May, 2018 Continued from previous page


or “master” cable design. Figure 2 (previous page) is a


screenshot from CAMI’s CableEye® test system that illustrates a multi- conductor cable with two faults, an open (yellow) and a miswire (yellow- red stripe). In this particular case, pin four has been wired to pin four, which is correct, but without the specified in-line component (a diode), causing a miswire to be flagged. Correctly wired sockets and


plugs will also show up as miswire faults if they have been connected in something other than the specified ori- entation. Knowledge of the type and position of error provides useful feed- back to process improvement engi- neers and quality control personnel. Unusual connectors, such as


connectorized catheters, are easy to incorporate into these tester proce- dures as well. Connector pins that are not fully seated cause intermit- tent opens, while conductive debris is often the source of intermittent shorts, especially in micro-pitch con- nectors.


These faults might cause inter-


mittent power disruption to a motor that may result in damage, or signal a solenoid to switch the wrong valve or the right valve at the wrong time, perhaps delivering the wrong dosage to a patient. Testing for intermittent faults is


very easy. An operator, or a fixture, such as a design verification “shake” table, flexes the cable while a continu- ous stream of test pulses sweep through the full set of test points. Errors are detected and identi-


fied only when a test pulse coincides with an intermittent event, which may be fleeting. Because of this, the test engineer adjusts the cycle fre- quency to capture the most fleeting, random events. The intermittence test in Figure 3 shows that 1.4 per- cent of the 434 test cycles, at 100 ms/cycle, coincided with an intermit- tent event. Clearly, the intermittent fault was hard to trigger, or was so brief that events tended to occur between the test pulses. It takes only one detected event


to fail the cable, ensuring that only high-quality and high-reliability prod- ucts enter the market. This example is a multiconductor test. PC-based cable testers, such as CAMI’s CableEye, can perform 64 test point intermittence testing as fast as 11 ms/cycle over any duration. With this speed and efficiency, and given that there is no additional set up time as opposed to a standard continuity test, there is no reason to exclude a check for intermittent errors. The same test process can be


used to verify board-to-board connec- tors with floating designs. The inter- mittence test is performed while the connector is moved through its entire adjustment range. Design verification data gathered by Samtec suggests that between 2 and 9 lb (0.9 and 4.1 kg) of force is required to move these particular connectors to their maxi- mum range. The motion could be applied manually or through a motor- ized jig for improved repeatability.


High-Voltage Tests Insulation integrity is verified


with high-voltage (HV) tests and can be carried out with AC or DC volt- ages. In either case, the test calls for the applied voltage to far exceed the


Figure 3: Screenshot of an intermittence test on a cable with Samtec 0.03 in. (0.8 mm) pitch Tiger Eye™ connectors and discrete wires.


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Page 75 Testing Cables and Connectors in Medical Equipment


specified operating voltage. For safe- ty reasons, HV tests are applied only after successful completion of conti- nuity testing. Testers, such as the CableEye


HVX series, perform both categories of tests and can be programmed to automatically and seamlessly switch from one to the other. These HV tests consist of checking the dielectric with- stand voltage (DWV) and the insula- tion resistance (IR) to reveal design and manufacturing faults that include insulation pinholes and the presence of gap-bridging moisture. A passing device will be proven


to have insulation capable of protect- ing the end user even during power


Continued on page 80


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