The Advantages of NI Switches
National Instruments offers more than 50 switch modules and more than 150 topologies for the modular PXI and SCXI platforms. You can combine these modules with NI instruments (RF analyzers/generators, digital multimeters, arbitrary waveform generators, and so on) to build flexible, high-channel-count automated test applications.
NI switches work well for a wide variety of applications ranging from fault insertion at 40 A to surveillance at 26.5 GHz.
»See a complete list of NI switch modules.
Figure 1. NI offers a wide range of switch modules in PXI and SCXI form factors.
NI switches feature several unique advantages that can help you simplify your test development process and reduce total test costs.
Hardware Scanning
Maximizing throughput is a common requirement in automated test applications. To increase system throughput, many NI switch modules support hardware scanning. Hardware scanning improves throughput by downloading a list of connections to the switch modules and cycling through the list using an event (trigger) without any interruption from the host processor.
The most efficient method of hardware scanning is hardware-timed handshaking. In this process, the measurement device, such as a digital multimeter (DMM) or data acquisition board, issues a digital pulse after each measurement and thus triggers the switch to close its next connection in the scan list. After each scan list connection, the switch issues a reciprocal pulse that triggers the measurement instrument to take its next measurement. The cycle continues until the switch has scanned through the entire scan list. This process ensures optimal throughput because the entire measurement sequence is hardware-timed and has no additional software delays. Figure 3 illustrates this process.
Figure 2. Scanning facilitates hardware-timed measurements and increases throughput.
Predictive Maintenance
Armature and reed relays both have moving parts, which have a predefined mechanical lifetime. A typical armature relay, for instance, has a mechanical lifetime of 1 million cycles. This means that after the relay has been actuated 1 million times, it experiences an increased path resistance and potentially adds errors to the measurement.
To prevent downtime and increase efficiency, it is important that you replace the armature and reed relays in your system before they reach the end of their mechanical lifetimes. NI switch modules track and store the number of relay cycles onboard the module. You can use the relay count information to help predict when a switch module is near the end of its life. With this capability, you can streamline the process of identifying which relays you need to replace and avoid costly downtime.
Figure 3. You can extract relay count information using the NI-SWITCH API in NI LabVIEW software.
Similar function calls are available in text-based languages (NI LabWindows™/CVI, C++, or Visual Basic).
NI also offers several switch modules that use field effect transistors (FETs) and solid state relays (SSRs). Because these components have no moving parts, they have infinite mechanical lifetimes.
»See more information on FET and SSR switch modules.
Compliance and Safety
All NI switch modules are recognized by the appropriate certification bodies. Depending on the country, state, or principality, certifications may be necessary for use inside the region. For some certifications, such as CE, compliance can be tested in-house. For many modules, however, additional compliance testing by a third-party certifications body is required.
Figure 4. NI switch modules are always certified for their appropriate voltage levels.
All NI modules with voltage ratings greater than 60 VDC or 30 VAC and 42.2 Vp are considered high-voltage modules. These modules are certified by UL (and VDE or Demko, when necessary) to ensure they meet all safety regulations.
Superior Software Support
You can program NI switch modules using the free NI-SWITCH or NI-DAQmx APIs. These APIs are supported in various programming environments including NI LabVIEW and LabWindows/CVI, C, and Visual Basic. In addition to these basic programming APIs, NI provides a software programming package called NI Switch Executive, which you can use to abstract your switch programming and thus accelerate the development of your switch system. NI Switch Executive offers the following capabilities:
Aliasing: Dealing with thousands of channels without abstraction can be extremely confusing and time consuming. With the Aliasing feature in NI Switch Executive, you can name your channels and routes intuitively and thus simplify programming.
Graphical Configuration: The Graphical Route Configuration Utility for NI switches makes switch configuration a simple point-and-click operation. You use switch illustrations instead of text fields to create individual routes or route groups. Customizing the channel names and defining hardwired channels is also possible from this interactive utility.
Excel Integration: Using the import/export feature, you can export your virtual device to file and open it in Microsoft Excel. From there, you can edit your configuration and expand your channel count using the simple text-editing features and advanced formulas. When you are satisfied with your changes, you can import your configuration back to a new or existing virtual device. By leveraging the text-editing features of Microsoft Excel, you can save significant programming time.
Figure 5. NI Switch Executive adds abstraction and saves programming time.
In addition, NI Switch Executive simplifies your switch code maintenance through interactive debugging, validation, and reporting tools. You can deploy your NI Switch Executive configuration with NI TestStand test management software, the NI LabVIEW and LabWindows/CVI development environments, and Microsoft Visual Basic and C/C++. For more information on NI Switch Executive, visit ni.com/switchexecutive.
The mark LabWindows is used under a license from Microsoft Corporation. Windows is a registered trademark of Microsoft Corporation in the United States and other countries.