Install NI GPIB-USB Controllers
1. To install the GPIB-USB interface, connect the USB connector from the GPIB-USB interface to an available USB port on your computer.
2. Before connecting the GPIB-USB interface to GPIB devices, ensure that the computer and the GPIB devices are at the same ground potential. The GPIB-USB interface connects directly to most GPIB devices without requiring a GPIB cable.
3. If your computer is already running, the operating system automatically detects the GPIB interface. Otherwise, the GPIB interface is detected when you start your computer.
Figure 1. NI GPIB-USB
Caution: The GPIB-USB hardware does not have isolation built into it. If you have a system where there are different ground potentials involved, the voltage difference could surge through the GPIB hardware and cause damage. This situation most often occurs when the PC is a laptop running on a battery and the GPIB device is powered by an AC wall connection.
To prevent damage to the GPIB-USB hardware or other components in your system when different ground potentials are involved, do any of the following:
• Buy a GPIB-120A, which can provide up to 1,600 V electrical isolation between GPIB systems. You can find these at ni.com.
• Buy a pair of GPIB-140A units, which extend a GPIB system using fiber optics.
Because the GPIB signals at each end are transformed into fiber-optic signals, each unit can reside at a different ground potential. You can also find these at ni.com.
• Use a USB isolated hub. National Instruments does not sell these, but there are many available for sale elsewhere on the Web or in stores.
• Change the system setup so that all components in the system share the same earth ground to eliminate the possibilities of voltage differential running through the system.
The GPIB hardware installation is now complete.
Use the following video tutorials or the document below to assist you in completing this task:
The NI 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 you tools to search for connecting instruments, and send and receive communication with your device.
Open MAX by clicking on the icon located on your desktop or by going to Start»Programs»National Instruments»Measurement & Automation.
Figure 2. MAX Main Menu
To confirm that your GPIB device is connected properly, expand the Devices and Interfaces subdirectory below My System. Then select your GPIB controller. In this tutorial, we use an NI USB-GPIB-HS controller. If you are using a PCI, serial, or Ethernet controller/converter, the name may be slightly different. Click on Scan for Instruments.
Figure 3. 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 scan is complete.
Figure 4. GPIB Device Found
If your device did not appear, refer to GPIB Installation/Configuration Troubleshooter. Also refer to KnowledgeBase 1UO68A5P: "Scan for Instruments" Fails in Measurement and Automation Explorer.
MAX creates the necessary resources for VISA communication with your GPIB instrument. By double-clicking on the identified instrument (located in the lower main window of Figure 4), you can access the instrument VISA Properties where you have the ability to 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 5. Opening VISA Properties Tab
For this example, we have entered TDS2024 as our VISA Alias. It is important to choose an alias that you can immediately identify with the intended instrument. This is especially important for large systems involving many instruments.
Using the VISA Interactive Control to Confirm Communication and More
The VISA Interactive Control (VISAIC) is a standard software utility included with National Instruments GPIB controller products. Using your computer, you can use 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 complete with online help that describes the applicable NI-488 functions and NI-488.2 routines, syntax, error codes, and status variables that provide you with the debugging information you need to solve problems.
For a detailed discussion on how to use the VISAIC utility and the functions used in the examples, refer 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 launch VISAIC, click on Tools»NI-VISA»VISA Interactive Control (see Figure 6).
Figure 6. 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 below shows the VISAIC opening window.
Figure 7. 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 could also use the Resource to Find field to query each instrument for an identification (ID) string. ID querying is discussed in a section to follow.
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 our instrument at Address 4, we follow these instructions:
First, we double-click the instrument in the VISAIC that we would like to communicate with, in our case GPIB0 ::4::INSTR.
This opens a VISA Test Panel for our instrument. This Test Panel gives us the ability to set properties for our instrument communication as well as read and write to the instrument.
Figure 8. VISA Test Panel (viWrite)
From the viWrite tab, if we insert *IDN?\n and then click Execute, this sends the 488.2 identification command *IDN? to our instrument followed by a \n termination character.
Now from the viRead tab, we select a count of 100, the length of our expected response, and then click Execute. Our instrument should return an identification string.
We have just confirmed communication with our instrument. We can repeat this process to confirm communication with all of our connected instruments.
Figure 9. VISA Test Panel (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 to change the configuration of the system. 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 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 was a problem, you would 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 to avoid frustration in trying to track down obscure problems or establishing communications with your instruments.
Once this is done, you need a fast way of going from interactive mode to programming mode so you can directly begin writing your tests without a tedious transition process. The best way to achieve this is by using instrument drivers.