Nine-Sigma Leak Test of Medical Device Disposable Tubing


When a company makes 6 Million medical device disposable for direct patient contact, Six-Sigma is not enough.

One of the largest medical device companies turned to Cyth Systems to develop leak testing equipment which would test accurately enough and quickly enough to move from random sampling to 100% testing.

One of the most common problems with plastic tubing is its tendency to have either a leak or occlusion immediately after manufacturing. The problem can arise from a bad component or from improper assembly.

Challenge The customer required large quantities of tests performed without operator interaction, a more affordable, compact, and rapid test solution. Since the leaks would be as small as 0.1 sccm, the device required high resolution and precision. The system must use a touchscreen to operate each controller and show a statistical dashboard view of the throughput of the cell on a large flat screen.

Solution Cyth Systems was able to achieve this goal in a compact design. The design resulted in one controller with the ability to control 12 test fixtures. Each test fixture is connected to Circaflex with a single cable. The FPGA component of Circaflex handles all of the input and output interaction, while the test sequence for each test-head was run in its own thread on the real-time OS. The interaction with the large screen was handled through the Microsoft Windows® interface of Circaflex.

Cyth not only performed the electrical and software components of this test system, but also designed and fabricated all of the mechanical fixturing for the controller and the test heads.

Each of the testing fixtures contains:

  • Pneumatic valves

  • Pneumatic linear actuators

  • SICK proximity sensors

  • Hall effect sensors

  • Pressure transducers

  • Pressure regulators

  • Magnetic Reed Switches

  • Emergency Stop Button

  • Custom enclosures and face plates

Figure 2. Controller for 12 testing fixtures

Figure 1. Production photo of test fixtures and controller

Test Time Of all of the requirements, the strictest was the time to test each set of tubing. There was a requirement to have each set test in 10 seconds. This included filling, settling, testing for leak, and testing for occlusions as well as all of the physical interaction with the part. Standard leak testing hardware could meet the test times for the fill, settle, leak, and occlusion test but that did not include any time for interaction with the parts at all. This would require much more interaction from an operator and was not acceptable to the client.

Testing for Leakage To begin the leak test, the testing fixture seals the plastic tubing and then opens it to a regulated air pressure. Once the pressure stabilizes, the air input valve closes forming a sealed section of plastic tubing. Over the next few seconds, the controller monitors the pressure inside the plastic tubing to watch for a drop in air pressure. The pressure sensor in each test head is accurate to hundredths of a PSI and the output data is graphed and compared to limits for a known good part. If the pressure decreases past the acceptable limits, the tubing fails the leak test and the operator discards it as defective.

Testing for Occlusions The occlusion test measures the backpressure upon an object that is restricting flow from the compressed air supply to the atmosphere. The test measures the backpressure at the inlet of the plastic tubing. If there is an occlusion, it will cause the inlet pressure to increase and the backpressure will be higher than normal. This means there is an obstruction in the tubing and this is a defective part.

Conclusion The client wanted to work with a company that can handle high expectations with engineers that can provide superior and reliable automated tests for their products. The client chose Cyth Systems for this project because of our expertise in life science applications and our ability to cater to customer needs, especially when it comes to the quality of the design, time constraints, design limitations, and affordability.

When standard off-the-shelf testing options couldn’t provide the accuracy needed or meet the timing requirements, Cyth Systems and the Circaflex platform could provide a cost efficient solution that met all of the customer’s needs. With the Circaflex platform, we were able to perform all of the IO and calculations required to not only do the testing of the pressure in the part but also handle the physical interaction with the part as well.

Most importantly, we were able to do all of this in the 10-second test time required by the customer.

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