Using Measurement & Automation Explorer 2.x to Configure Your IVI System

Publish Date: May 05, 2012 | 10 Ratings | 2.10 out of 5 |  PDF

Overview

Note: This document explains how to configure IVI systems in MAX 2.x. The IVI configuration utility in MAX 3.0 has been significantly changed. The updated utility is designed to work with the IVI Configuration Server to provide easy access to the configuration data for your drivers. For instructions on how to use this updated utility, please refer to the IVI help built into MAX 3.0.
    National Instruments provides Measurement and Automation Explorer (MAX), a Graphical User Interface for configuring IVI. MAX is usually installed with one of NI's Application Development Environments such as LabVIEW or Measurement Studio, or with one of our hardware product drivers such as NI-488.2 or NI-DAQ. The purpose of this Developer Zone document is to show how to configure IVI systems in MAX. It is intended for IVI class driver users who want to take advantage of all the benefits of IVI by using MAX. One of the most important features of IVI drivers is interchangeability. The IVI configuration utility allows you to interchange instruments without recompiling or relinking your application source code by configuring logical names, virtual instruments, and instrument drivers in MAX. The user defines which specific instrument he wants to associate with a logical name and IVI takes care of the rest. If at a later time, the user decides to swap the instrument and use a different one, all he has to do is change the entry in the configuration utility so the logical name points to a different specific instrument driver.

    IVI drivers also increase performance and productivity and decrease development time with the following features:

    • State caching increases efficiency by maintaining the value of each instrument attribute setting and only communicating with the instrument when that value changes.
    • When specifying attribute settings, you can enable range checking to verify and coerce settings to acceptable, predetermined values.
    • IVI drivers provide a simulation mode that allows you to make calls to an instrument driver without the instrument being present. Simulation mode makes it possible to test software with data that would be acquired from the instrument.
    • IVI drivers also have features such as status checking and record coercion.

    These features can be enabled and disabled using the option string of the Initialize With Options VI in LabVIEW or the InitWithOptions function in LabWindows/CVI. However, the options you select will be hardcoded in the source and inconvenient to change in the future or when moving from development to production mode. Using MAX gives you the opportunity to take advantage of IVI's interchangeability and the ability to enable and disable the various options in IVI from outside of the application. For more information concerning IVI, visit our web site http://www.ni.com/ivi/ or refer to Application Note 140, Using IVI Drivers in LabVIEW.

    Table of Contents

    1. IVI Configuration Hierarchy
    2. Creating Logical Names
    3. Creating Virtual Instruments
    4. Creating Instrument Drivers
    5. Creating Specific Devices
    6. Modifying Virtual Instrument Properties
    7. Conclusion

    1. IVI Configuration Hierarchy

    Figure 1. Measurement & Automation Explorer--IVI Configuration Hierarchy


    The IVI component of MAX reveals a hierarchy that enables you to take full advantage of the features IVI offers. At the highest level, the logical name is a generic entry that points to a virtual instrument. The virtual instrument contains information on a particular instrument driver and device when it is not simulating. The virtual instrument also contains settings for inherent attributes such as state caching, range checking, and simulating. You can also set virtual channel names and the default setup.

    Setting up an instrument driver requires class information. The five instrument classes (DC Power Supply, Multimeter, Function Generator, Oscilloscope, Switch) are loaded with default settings when class drivers are installed. Class drivers represent classes of instruments. Class drivers are similar to logical names, but instead of virtual instruments, they point to simulated virtual instruments. A simulated virtual instrument consists of a simulation driver (only needed when simulating through a class driver) and default setup.

    Instead of using the Initialize With Options VI (LabVIEW) or InitWithOptions function (LabWindows/CVI), you can use MAX to configure a virtual instrument and store its settings. You can initialize an instrument with the Initialize VI (or Init function) by entering the GPIB address (GPIB::2::INSTR) in the resource name as you would with a traditional driver. However, this approach does not implement the MAX settings. To implement the MAX settings enter the name of the configured virtual instrument or logical name. Using logical names and virtual instruments creates interchangeability of instruments and allows for the setting of inherent attributes outside of the application code.


    Figure 2. Example of Non-Configurable Use of Instrument Descriptor in LabVIEW



    If you want to interchange instruments in the future, use a logical name. To swap instruments, change the virtual instrument the logical name is pointing to in MAX. If you modify the virtual instrument settings in MAX, your setting changes are implemented without recompiling the application code. Consider the following example. If you previously configured the niDMM virtual instrument for a National Instruments DMM, you can set and use the Initialize VI of the specific driver. Replace the resource name string with niDMM. Figure 3 illustrates this configuration. The specific driver then uses the configuration parameters associated with the niDMM virtual instrument when it executes your application.

     

    Figure 3. Example of Configurable Instrument Descriptor by Using Virtual Instruments in LabVIEW


    The settings you make through MAX could conflict with the settings you make with the Initialize With Options VI. Therefore, if you attempt to use both approaches, you will generate errors. Make sure the option string is empty when you use the MAX approach.


    Figure 4. niDMM Instrument Driver in the MAX IVI Instrument Drivers View


    The logical names are in the IVI Instrument View of MAX. Along with Logical Names, you also see subfolders for Devices, Instrument Drivers, and Virtual Instruments. You can use logical names at both the class and specific driver level. Logical names point to virtual instruments and, when using class drivers, allow for interchangeability. Virtual instruments consist of an instrument driver, property settings and, when you do not want to simulate, a device. Instrument drivers specify the instrument driver DLL. The device properties specify the resource name to access a physical device.

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    2. Creating Logical Names

    Complete the following steps to use the wizard in MAX to create a logical name.

    1. Right-click the Logical Names subdirectory and select Insert to launch the wizard. The wizard guides you through the steps that are necessary to set up the logical name. You generally use logical names at the class driver level for matters of interchangeability although you might also use them when initializing a specific driver.

    2. Enter the logical name and a brief description. The logical name can be anything. You use the logical name in the Initialize function to access the settings in MAX.


    Figure 5. New Logical Name Dialog Box


    3. Click on Next.

    4. In the New Logical Name Virtual Instrument dialog box, choose an existing virtual instrument or create a new virtual instrument.


    Figure 6. New Logical Name Virtual Instrument Dialog Box


    5. Click on Next.

    6. In the New Logical Name Summary dialog box, the wizard shows a summary of the logical name to be created.

    7. Click on Finish when you are done creating the logical name.

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    3. Creating Virtual Instruments

    Complete the following steps to use the wizard in MAX to create a virtual instrument.

    1. Right-click the Virtual Instrument subdirectory and select Insert to launch the wizard. The wizard guides you through the steps to set up the virtual instrument. Use virtual instruments primarily at the specific driver level. You can use virtual instruments at the class driver level but doing so removes the potential for interchangeability.

     


    Figure 7. New Virtual Instrument Dialog Box


    2. Enter the name and a brief description of the virtual instrument. Use the virtual instrument name in the Initialize function to access the settings in MAX or it will be used by a logical name.

    3. Click on Next to display the New Virtual Instrument Driver dialog box.

    4. In the New Virtual Instrument Driver dialog box, choose Use an Existing Specific Driver or Create a New Specific Driver.


    Figure 8. New Virtual Instrument Driver Dialog Box


    5. In the New Virtual Instrument Device dialog box, choose Use an Existing Device, Create a New Device, or None-Simulate the Device. If you choose None-Simulate the Device, the wizard sets the virtual instrument to simulation mode.

    6. Click on Next to display the New Virtual Instrument Device dialog box.


    Figure 9. New Virtual Instrument Device Dialog Box


    7. In the fourth dialog box, the wizard shows a summary of the virtual instrument to be created. Click Finish when you are done creating the virtual instrument.

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    4. Creating Instrument Drivers

    Complete the following steps to use the wizard in MAX to create an instrument driver.

    1. Right-click the Instrument Driver subdirectory and select Insert to launch the wizard. The wizard guides you through the steps that are necessary to set up the instrument driver.

    2. To create an instrument driver, enter the driver name, a brief description, the driver file (a .dll file that will reside in the \VXIPNP\WIN95\bin\directory), the function prefix of the instrument driver, and the associated class of the instrument driver in the New Driver dialog box, as shown in Figure 10.


    Figure 10. Creating an Instrument Driver


    3. Click on Finish to create the virtual instrument.

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    5. Creating Specific Devices

    Complete the following steps to use the wizard in MAX to create a specific device.

    1. Right-click the Devices subdirectory and select Insert to launch the wizard. The wizard guides you through the steps that are necessary to set up the specific device.

    2. To create a specific device, enter the Device Name, Description, and Resource Descriptor. The Resource Descriptor consists of the interface type (GPIB, DAQ, and so on), followed by two colons, the number of the address, two colons, and finally INSTR. An example of a Resource Descriptor is GPIB::4::INSTR. The wizard is shown in Figure 11.


    Figure 11. Creating a Device


    3. Click on Finish to create the specific device.
     

    Creating Class Drivers, Simulation Instruments, and Simulation Virtual Instruments When creating instrument drivers, the wizard requires you to specify the class of the instrument. When you load NI class drivers, these entries are entered into MAX for later use. However, you can create your own class drivers, simulation instruments, and simulation virtual instruments by right-clicking on the particular directory and selecting Insert. Follow the MAX wizard to complete the configuration.

     

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    6. Modifying Virtual Instrument Properties


    Complete the following steps to modify the properties of a virtual instrument.

    1. Right-click the VI and select Properties. As shown in Figure 12, the Properties window has four tabs: Virtual Instrument, Inherent Attributes, Channels, and Default Setup. Select the tab with the properties that you need to modify.

    2. On the Virtual Instrument tab, you can modify the description and the properties of the specific driver and device. You can also change the specific driver or device used by this virtual instrument. To modify the properties of the specific driver, click Properties in the Specific Driver area which brings up the specific driver you want to modify.

    3. To change the specific driver that the virtual instrument is using, click Change in the Specific Driver area.

    4. To modify the device used by the virtual instrument, click Properties in the Device area.

    5. To change to a different device, click Change in the Device area.

    6. Click OK to save any modifications, or Cancel to undo any changes.


    Figure 12. Instrument Driver and Device Properties of Virtual Instrument


    7. On the Inherent Attributes tab, you can enable and disable the State Caching, Range Checking, Query Instrument Status, Record Coercion, Interchange Check, and Spy options. You can also enable, disable, and setup the Simulation mode. You can choose to simulate through the class driver or through the specific driver. If you choose to simulate through the class driver, then it chooses the same virtual instrument the class driver uses.

    8. You can change the simulation virtual instrument's properties by clicking Properties or clicking Change to choose a new simulation virtual instrument. To learn more about inherent attributes see the DevZone document,Using Drivers in LabVIEW.

    Caution: If you enable Record Value Coercion and never use Get Next Coercion Record VI to retrieve and clear those coercion records, the records build up and could eventually overflow your computer memory.

    9. If you want to use the virtual instrument, but have modified it to not use a device, set the virtual instrument to Simulation mode under the Inherent Attributes tab.

     

    Figure 13. Inherent Attributes of Virtual Instruments


    10. On the Channel tab, you can setup virtual channel names to be associated with the instrument's specific channel strings. In your application code, use the virtual channel name for matters of interchangeability.

     

    Figure 14. Virtual Channel Name Setup

    11. The Default Setup tab contains the configuration of the default values of an instrument's attributes. This does not usually need to be used, but in a few instances is needed to achieve interchangeability when physically swapping instruments.


    Figure 15. Virtual Instrument Default Setup

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    7. Conclusion

    IVI opens many possibilities for instrument driver users. Logical names and virtual instruments make IVI drivers interchangeable and intelligent. MAX helps you to easily and conveniently configure logical names and virtual instruments while maximizing the capabilities of IVI drivers.

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