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Test gets real

System test complexity is increasing. An obvious statement, perhaps, but the fact is that, as products become more complex and time to market pressures increase, making sure the product does what it says on the label is paramount.

There are a range of factors which come into play, such as increasing bandwidth and the range of frequencies which need to be measured. Some of these parameters can be measured adequately with an oscilloscope, but system requirements are broader. Apart from measuring specific parameters, system test may well monitor how the application performs. And the challenges increase when subsystems are involved.

John Hayward is test systems product manager with Brighton based industrial manufacturer and distributor Amplicon, which has recently established a test systems division. "The company has been making industrial computers for some time and we've found that 36% of them are being used for test. That's quite significant." Amplicon's test system division is intended to make the process of developing and procuring a test system easier. "We're not new to test. We have the communications, computing and data acquisition expertise," Hayward continued. "We can mount those elements in a rack and provide the customer with a solution that does what they want."

Hayward sees a lot of Amplicon's equipment being used for production test purposes. "Companies building set top boxes, for example, are looking at product quality and that involves measuring a wide range of parameters. They might look at rf signals, frequency bandwidth and pulses. They might be looking at voltage signals around the board and providing power to the unit. They may want to measure voltage rails," he noted.

Tristan Jones is technical marketing team leader with National Instruments UK. He pointed to the need for flexibility in test systems and suggested that multicore processors are the way to provide it. "There is a growing move to software defined test and taking advantage of multicore processing will be important. Multicore will be an advantage when testing things in parallel, particularly when it comes to testing subsystems."

National Instruments is, of course, the developer of LabVIEW and believes the package is an ideal platform for system test. Jones continued: "Test diversity is growing and we're continuing to add more productivity tools to LabVIEW to take advantage of its inherent parallelism."
Looking to support test diversity, NI has added support for real time maths in LabVIEW. Jones said: "It supports the ability to take complex algorithms and to run them on real time hardware, potentially as part of a test system."

He admitted this feature comes more from the control side of things than it does from test, drawing parallels with software in the loop. "But, as part of the test process, people are using a real time operating system to emulate the determinism of what's being built. It's all about getting your algorithm on to real time hardware and that's important."

And hardware in the loop is another important element. "Having a model in the loop when you're building a physical system helps to simulate the control aspects," he claimed.

He cited the example of an engine control unit (ecu). "It's an embedded control system with multiple subsystems. It needs to interface with other electronic systems in the car, so running the model on a hardware in the loop system allows the world around the ecu to be simulated. The I/O features allow the ecu to be function as if it was installed."

This is said by Jones to be just one example of how test is moving away from a static basis – stimulus and response – to a dynamic basis, where product functionality is tested in a real environment, but safely. "Tests need to be deterministic," Jones believed, "so the unit under test can't distinguish between the real and virtual worlds."

Amplicon's approach is to build a system to meet the customer's requirements. Hayward said: "We're a tier one distributor for a number of companies with relevant technology that can go either into an industrial pc or into a PXI system." Although Amplicon's main business is with system integrators, it also deals directly with customers building bigger systems."

Amplicon recently delivered a system to test flow computers to a company manufacturing instrumentation for the oil and gas industry.
The requirement was for an integrated test system to replace benchtop equipment and custom hardware. The new system had to reduce costs and increase productivity.

The solution has two elements: a small system, which generates 16 4 to 20mA signals and reads the status of the 12 relays on each flow computer; and a larger system, which can test up to 16 flow computers simultaneously.

The real time data acquisition system is based on two Data Acquisition Processor cards from Microstar Laboratories installed in an Amplicon Industrial PC. Other elements included 32 analogue output cards and 12 digital input cards installed in two 19in rackmount enclosures, along with rack mounted oscilloscope, monitor and keyboard.
According to Hayward, this COTS solution enabled a cost saving of £100,000 over an in house system.

NI, meanwhile, is looking to fpgas as the enabling technology for future test systems. "It's a differentiating technology," Jones noted, "and is a key part of making test systems successful because real time on its own isn't enough to meet the demands of multiple loops running at megasample rates."

NI is building platforms with a COTS approach to using fpgas. The PXI based systems can run in real time, supporting digital, rf and analogue measurements. "By adding fpgas," Jones continued, "we have far more I/O and the ability to add more timing and synchronisation flexibility, as well as the ability to put more intelligence behind that to build dynamic test systems."

One of the components of such a system is the R series. "This comprises an fpga embedded on a PXI card," said Jones. "There's no hardware integration needed and decision making is based on what you're getting back from the test."

More recently, NI has introduced FlexRIO. "This is fpga based," Jones continued, "but has an additional layer of customisation. It breaks the instrument into two parts: an fpga based back end for algorithms, intelligence and so on; and an I/O front end. It's a common architecture, but the adaptor is interchangeable and can be completely customised."
In the end, Jones believes, it's NI's experience in implementing systems with real time I/O that's important. "The next step," he concluded, "is to put real time algorithms on test systems, allowing us to move forward to hardware in the loop test."

Author
Graham Pitcher

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