Accelerating medical device testing with Averna’s NI PXI-based architecture

Author : Yvon Lemyre, Test Engineer at Averna (a National Instruments Platinum Alliance Partner)

02 November 2018

Figure 1. The AriaTele transmits real-time ECG and SpO2 data for patient monitoring
Figure 1. The AriaTele transmits real-time ECG and SpO2 data for patient monitoring

Challenged with improving production efficiency, medtech manufacturer Spacelabs Healthcare looked to accelerate its test throughput and minimise operator tasks. As this piece discusses, Spacelabs later determined that increased automation, enabled by a flexible, modular industry-standard PXI T&M platform, could deliver the long-term benefits it was seeking...

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In particular, Spacelabs turned to an integration partner to achieve its goal of accelerating electromechanical performance testing for its medical devices. To specify, Spacelabs Healthcare of Snoqualmie, Washington, USA, is a vendor of innovative medical devices, including telemetry, patient monitoring, and anesthesia delivery and ventilator systems.

The company partnered with Averna to develop ten different standalone test stations to verify the functionality of its telemetry transmission and reception modules, as well as an anesthesia delivery and ventilator system – from printed circuit board (PCB) to final assembly testing.

Averna has considerable expertise in producing integrated solutions to verify and test electronic and communication products or systems in multiple industries, including aerospace and defence, automotive, consumer electronics, life sciences, telecom infrastructure and transportation.

In addition to delivering an extensive portfolio of test engineering services and turnkey test systems, Averna offers a line of RF test instruments – such as RF record and playback solutions – for both consumer-grade products and highly specialised applications, as well as a line of broadband test solutions for Data Over Cable Service Interface Specification (DOCSIS) design and manufacturing verification, protocol analysis and channel emulation.

A multiple test station project

This case study focuses on the test solution for just one of Spacelabs’ products: the AriaTele telemetry transmitter, and details how Averna designed and implemented a test system to achieve the goals set by Spacelabs.

Many of the design principles and components described in this article, however, apply to all ten of the stations. The AriaTele, shown in Figure 1 (see image above or click here – links to online magazine version), wirelessly transmits a patient’s electrocardiogram (ECG) and oxygen saturation (SpO2) data to a remote monitoring station.

A flexible test system design

With the wide range of products to be tested, Averna and Spacelabs decided early in the project to architect the multiple test stations based on standard 19? racks and, wherever possible, modular RF test instruments (such as NI PXI and PXI Express).

For test sequencing, Averna used the manufacturing industry standard NI TestStand software and NI LabVIEW software. In addition, it implemented application-specific instruments to recreate the Spacelabs product environment. For example, the test station for the AriaTele telemetry transmitter, shown in Figure 2, comprises an ECG simulator, an SpO2 simulator and a Spacelabs telemetry receiver/captive device to produce the necessary real-world RF and medical data environment for testing each unit under test (UUT).

Standardised PXI-based architecture

The test station features many NI PXI products that are integral to its high-throughput, high-performance makeup.

Credit: Shutterstock
Credit: Shutterstock

The system uses the NI PXIe-1085 18-slot 3U chassis and also includes:

• PXI-4072 digital multimeter and LCR meter

• PXI-5124 200 MS/s, 12-bit digitiser/oscilloscope

• PXI-5421 100 MS/s, 16-bit arbitrary waveform generator

• NI PXIe-6556 200 MHz digital waveform generator/analyser with PPMU

An intelligent fixture holds the UUTs

To keep operator intervention to a minimum, the test station’s fixture features a custom sliding base plate that ensures easy unit loading/unloading, uniform UUT positioning and repeatable RF measurements.

The fixture’s integrated RF capabilities, such as Bluetooth, antenna coupler and a breakout circuit PCB assembly, enable the testing of wired and wireless interfaces – from 100 MHz to 5 GHz – to ensure reliable measurements. To protect the integrity of RF propagation during the test phase, the fixture has a Plexiglas cover that closes over the UUT during testing, as shown in Figure 3.

Automated test sequencing and execution

Perhaps the greatest advances for the Spacelabs test approach were achieved through the sophisticated test architecture, which was designed and implemented to verify all electrical and mechanical properties of each UUT.

Averna used a combination of TestStand and LabVIEW software to sequence more than 125 tests, which run automatically.

To ensure that the testing runs smoothly, even when it encounters Bluetooth communication or runtime issues, the system includes automated error handling and retry capabilities.

The test phase starts when the operator scans the barcode and places the UUT in the fixture. The system automatically recognises the unit based on information in the test platform’s Proligent database, before beginning the predetermined TestStand test sequence. The testing takes 20 to 25 minutes per UUT and comprises seven stages:

1. Boot-up self-tests – First, a power-on self-test takes place, followed by the verification of basic UUT functionality, like voltage parameters and currents for all the device’s functional blocks. The system then verifies the self-tests and configuration states (including the hardware and firmware versions on the device), and ultimately sets up the UUT’s sales order configuration.

Credit: Shutterstock
Credit: Shutterstock

2. Electrocardiography (ECG) electrode tests – Next, the system begins to test the medical functionality against the product specifications. In this case, it uses the Spacelabs ECG simulator to verify the ECG electrode status and voltage of each electrode, to determine the quality and magnitude of any stimuli or waveform transmitted through the UUT’s ECG connector port. On the ECG electrode connector port, the system simulates human impedance to verify electrode presence and effectiveness.

3. RF Tests – At this stage, the system makes frequency adjustments, before performing RF power tests; this is followed by adjacent channel power using modulated signals, and spurious RF emissions, such as in-band, out-of-band, and second and third harmonics.

4. RF data integrity tests – For this step, the system launches the Spacelabs ECG simulator to generate an ECG vector, which the UUT captures, modulates and transmits to the telemetry captive receiver. This module demodulates the ECG vector and compares it to the original ECG vector, evaluating any deviation from the expected results.

5. SpO2  tests – For models with the SpO2 option, the system next engages the SpO2  simulator to generate measurements for the saturation of peripheral oxygen and heart rate

6. Button tests – Once all of the above tests are successful, the system prompts the operator to test each of the unit’s buttons to verify appropriate behaviour and to ensure that each input delivers the expected system reaction.

7. Final tests – In the last round of tests, the system programs the unit’s sales order configuration, such as channel, frequency, bandwidth and lead type.

A paperless test environment

One of the main goals of the project was to restrict operator interactions with the test station and test routines to eliminate the impact of the operator on test results. Averna achieved this using automated sequencing and a paperless test environment. The few test steps that require operator interactions, such as the manual testing of the device’s buttons, are dictated by screen prompts.

Due to the rigid, automated test sequencing, every unit is strictly subjected to the same tests in the same order, meaning that no shop-floor improvisation is permitted. In fact, operators never touch the test station, its instruments or cabling, and cannot modify test settings or skip steps – preventing test result variability and reducing the possibility of human error.

Centralised test data collection and management

Averna’s test architecture design features automation of outbound test station data. More specifically, test results are managed by Averna’s Proligent Analytics: an automated module that gathers, aggregates and stores all test results in a central database, where they can be accessed by more than 50 reports and charts. In addition, Proligent Analytics provides a multidimensional view of the data, letting Spacelabs test engineers quickly drill down to examine any unit or batch-based test results, product component or supply chain-related issues.

Results: streamlined production testing and easy upgrades

The new Spacelabs test stations are highly streamlined and require few operator inputs, which has improved testing efficiency and throughput for the company’s telemetry products. Since the test systems are based on a design that includes a flexible test executive (TestStand) – alongside PXI modules, swappable fixtures, standard racks (with 20% extra space), and centralised test data management – Spacelabs can easily update its systems over the coming years, to accommodate new and evolving product features, ultimately protecting its test infrastructure investment.

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