Common Switch Configurations for NI Modular Instruments

National Instruments’ offering of modular instruments provides a wide range of analog and digital devices used to build tightly integrated test and measurement systems. If an application requires a high-frequency or high-resolution measurement, there’s more than likely a modular instrument that will accommodate that need. However, systems often require several channels of input or output – how can this be addressed with modular instruments? Instead of measuring with several instruments, you can take advantage of the integration between NI switch devices and modular instruments for high channel count needs.

National Instruments offers a complete platform of switches to match measurement needs. For a complete list of NI switch modules, visit the Switch Product Selection Guide. To make configuring modular instrument systems even easier, each section below lists common configurations of modular instruments, both PXI and SCXI platform switches, and their accessories.

Note: Each listed switch is merely a recommendation based on common configurations. There are many variables that could be reason to choose a different switch. Please visit the Switch Product Selection Guide or the Switches Homepage for a more complete specification listing.

Digital Multimeters (DMM)

NI DMM devices provide very high precision voltage, current, and resistance measurements. NI DMMs are single channel devices, so a high-density multiplexer that will accommodate a large number of test points should be used to expand the channel count. In general, NI DMMs operate at a very high resolution and low frequency, so be sure to use a multiplexer that can operate in the desired voltage and current levels.

National Instruments currently offers several high-speed modular digitizers with bandwidths up to 100MHz. NI Digitizers do not usually require a high voltage switch. Normal operating range is around + - 10 V and doesn’t exceed 42 V. Expanding the 1-2 input channels into several high frequency inputs is the most common objective, so NI digitizers are usually combined with an RF switch to achieve this goal.

NI DSA devices offer high resolution, medium frequency measurements. All DSA boards use a +- 10 Volt input range, so bandwidth (as opposed to voltage/current specs) is the usually the most important specification to consider when choosing a switch for your modular DSA device. NI DSA devices have 2-8 analog inputs that can be simultaneously sampled. Using a matrix switch (or a multiplexer with several banks) will allow several test points to connect to each channel and take advantage of the dedicated A/D converters.

National Instruments signal generators are used for many purposes such as frequency sweeping and video generation. Each signal generator contains one channel and as a group their maximum frequency ranges from 8 MHz to 105 MHz. In most cases, any NI switch can handle the voltage level produced by an NI signal generator, so primarily look for a multiplexer that operates in the frequency range that your application requires.

As the name implies, frequency is usually the main consideration when looking for a switch to expand the channel count of your modular RF devices. NI’s switch offering includes RF multiplexers and matrices with a bandwidth up to 4 GHz.

National Instruments’ PCI/PXI-653x devices use standard 5 V TTL/CMOS input/output data lines with a transfer rate up to 20MHz. The PXI-655x devices include programmable voltage levels (-2.0 to 5.5 V) with a clock rate up to 100MHz. These specifications make it easier to expand channel count since every NI switch can operate within these voltage levels. Most applications utilize a switch with a high bandwidth so that the high speed digital instruments may operate at their maximum transfer rates.

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