Machinedesign 2931 Lt Scopes 0

Not your father’s oscilloscope connectivity

March 8, 2012
Even less-expensive oscilloscopes provide data in a variety of formats once available only from top-of-the-line instruments

Authored by:
Richard Markley
Agilent Technologies Inc.
Santa Clara, Calif.
Edited by Leland Teschler
[email protected]
Key points:
• Some scopes now include a Web server that is hosted from the instrument. Instrument store/recall state capabilities can be used to speed setup of front-panel settings.
• Some instruments allow their states to be saved as files, which can then be stored to a USB drive and loaded onto another instrument.
Agilent Technologies Inc.
LXI consortium Web site

Like most technologies, oscilloscopes have evolved over time. Digital-storage oscilloscopes, or DSOs, are now the preferred type for most industrial applications. And features that once were available only on expensive, premium DSOs are now becoming commonplace on even “non-Windows” scopes that start in the $2,000 range. Upgradable bandwidth, deep memory, large displays, and fast update rates are just a few examples. In the past, only higher-end oscilloscopes have offered features such as Ethernet and USB connections. Less-expensive offerings have gone beyond floppy-drive storage and GPIB programming.

New connectivity options have started to trickle down to less-expensive oscilloscopes. In almost all cases, USB has replaced floppy drives as the de facto connection on oscilloscopes. Now to save a screen or data file, users simply insert a USB thumb drive into a connection typically referred to as a “USB Host.” Some oscilloscopes today can support USB thumb drives up to 128 Gbytes of storage. In addition to USB Host connections, many oscilloscopes now have USB Device connections. Instead of being used to connect thumb drives, these connections permit remote control of oscilloscopes via USB. To enable this connection, you connect a USB cable between a USB Host port on a PC and the USB Device port on the oscilloscope.

A USB Device connection typically involves some sort of driver library. Scopes from Agilent Technologies Inc., Santa Clara, Calif., for example, use an IO Library, which includes a connection expert program to assist with setting up the link to the scope. With the connection established, remote commands can control the oscilloscope.

Ethernet connectivity
While USB connectivity has been relatively common in scopes for some time, Ethernet connectivity, particularly on less-expensive, non-Windows scopes, is fairly new. Users can remotely control a scope over Ethernet and even hook the instrument to network-based printers. And a new type of Ethernet connectivity, called LAN eXtensions for Instruments (LXI), provides an entirely new way to interact with such test equipment.

There are many differences between LXI and the earlier GPIB standard which permitted the remote programming of instruments. LXI uses standard computer IO as the communication method. The LXI standard also defines a standard framework for Web-based interfacing and programmic control. In addition, the LXI interface supports peer-to-peer and master/slave communication and distributed systems other the LAN. And because LXI is based on Ethernet, designers can get better communication throughput as Ethernet speeds rise from 10 to 100 Mbytes/sec and 1 Gbyte/sec.

The first Agilent scope to have LXI compatibility was the 80000-Series, introduced in 2006. A few months later, LXI came to the 6000-Series of scopes as well. LXI makes it easy to configure a test system and integrate other instruments into it using a variety of connectivity options (including legacy standards like GPIB). It also has special capabilities for interacting with the oscilloscope.

For example, LXI instruments from Agilent host a Web server in the instrument itself. This integrated Web page gives users several conveniences. For example, it identifies oscilloscope information, like the model number, serial number, host name, IP address, and VISA (address) connection string. It also implements a front panel through which a user can control the scope remotely. In addition, the instrument can store and recall its settings. Some instruments allow the state to be saved as a file, which can then be put on a USB drive and loaded into another instrument. There is also an ability to send SCPI (Standard Commands for Programmable Instrumentation) via an applet window.

LXI lets a PC interact with the instrument in tasks such as saving/recalling setups and waveform data (in multiple formats). It’s also possible to capture screen images on the PC for easy addition to documents. Another convenience is the ability to have a message flashed on the instrument to identify it — helpful when you want to identify the scope as it sits in a large rack of scopes. Finally, LXI provides an opportunity to remotely install firmware upgrades.

Similarly, LXI-based instruments can be controlled via a remote front panel displayed on a PC. Today, remote front panels are strictly for PCs. The feature won’t work natively on an iPad or iPhone, although some virtual-network computing (VNC) clients can be used to see and control the remote front-panel interface of Windows-based oscilloscopes. The remote front panel recreates all the oscilloscope functions. Some oscilloscopes, like the Agilent InfiniiVision X-Series, allow use of either a simplified, basic remote front panel or a remote front panel that exactly recreates the physical oscilloscope front panel.

The basic remote front panel is useful for remote control on a PC that has limited screen resolution in that it takes up a smaller area. It is also more suited to being driven by a mouse than a finger.

A full-blown remote front panel is useful for someone who frequently operates the scope both directly and remotely — there’s no difference between the two operating modes. In addition, the remote front panel can work via a touchscreen PC rather than depending on mouse clicks.

A remote oscilloscope front panel is particularly helpful for training and education. For example, when bringing up a new production line or getting a group of engineers up to speed on instrument functions, all users within the same firewall can log in to the scope and see the actual front panel they will encounter when they receive their new scopes. They can practice on the remote panel, learn how to interact with the scope, and immediately feel comfortable when their new lab is up and running.

Similarly, remote operation is helpful for teaching institutions where access to a scope is limited. Of course, multiple operators can’t operate the scope at the same time, but a remote control is extremely useful for minimally equipped labs where sharing is the norm.

A remote front panel also comes in handy when debugging involves multiple teams spread out geographically. A team of engineers in another lab can see the scope display and settings as engineers on site demonstrate the problem.

© 2012 Penton Media, Inc.

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