So what is PLATO?

is a multi-channel hardware/software system solution- is designed specifically for measuring noise/vibration (“NVH”) signatures of rotating machines such as automotive powertrain & power-steering products- provides precision order-locked analysis, using a product shaft speed reference signal to synchronise data acquisition to exact shaft speed- provides an automated data capture & processing environment in addition to in-depth interactive graphing / reporting- provides expected order and unexpected (“ghost”) order grading / comparison metrics- provides a range of add-on software modules to extend its capabilities in specific analysis and/or application areas

Why Test in the Factory?

Increasingly, passenger car occupants are becoming used to very low levels of in-vehicle noise. Vehicles are being judged by their perceived level of “NVH refinement”. Background noise levels continue to fall as contributions from wind and tyre noise are increasingly reduced, so powertrain noise, if not reduced in equal proportions, risks being heard above background. Demands for higher torques and lighter materials also compound this situation.

Most powertrain noise/vibration tends to be highly tonal in nature and even the most untrained human ears can be shown to be very sophisticated discriminators of such noises. The issue is generally not whether the passenger/driver feels they are about to be let down mechanically, but rather how comfortable they are and how that makes them feel about the “quality” of the vehicle in which they are travelling. As a result, subjectivity abounds, which makes it harder for vehicle manufacturers to disprove the complaints of disgruntled customers.

But Testing Costs Money – Doesn’t It?

Obviously, implementing a test, where previously there was no testing taking place, increases the manufacturing cost of each assembly. It is also a truism to say that implementing more testing can never increase pass rates. Therefore, factory based testing only makes sense when the test system can predict how end-customers will rate each product in-vehicle.

The “Big Picture”

A properly implemented test strategy, using a test system that generates meaningful results can be shown to dramatically reduce the overall costs to a manufacturing organisation, purely because the costs associated with testing can be far out-weighed by reductions in warranty returns.

Configurable Software

PLATO is PC-based and runs on a Microsoft Windows TM (2000 Professional or XP Professional) platform. Highly configurable software projects (using an intuitive tree structure) allow testing resources to be configured and multi-stranded NVH test procedures to be defined. Once defined, the project tree can be password protected to only allow access to those competent of making changes. Much use is made of testing templates. These allow similar products to be tested in similar ways, yet flexibility is also provided for each model (product type) definition to override default settings. Adding new product types is then a very straightforward exercise. Once a test has been completed, salient summary results are stored in state-of-the-art databases, so they can be viewed locally or via a network connection. At the same time, options exist to store “raw” (detailed) results, facilitating further in-depth (off-line) analysis.

Noise/Vibration (Dynamic) Sensors & Locations

The choice of noise/vibration sensors and where they may best be located depends on the type of product being tested, the build state of the product at the time it is tested, the specific details of each test stand and the test time available. For example, products with large airborne noise radiating surfaces may be successfully tested by measuring an array of microphones (with stand-off distances of around 0.5m to 1.0m), but only if the test environment is quiet enough to allow the product noise to stand out above the background noise. As an alternative, non-contacting laser vibrometers can be considered provided they can be suitably located on vibration-isolating mounts. For fast production testing, it is almost always impractical to attach surface vibration sensors to the product prior to testing, but it is commonplace to permanently attach accelerometers to parts of the test stand adjacent to the product e.g. on clamps and location points. By contrast, product such as axles, differential units and power take-off units tend to be very stiff structures with limited airborne noise radiation surfaces. A large proportion of these products’ “NVH energy” is therefore shaft-borne, so shaft-borne sensors such as torsional accelerometers and dynamic torque sensors make sense.

Reliable “Front-End” Hardware

PLATO currently uses front-end hardware from Cambridge Electronic Design Ltd (based in Cambridge, England). The CED POWER 1401 is a worldwide standard data interface unit. Using StrongARM technology, it can capture 8, 16, 24 or 32 dynamic input (analogue) channels with 16-bit (±5V or ±10V) accuracy up to 625KHz across channels - via a simple and fast USB2™ plug-and-play connection to just about any PC you chose to use. The on-board 32-bit RISC processor and up to 256MB of fast-access RAM free-up valuable time for the host PC to perform other activities such as graphical display. PGF8 “top-boxes” (8-channels per box) then attach to the POWER 1401 to tailor the unit for PLATO and the specific requirements of high speed, high precision and shaft speed synchronised data sampling. Pulsetrain signals from shaft encoders, magnetic sensors etc. are fed to the trigger inputs to directly control data sampling and drive shaft speed tracking analogue anti-alias filters. High-precision (calibrated) gains may also be set by PLATO software, specific to each channel, allowing ADC analogue ranges to be optimised