed and yielded a pass, it cannot be assumed that the same would hold true if the cable were moved to other points throughout its full range of motion. Broken wires, cold solder joints and bad crimps can all cause intermittent failure.
Figure 2: Screenshot from CableEye test system with TE PTL connectors.
in a frustrating equipment failure; at worst, in a major malfunction or life-threatening catastrophe, such as a fire or loss of life support. To check continuity thoroughly, an enhanced
test should be performed that scans for opens and shorts, as well as intermittence and miswire errors. These can be measured quickly across all conductors and in a manner that clearly identifies the type of error compared with a desired “golden”
Continued on next page The danger is that companies relying on the
traditional test are at risk of installing defective cables in their equipment. At best, this could result
May, 2018
See at NEPCON China, Booth 1A32
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