National Instruments’ LabVIEW and TestStand have been used in the design and building of an automated manufacturing test system (MTS) for specialists in automated test solutions and wireless design, Benetel Ireland. The MTS is used for testing audio amplifier print circuit boards (PCB) with the aim of reducing test times and maximising throughput.
The audio amplifier, or the unit Under Test (UUT) had several stereo and mono audio input and output ports. The customer required 15 different tests to be performed on each UUT during 99 seconds. Testing a UUT manually would involve plugging cables in and out in difference combinations. Furthermore, testing over a wide range of frequencies would waste valuable time.
For maximum testing throughput and minimum test times, an automated test system with minimal operator interference was sought. To this end, Benetel designed a custom bed-of-nails fixture to house the UUT during test time.
An industrial PC was used to control the MTS equipment. A DC power supply unit (PSU) was used to power up the UUT. The PSU was controlled using a USB interface. UUT test points were grouped into standard three-way XLR, stereo, mono and USB connectors and fed back to the audio test equipment. PrismSound’s dScope Series III, a measurement system for analogue and digital audio generation, was used to generate multi-tone sound signals that were fed to the fixture ports. Sound signals were probed from UUT test points and fed to/from the dScope for analysis through PrismSound dSNet-I/O-Switchers. Sound signal analysis was done by performing FFT on the measured sound signal traces and the assessment factors were signal Amplitude, Noise and Distortion. Resistor loads were applied on the UUT’s output signals to simulate speaker loads.
The PrismSound equipment was interconnected using a RS232 daisy-chain, and controlled by a USB interface. The UUT had an onboard digital sound card I/O. The digital sound signals to/from the sound card were connected directly to the PC using a  USB interface and analysed using PrismSound software.
Software Development
NI software was used 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. All VIs were arranged and sequenced using test management software, TestStand, with proper inputs, preconditions and post-actions to put together a sequence of tests that conformed to the UUTs’ manufacturer specifications.
The tests performed on the UUT comprised DC supply voltage levels, sound card input/output, amplifier output level, bass and treble combination outputs, auxiliary and PC stereo input/output.
Many automation and test code changes were required throughout MTS development stages. The use of TestStand to sequence LabVIEW VIs was the optimum solution. Using TestStand and LabVIEW allowed fast development times, ease in creating and editing sequences, and flexibility to re-arrange test structure and sequences. The simplicity of integrating LabVIEW VIs into the sequences was also a major factor. Above all, LabVIEW VIs made it very easy to control the PrismSound equipment using ActiveX controls. The latter advantage 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 benefits of speed and repeatability. The modular nature of TestStand and LabVIEW programming added great flexibility and ease of accommodating UUT updates with no or little code changes. By using 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 TestStand interface, running the MTS required minimum operator skill due the user-friendly TestExecutive interface.
With improved testing efficiency, the UUTs’ 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, they were able to make better decisions about UUT failures, and thereby increase product reliability, quality and profitability.
