A leading international medical devices manufacturer planned to automate a manual device functionality test. The upgraded system involved regulating a pressurized fluid supply and monitoring the flow rate of minute amounts of liquid from a delivery system through a small catheter and into prospective patients.


The unit, which became known as a micro intervascular catheter liquid flow/leak test system, was designed to interface with and monitor the flow of fluid (0.5 μL/sec to 10.0 μL/sec) from delivery system at a given pressure (0-3500m bar). Once this flow rate had been measured and was within the required limits, the pressure was raised and the device was monitored for leaks. The temperature of the fluid was also monitored closely throughout the process.

On receipt of the user requirement specification (URS), a functional specification (FS) was drawn up describing the higher level functionality of the system and outlining the expectations of these functions. This was presented to the medical devices supplier and on acceptance, STERIS engineers generated a design specification (DS) detailing how they intended to fully implement the functionality they committed to in the FS.

STERIS then set about the component specification for this project, a very complex process due to the high precision required. A variety of parts had to be tested and rejected before components that met the required specifications were found. For example, a large number of valves had to be rejected before one was found that did not interfere with the very sensitive monitoring of the flow rate or in any way introduce measurement errors due to fluid temperature changes. Upon completion of this phase, a bench test was carried out to test the interactivity of the separate components using a basic program developed by STERIS engineers.

Once it had been confirmed that this basic code controlled the various components, a more complex code was developed to oversee the running of the flow/leak test system and to diagnose failure modes by communicating unambiguously with the operator about what did or did not work during a particular test.

In tandem with the code, the enclosure for the unit was developed along with wiring and design diagrams for the hydraulic, pneumatic and electrical components of the system. Once the code had been finalized a number of technical documents were generated including the Calibration Instruction, Maintenance Instruction, Bill of Materials and Software Code Listing.

The finished prototype, the delivered item, in this case, was then put through a debugging process and an Operator Guide was created. There was also a full suite of environmental testing completed on the unit in an attempt to mitigate against any unforeseen problems caused by potential operating environments.

One of the challenges to be overcome was taking account of temperature changes throughout the day. Due to the sensitivity of the unit, slight environmental changes were having an effect on the flow/leak test system’s performance. These changes in performance were characterized by performing environmental simulation studies in a climatic conditioning chamber.

Following on from that, the qualification testing process began with tests and failure modes created to show that the unit had been fully tested in-house ahead of the factory acceptance test (FAT). After a successful FAT, STERIS’s micro intervascular catheter liquid flow/leak test system was delivered to the Customer.

A site acceptance test (SAT) was then carried out followed by an installation qualification (IQ) and operational qualification (OQ) and proceeded by the performance qualification (PQ). Following a successful SAT, there was an unexpected request for altered functionality. STERIS’s experts added some new error modes and re-wrote a large quantity of the software to meet these requirements. The software listing was re-checked and re-issued on-site, and validation documents were updated to reflect the recent system changes


The micro intervascular catheter liquid flow/leak test system project commissioned to STERIS posed a number of challenges for the company’s experienced design and fabrication teams.

The entire unit had to be designed and built from the ground up. Testing had to be carried out from the earliest stages of the project and continued throughout until its conclusion accompanied by reports and documentation to ensure that the Customer was always fully informed as to the progress at each stage. While the team working on the project faced a number of challenges, they overcame each obstacle.

All regulatory requirements both external and internal were satisfied. The resulting tester met with a very positive response from the Customer.

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