Building an Automated Audio Amplifier Manufacturing Test System Using NI LabVIEW and NI TestStand
"Using NI TestStand and LabVIEW, we experienced fast development times, easily created and edited sequences, had flexibility to rearrange test structures and sequences, and completed the system in just three months."
- Ahmed Issa,
Designing and building an automated manufacturing test system (MTS) for testing audio amplifier printed circuit boards (PCBs) with the aim to reduce test times and maximize throughput.
Using LabVIEW and NI TestStand software with PrismSound dScope Series III and audio test equipment to develop the MTS.
Ahmed Issa - Benetel Ltd
Patrick O’Halloran - Benetel Ltd
Test System Function and Equipment
Benetel Ltd. Ireland was founded by a team of engineers with many years of experience in automation and wireless product development at companies including Motorola, Lucent Technologies, and Kenwood. With our experienced team and extensively equipped laboratories, we can offer customers rapid and innovative, high-quality automated test solutions and wireless design.
Recently, Benetel Ltd. was chartered to design an automated MTS for testing a multipurpose audio amplifier PCB. The audio amplifier, unit under test (UUT), had several stereo and mono audio I/O ports and the customer required 15 different tests be performed on each UUT in 99 seconds. To test a UUT manually would have involved plugging cables in and out in different combinations. Furthermore, testing over a wide range of frequencies would have wasted valuable time.
For maximum testing throughput and minimum test times, the customer needed an automated test system with minimal operator interference. Thus, we designed a custom bed-of-nails fixture to house the UUT during test time. We used an industrial PC to control the MTS equipment and a DC power supply unit (PSU) to power the UUT. We controlled the PSU using a USB interface. Also, we grouped UUT test points into standard three-way XLR, stereo, mono, and USB connectors and fed them back to the audio test equipment.
We implemented a PrismSound dScope Series III to generate multitone sound signals that were fed to the fixture ports. Sound signals were probed from UUT test points and fed to and from the dScope for analysis through PrismSound dSNet-I/O-Switchers. We conducted sound signal analysis by performing fast Fourier transform (FFT) on the measured sound signal traces, and the assessment factors were signal amplitude, noise, and distortion. Resistor loads were applied on the UUT output signals to simulate speaker loads.
We interconnected the PrismSound equipment using an RS232 daisy chain, and controlled the devices using a USB interface. The UUT had an onboard digital sound card I/O. The digital sound signals to and from the sound card were connected directly to the PC using a USB interface and analysed using PrismSound software. We stacked the MTS equipment in a 19 in. rackmount.
We used NI software to automate the entire Audio Amplifier MTS. ActiveX controls, provided by PrismSound, were used in LabVIEW VI shells to automate the required functionality of the audio test equipment. VIs were also used to control the PSU using USB serial communication. We arranged and sequenced all VIs using NI TestStand with proper inputs, preconditions, and postactions to put together a sequence of tests that conformed to the UUT manufacturer specifications.
The UUT tests performed were comprised of DC supply voltage levels, sound card I/O, amplifier output level, bass and treble combination outputs, and auxiliary and PC stereo I/O. Reports of the test results were generated in HTML and CSV formats and we added database logging to the system for test yield studies.
Many automation and test code changes were required throughout MTS development stages. Using NI TestStand to sequence LabVIEW VIs was the optimum solution because the software allowed fast development times, ease in creating and editing sequences, and the flexibility to rearrange test structures and sequences. The simplicity of integrating LabVIEW VIs into the sequences was also a major factor.
Moreover, LabVIEW VIs made it very easy to control the PrismSound equipment using ActiveX controls. This facilitated a fast protocol for controlling the PrismSound equipment and resulted in the reduction of the test time from the targeted 99 seconds to 70 seconds per UUT. This project took three months to complete, from the proposal stage to deployment.
Test System Performance
The automated audio amplifier MTS performed reliably, offering the main speed and repeatability benefits. The modular nature of NI TestStand and LabVIEW programming added great flexibility and ease of accommodating UUT updates with little to no code changes. By using NI TestStand and LabVIEW, no extra development time was devoted to creating standard objects such as graph displays or user interface buttons. With slight modifications on the default NI TestStand interface, running the MTS required minimum operator skill due the user-friendly test executive interface.
With improved testing efficiency, the UUT manufacturer was able to decrease test time by 29 seconds per UUT. Reports generated automatically with each test provided a good reference of the results and future analysis. With database logging and yield studies, the customer was able to make better decisions about UUT failures and thereby increase product reliability, quality, and profitability.
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