Virtual reality
March 1st 2005 Low-Cost and Portable Data Acquisition: Virtual Instruments on the Factory Floor by Ian Bell, National Instruments
Machine builders, plant engineers and maintenance departments are constantly being driven to improve equipment utilisation and reduce costs.
The pressure on manufacturing businesses from overseas competition means that these improvements have to be delivered with fewer people and in less time.
Measurements are a crucial part of every company’s efforts to maximise plant efficiency, so a measurement architecture that can keep pace with the demanding requirements of modern manufacturing is essential. To address these demanding requirements, many powerful measurement technologies, with long track records in electronics manufacturing test and R&D, are now finding their way into factory applications.
The virtual instrument system is one such technology which is gaining rapid acceptance. A virtual instrument system (often shortened to virtual instrument) is a software-defined system, where software based on user requirements defines the functionality of generic measurement hardware. It is the software-defined nature of virtual instrument systems which is the most significant. Software running on the powerful processors of industry standard computing platforms allows for the use of low cost generic measurement hardware, such as multifunction data acquisition devices, by allowing users to easily reconfigure their measurement systems for a diverse range of applications. The same virtual instrument system concept can be used for machine control, machine condition monitoring, data logging and fault finding/diagnostics.
Virtual instrument systems are made possible because of three basic technologies. First, industry standard computing platforms, such as laptops, PCs and PDAs, deliver significant processing power. Second, readily available commercial technologies such as high speed/high resolution ADC devices, PCI and USB, developed mainly for consumer electronics applications, have enabled the development of small, low cost measurement devices. Finally, powerful and easy-to-use software, such as National Instruments’ LabVIEW graphical programming environment, allows users to rapidly reconfigure their measurement systems based on changing requirements.
To illustrate some of these concepts, let’s examine some factory floor scenarios where virtual instrument systems are employed.
Many custom machine architectures now include some form of embedded or industrial PC with both PCI and USB interfaces. Multifunction data acquisition (MIO) devices for PCI or USB have a wide range of I/O capabilities, including analogue voltage inputs, analogue voltage outputs, digital and counter/timer I/O. MIO devices, such as the recently introduced NI M Series and low cost USB-600x range, are now found at the heart of many custom machine systems. Virtual instrument systems using the same low cost data acquisition devices are also finding their place in machine condition monitoring and other long-term diagnostic monitoring applications. This field has traditionally been dominated by turnkey solutions, that are expensive to customise, or fixed functionality units, like chart recorders, that cannot be customised.
Building a datalogger using low cost data acquisition devices, such as the M Series and USB devices described above, allows the plant engineer to connect to a wide variety of different sensors and to adapt the system to each new application by changing the software. A common approach is to build up a “diagnostic trolley” by installing a standard PC with an M Series data acquisition card, as well as connectivity options, into a lightweight trolley which can be wheeled around the plant. A range of software is used, from a simple turnkey datalogger, such as NI VI Logger, through to custom configurations using LabVIEW. Many such trolleys are self-contained systems, using floppy disks for data transfer and having a printer as part of the trolley setup. With the introduction of wireless networking at many manufacturing plants, report printing, data transfer and even system monitoring can now be carried out remotely.
Maintenance engineers typically use a collection of handheld and portable measurement devices. When working with sophisticated manufacturing systems, engineers will often be carrying around an oscilloscope, digital multimeter and a vibration analyser. Taking the virtual instrument approach, these measurement requirements can be consolidated into a single system whose personality can be changed on-the-fly via software. A lightweight laptop, with wireless networking, connected to a compact, low cost USB data acquisition device, provides the measurement capability, while also being network connected and far more portable. If the ultimate in portability is needed, the PDA is now a viable virtual instrument platform. Microsoft PocketPC and Windows Mobile-based PDAs, as well as PalmOS-based devices are all supported by LabVIEW. PDAs have enough power for all but the most demanding applications, can be connected to PCMCIA and Compact Flash data acquisition devices and offer the greatest portability. A modern PDA-based virtual instrument system can combine multimeter, oscilloscope and datalogger capabilities, along with easy reconfiguration via software, all in a package which slips into your shirt pocket.
Ian Bell is UK & Ireland technical marketing manager with National Instruments and can be contacted at ian.bell@ni.com. More articles from National Instruments UK Limited: | 
