Test system - a sound investment?

National Instruments Aust Pty Ltd
By Paul Carter, Cochlear Ltd
Sunday, 05 June, 2005

Cochlear faced the challenge of reducing escalating costs and development time for a new generation of hearing implants by creating an automated, mixed-signal test system using off-the-shelf technology.

Using National Instruments LabVIEW, PXI computer-based instruments and NI TestStand to create a suite of automated test systems, the company was able to gain greater flexibility and functionality with 30% less development time.

Cochlear, in Sydney, is world-renowned for its implantable hearing devices. The flagship product is the Nucleus cochlear implant system that consists of an internal implant and an external speech processor.

The processor analyses and digitises sounds into coded signals which are transmitted to the implant by an RF signal.

The implant converts the signals into electrical pulses which are then used to directly stimulate the cochlear never fibres to produce a hearing sensation. Each speech processor is individually programmed to meet individual hearing needs, which helps most recipients lead a normal life.

The company pays close attention to product quality and safety and test systems play a key role in ensuring quality and safety.

The implant systems are complex and involve many different parts and subsystems. Developing test systems for all these components can amount to a huge amount of time and resources - time the company does not have.

As products evolve, they become more complex and contain more components, increasing the pressure for a system that can perform. Traditionally, all the test solutions have been developed in house using custom-built hardware and software. This worked for the simpler products, but Cochlear found increasing difficulty getting test systems ready in time for product launches.

The company realises that for its latest product under development, the task has become too large to even contemplate using traditional testing methods.

With thousands of system sales annually, the company operates in a market that is rapidly evolving from a niche application into accepted mainstream medical technology. It had outgrown a DIY test approach but was not prepared to invest in a multi-million dollar test system.

The National In-struments PXI solution has proved to be the best solution for a flexible test system at an affordable price.

Cochlear uses the latest PXI-based functional test systems for in-house development testing across eight different applications from open boards to fully assembled units. It also uses the system to do production tests internally and with various contract manufacturers.

The system is required to perform a variety of actions including capture, storage and analysis of the wave shape of a 5 MHz signal, which is used to transfer power and data across the skin to the implant.

The company uses audio measurements, parametric measurement of voltages, and currents under various load conditions, digital I/O, serial, and GPIB to talk with external devices. It uses USB communications to control relays, switches and other hardware on the custom board and the system also needs to accurately tune a resonant circuit and test I2C communications.

The system generates test reports on paper but the data is also stored on the network for later statistical analysis.

A National Instruments Alliance Partner, CPE Systems, provided assistance with developing custom interface cards and software development expertise in LabVIEW and NI TestStand.

The test system comprises a PXI-based Pentium 4 controller with GPIB interface, PXI-4070 FlexDMM card, PXI-6052E multi-function data acquisition card, and a PXI-5122 high-speed digitiser.

The DAQ, FlexDMM cards and high-speed digitisers provide all the analog and digital input and outputs required for measuring mixed signal parameters and signal switching.

A conditioning amplifier is controlled by RS232 communications and USB controls another custom interface card. Smaller than any previous test systems, the system saves space on the production floor. The PXI platform means the system is flexible, easy to service and easily updateable in the future.

Using NI LabVIEW and NI TestStand, the company developed a flexible software architecture to address current and future test requirements. The software is versatile enough to test different versions of products and open and closed versions of hardware.

TestStand saved development time with off-the-shelf test executive functionality.

Using a custom operator interface, an operator logs in, loads a selected test sequence, and monitors the testing as it progresses. The interface also provides real-time information updates to the operator, generates a test report and logs all test information to a database for future analysis.

Individual tests were written in LabVIEW, which also reduced development time because of the extensive libraries available for taking measurements, interfacing to hardware, analysing results and presenting data.

By modularising and separating the operator interface sequence control from the individual test modules, the company can use the development effort across multiple products with similar test requirements.

Having all the data logged to disk in a standardised format, R&D and production engineers can mine the data for trends and generate reports on production yields.

Cochlear also uses the data to analyse failures and identify areas for improvement in the device manufacturing.

The logging records contain all test information including the sequences used, parameters, calibration dates of instruments used for the tests, test time, and pass/fail status of the units.

The test system helped the company meet schedules to push new product designs from conception to manufacturing.

TestStand, it says, has been invaluable in creating a modular, reusable test framework for LabVIEW test modules.

From a project perspective, the company can develop test systems in record time because much of the risk associated with hardware and software development has been taken out of the project.

Cochlear says initial investment in training was recouped by reducing the development time for this project alone.

In future projects, it expects to see around 30% less development time now that its engineers are comfortable using the tools.

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