USB set to drive new data acquisition market

09/01/1999


I f Data Translation (Marlboro, Mass.) is correct in its prediction, the 'U' in USB (Universal Serial Bus) will also mean ubiquitous. Taking advantage of USB ports installed on most computers today, the company now makes adding data acquisition capabilities as easy as plugging in a mouse or a keyboard. The company's DT9800 Series USB function modules are said to perform just as well as plug-in boards without needing an external power source.

Tim Ludy, product marketing manager for Data Translation, recently talked with CE's Dave Harrold about how the Universal Serial Bus can be used in industrial environments.

DH: What's a practical, sustainable data rate for 8 to 10 devices?

TL: That depends on the type of device and the implementation requirements. For example, if the device is a mouse or a track ball, having the cursor move smoothly across the screen is not very important. If the device is doing data acquisition, then any missing data needs to be flagged as missing/questionable. Well-constructed data acquisition products would automatically request a data refresh. If the problem persists, the user would be informed of a possible A/D problem. If there's any loss of data, the error flag would set and inform the user. The A/D would then stop. Data Translation designed the DT9800 to sustain 100KHz data throughput. The product uses one USB port and collects data at 100k S/s. It doesn't compete with any other device for bus bandwidth because it's the only device on the port.

DH: How is compliance with USB achieved/maintained?

TL : The USB website (www.usb.org) explains it best. Four times a year USB hosts a 'Plugfest.' Developers bring their products together, plug them in, and if they work and don't crash other products, they're certified. Certified products are listed on the USB site. Only certified products are allowed to display the USB certification logo.

DH: To connect up to 127 USB modules likely requires a USB-powered hub. Who offers these and how do they work?

TL: USB-powered hubs are available from most major office supply houses for about $40. Some office supply houses even have an established USB section in their stores. A USB-powered hub permits the PC to be connected to the powered hub. The hub does three things: it provides electrical isolation between the PC and the USB modules; it provides additional power for each USB module, since the USB specification limits the amount of power to be powered from a PC port; and it manages the communication of the connected USB modules with the PC. When you fan out from a hub, you are sharing the port with other devices. You will eventually run out of bandwidth if you continue to add devices that run at high data rates.

DH: Users are seeking solutions as opposed to products. What sort of industrial solutions do you anticipate being suitable for USB implementations?

TL: USB solutions offer several advantages over PMCIA and PSI solutions. First, the ability to provide electrical isolation is a huge advantage in industrial environments. Electrical isolation is not part of the USB specification, but all good data acquisition developers wanting to safely and reliably work in the industrial environment will provide electrical isolation. Data Translation subjected the DT9800 to 500 volts and only experienced a one-bit 'hit' on the data. Second, Microsoft's support of USB gives it credibility. Third, USB's plug-and-play connect/disconnect capabilities make it extrememly portable to applications such as in-vehicle testing. The sensors in a vehicle can be quickly connected to a PC via a USB module to analyze information in a new way for a very specific test.





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