USB Moves into Industrial Applications
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Technologies that are popular in PCs usually end up making their way to the industrial market.
A decade ago, the introduction of Ethernet on the factory floor was met with considerable skepticism. Engineers raised questions about its communication reliability, connector performance, and hardware sustainability under harsh industrial environments. Ethernet evolved to overcome these concerns, and engineers are now successfully using it in a variety of industrial applications from mining to offshore drilling. Ethernet has seen major success because it is readily available on commercial devices such as industrial PCs and because it has an existing knowledgebase. Now, with the explosive growth and adoption of USB in the PC industry, engineers are evaluating the viability of USB in industrial environments. USB has been widely adopted as the standard bus for PC peripherals because it offers ease of use; high data throughput; and, with an estimated 2 billion ports around the world (usb.org), it is one of the fastest-growing bus technologies in the computer industry. Because of its broad adoption and high performance, USB, like Ethernet, is finding its place on the industrial measurement scenery.
The Need for USB in Industry
The typical factory floor is a mix of sensors, actuators, relays, motors, wires, and controllers working together as an interdependent system. Running an efficient plant involves promptly troubleshooting malfunctions and constantly evaluating plant efficiency by monitoring machine vibrations, capturing digital events, and trending temperature and pressure data. Along with 24 V digital signal levels, 4 to 20 mA analog signal levels, and galvanic isolation for safety, industrial applications require a measurement system with high-speed, accurate analog input; fast data logging; and analysis capabilities. They also need a permanently installed efficiency monitoring system and a portable diagnostic system for troubleshooting.
Programmable logic controllers (PLCs) traditionally used for plant control do not offer the high-speed I/O required for diagnosis and monitoring tasks. Instead, a USB-based measurement system with industrial I/O levels and high data throughput can make demanding measurements, including dynamic machine condition monitoring. You can use USB for short-term diagnostic systems that require quick and easy setup. You also can permanently install USB data acquisition systems where industrial PCs or human machine interfaces (HMIs) with USB ports are available.
Since its release in 1996, USB has become the standard bus for connecting to computer peripherals, and today, it is readily available on industrial PCs, single-board computers, and touch panel HMIs. USB also offers a unique mix of ease of use, high performance, and reliability and security.
Figure 1. Hi-Speed USB offers up to 480 Mb/s transfer rates, connectivity for up to 127 devices on a single port, and enterprise connectivity with OLE for process control (OPC).
Ease of Use
One of the major benefits of USB is its plug-and-play ease of use, which promotes fast setup times. Major OSs including Windows, Mac, and Linux® offer built-in USB support, and most industrial PCs, laptops, and industrial HMIs contain USB ports. After you install USB device driver software, connecting a USB device to a host computer requires no action or configuration other than physically plugging the connector into the USB port. Because USB is hot-pluggable, you do not have to turn off the computer to add or remove a device, and USB bus power often eliminates the need for external power. These features greatly simplify setup and mobility, making USB a good solution for portable and short-term industrial monitoring applications.
High Performance
Machine diagnosis and monitoring can require measurements from a large number of I/O channels at high acquisition rates, sometimes distributed across the industrial facilities. Hi-Speed USB ports offer connectivity for up to 127 devices with transfer rates of up to 480 Mb/s. The USB standard defines a maximum of 5 m between the host computer and the USB device. However, with commercially available USB hubs and extenders, you can extend USB up to 30 m or 500 m, respectively.
Table 1. Hi-Speed USB is readily available on industrial computers and offers easy setup, plug-and-play connectivity, high data throughput, and reliable communication.
Reliability and Security
Reliable communication in harsh industrial environments is an absolute requirement for industrial applications. USB data transmission occurs over a twisted pair of data lines with differential signaling. This design reduces most noise that could otherwise cause data errors during transfer. In addition, to eliminate miscommunication, error checking is built into the transfer protocol. You also can use strain relief with USB cables for increased protection, and, for mechanical reliability, some vendors offer industrial-rated USB connectors with latches.
Figure 2. NI CompactDAQ offers a Hi-Speed USB interface and a range of I/O modules with built-in galvanic isolation for direct connectivity to a range of industrial sensors.
USB for Industrial Measurements
High data throughput; ease of use; reliable communication; and availability on industrial PCs, laptops, and industrial HMIs has made USB an attractive bus technology for industrial use. Many new USB-based data acquisition systems are being introduced that offer the right I/O mixes for industrial applications. For example, National Instruments recently released the NI CompactDAQ platform and new bus-powered M Series devices for USB. These devices feature built-in galvanic isolation to protect plant assets, the data acquisition system, host PC, and user from hazardous voltages. They also offer panel and DIN-rail-mounting options. NI CompactDAQ modules feature built-in connectivity and signal conditioning for the most common analog, digital, and sensor measurements, including temperature, pressure, flow, and vibration.
Together, the plug-and-play ease of use and high performance of USB make it effective for both portable and fixed-installation applications. With a growing number of USB-based industrial measurement systems offering direct connectivity to industrial sensors, USB is making an impact.
USB Data Acquisition Product Engineer
Industrial Data Acquisition Product Engineer
Take an interactive virtual tour of the NI CompactDAQ USB data acquisition system.
This article first appeared in the Q4 2006 issue of Instrumentation Newsletter as "USB Finds Its Place on the Factory Floor".
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