Connecting Instruments via GPIB

Use the following video tutorials or the document below to assist you in completing this task:

Configuration in Windows for USB

Configuration in Windows for Ethernet/LXI

Configuration in Linux

Configuration in Mac OS X

The Measurement & Automation Explorer (MAX) utility comes with the NI-488 driver for your GPIB controller. MAX makes GPIB instrument detection and control easy by providing tools to help you search for connecting instruments, and communicate with your device.

Open MAX by going to Start»Programs»National Instruments»Measurement & Automation. To confirm that your GPIB device is connected properly, expand the Devices and Interfaces subdirectory below My System.

Figure 1. MAX Main Menu

Then select your GPIB controller and click on Scan for Instruments (Figure 2). This tutorial uses a USB-GPIB-HS controller. If you are using a PCI, serial, or Ethernet controller/converter, the name may be slightly different.

Figure 2. Scanning for Instruments in MAX

If your GPIB device is SCPI-compliant, the name and address appear in the lower main window once the instrument name in the configuration tree has been clicked.

Figure 3. Attributes Tab for an Instrument

If your device did not appear, refer to GPIB Installation/Configuration Troubleshooter. Also refer to KnowledgeBase 1UO68A5P: "Scan for Instruments" Fails in Measurement & Automation Explorer.

MAX creates the necessary resources for VISA communication with your GPIB instrument. By selecting the instrument from the subdirectory on the left and then selecting the VISA Properties tab, you can change the VISA Resource Name of the device and communicate with it by clicking on Communicate with Instrument (SCPI commands) or Open VISA Test Panel (non-SCPI commands).

Figure 4. VISA Properties Tab for an Instrument

Using the VISA Interactive Control to Confirm Communication and More

The VISA Interactive Control (VISAIC), is a standard software utility included with NI GPIB controller products. Using your computer, you can take advantage of this powerful development and debugging tool to interactively communicate (read, write, serial poll, and so on) with your GPIB instruments. With the VISAIC utility, you can speed up application development by learning how to automate measurements with your instruments, uncover GPIB problems, and avoid headaches by identifying malfunctioning instruments. For Windows platforms, the VISAIC utility comes with on-line help that describes the applicable NI-488 functions and NI-488.2 routines, syntax, error codes, and status variables that offer the debugging information you need to solve problems.

For a detailed discussion on how to use the VISAIC utility and the functions in the examples, refer to the VISA help file and NI-488.2 help file, respectively, that came with your GPIB controller. The following sections assume a basic knowledge of the VISAIC utility and GPIB.

To access the VISAIC in MAX go to Tools»NI-VISA»VISA Interactive Control. You can also expand the Software tab within MAX, expand the NI-VISA sub-directory, right-click NIvisaic.exe, and left-click the Launch button.

Figure 5. Launch VISAIC

Quickly Determining GPIB Addresses

When VISAIC initially runs, it automatically finds all of the available resources in the system and lists the instrument descriptors for each resource under the appropriate resource type. Figure 7 shows the VISAIC opening window.

Figure 6. Visa Interactive Control

Instruments must be powered on and connected to the GPIB controller to be recognized. If you have two or more instruments on the bus, you can disconnect all instruments except one to determine its address. By isolating each instrument on the bus and repeatedly refreshing (View»Refresh), you can quickly determine the address of each instrument. You also can use the Resource to Find field to query each instrument for an identification (ID) string. ID querying is discussed in the next section.

Establishing Communication With Your Instruments

Once you have determined the GPIB address of your instruments, it is easy to establish communications to verify that you can send and receive data to and from the instrument. Because most instruments are compliant with 488.2, you can query the instrument for its identification by sending it the *IDN? command. Instruments typically respond with the manufacturer's name, model name, and various alphanumeric characters that the manufacturer uses to track firmware revisions. To communicate with your instrument at Address 4, follow these instructions:

First, double-click the instrument in the VISAIC that you want to communicate with— in this case, GPIB0 ::4::INSTR.

This opens a VISA Test Panel for your instrument. With this test panel, you can set properties for your instrument communication as well as read and write to the instrument.

Figure 7. VISA Test Panel

From the Basic I/O tab, select the *IDN?\n command, which is the 488.2 instrument identification command "*IDN?" followed by the termination character "\n." Next, press the "Write" button to send this command to the instrument. Finally, press the "Read" button to read back the response from the instrument. Your instrument should return an identification string that appears in the window. You also can perform both a write and a read automatically by pressing the "Query" button.

Now from the viRead tab, select a count of 100, the length of our expected response, then click Execute. Our instrument should return an identification string.

You have just confirmed communication with your instrument. Repeat this process to confirm communication with all of your connected instruments.

Figure 8. VISAIC viREAD

An Easy Way to Troubleshoot Instrument, Cable, and Power Problems

Many times, systems are powered down and cables are disconnected from instruments for maintenance or system configuration changes. Unfortunately, engineers sometimes forget to reconnect all the cables and power up all the instruments. Alternatively, system power may be disrupted for a variety of reasons or the actual instrument may begin to malfunction. VISAIC is also convenient for verifying that your instruments are still "alive" on the bus. Simply use the refresh (View»Refresh) to check if a particular instrument is listening at its assigned GPIB address. If it is not, then you know to check cables, confirm power, and verify that the instrument is working properly.

If there is a problem, you no longer see your device. This indicates that you should check for loose or disconnected cables, power disruption, or a malfunctioning instrument.

The basic functions and concepts described above may seem simple; however, they can be invaluable in troubleshooting and getting your GPIB system up and running. These productivity tools help you focus on developing your test applications instead of trying to track down obscure problems or establishing communications with your instruments.

Once you have completed these steps, you need a fast way to progress from interactive mode to programming mode so you can immediately begin writing your tests without a tedious transition process. The best way to achieve this is by using instrument drivers.

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