The Anritsu Company serves telecommunications customers who have large networks with distant monitoring substations. The company installs racks of diagnostic equipment in these substations to monitor the health of the network. When a problem arises, a trained technician diagnoses the problem with the same diagnostic equipment. Consequently, the technician must travel to the monitoring substation. To save time and money, Anritsu wanted to provide its customers with a remote control capability for its instruments in the diagnostic rack.
The primary instrument in such a rack is the Anritsu MS9720A, a WDM tester. The MS9720A integrates an optical spectrum analyzer with specialized WDM analysis functions. The instrument implements nine different measurement modes, including the spectrum analyzer and WDM tester. Each mode displays its own set of graphs, tables, and menus on the built-in CRT on the front panel. The remote control program needed to duplicate the front panel interface as closely as possible, so technicians already familiar with the instrument could use the program with minimal retraining.
Another Anritsu goal was to meet customer demand for lower cost equipment solutions. To meet this need, Anritsu has begun producing versions of the MS9720A that do not have the front panel CRT, knob, and buttons. Because the remote control program already duplicates the front panel interface, the program serves as the virtual front panel for the new instruments.
Implementation of the Process
The remote control program had to implement front panels very similar to those of the actual instrument. Because making virtual front panels is straightforward in LabVIEW, it was the natural choice for the development system. We chose to implement the application in three layers - the user interface, the instrument proxy, and the instrument driver. At the top level, the user interface implements the front panel controls and indicators and processes the user input from the controls and menus. Because the virtual front panel is running on a standard PC running Windows, we used the keyboard and mouse to simplify some aspects of the instrument front panel. For instance, the instrument uses the knob to aid in entering numbers or in selecting letters to form a title.
Another user interface improvement came from the ability to use the mouse to drag cursors on the graphs. This LabVIEW feature simplified the programming and smoothed the users’ interaction with the cursors, so users can simply click and drag the cursor rather than going through the tedious selection process used in the more limited interface on the instrument.
The user interface code calls the instrument proxy layer to control the instrument and get its settings and data. The instrument proxy isolates the user interface from the details of sequencing the commands needed to control a particular mode. Each measurement mode also keeps a nonvolatile backup of its last settings, so when the user changes modes, the new mode sets the instrument to those settings. The proxy layer is responsible for retrieving all the settings of the current mode, which happens after changing to a new measurement mode or connecting to the instrument when the program initializes.
The instrument driver layer is the familiar concept of a set of VIs whose built-in GPIB and serial communication capability sends commands and queries to the instrument. We implemented the instrument driver using VISA, which gave us an easy way to meet the key remote communication design goal.
LabVIEW and VISA gave us a powerful foundation on which to build our application. With the VISA functions, we could build the drivers and the application on top of the GPIB communication mode and switch over to serial mode late in the project with only the minimal work of changing the communication initialization function. The front panel controls and indicators, along with the power of LabVIEW attribute node programming, gave us the right set of tools to implement the virtual front panel.
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