What Are Switching Configurations?

Switches play a large part in expanding instrumentation channel count or increasing system measurement flexibility. For example, you can easily create a data-logging application with 100 channels using one digital multimeter (DMM) and a 100x1 multiplexer to the DMM -- this is much simpler and more cost-effective than purchasing 100 DMMs. However, you may find switch configuration choices challenging if you do not have some background on the topology types available. There are advantages and disadvantages to using each type of configuration in your automated test system.

For a look at the complete line of NI switch configurations, visit the Switch Product Selection Guide.

Matrix

Matrices are the most versatile type of switching module. You can connect any input to any output, individually or in combination. You can use matrix switches to route signals from oscilloscopes, DMMs, arbitrary waveform generators, and power supplies to various test points on a unit under test (UUT). The primary benefit of matrix switches is simplified wiring -- the overall test system can easily and dynamically change the internal connection path without any external manual intervention. Due to this flexibility, however, the cost of a full matrix test system can increase rapidly with the number of simultaneous connections required.

Understanding Switch Topologies
Creating a Large Switch Matrix
NI Matrix Switches

Multiplexer

Multiplexer switches are perfect for increasing the channel count of a single instrument. For example, you can use a multiplexer to connect a DMM or oscilloscope to many measurement points on a UUT or to connect an arbitrary waveform generator to several points needing excitation. With multiplexer switches, you can reduce your instrumentation costs while maintaining maximum system flexibility. A multiplexer is not as appropriate for systems that require many testpoints routed to multiple instruments. In that case, your ideal choice is a matrix.

Understanding Switch Topologies
Multimodule Scanning with National Instruments Switches
NI Multiplexer Switches

General-Purpose Relays

General-purpose switches consist of multiple, independent isolated relays. They can connect one input to one output and are commonly used to turn on or off devices such as motors, fans, and lights. For unique matrix or multiplexer configurations, you can externally wire several general-purpose relay channels together to make a matrix or multiplexer. Additionally, you can use National Instruments general-purpose switches, usually built with Form A or Form C relays, to switch high-voltage or high-current signals.

Understanding Switch Topologies
How to Choose the Right Relay
NI General-Purpose Switches

Relay Drivers

National Instruments relay drivers are the ideal choice when the current and voltage requirements for relays exceed those found in existing relay modules (or for relays embedded in a test system). Like NI switches, relay drive modules are controlled with NI-SWITCH driver software or NI-DAQmx measurement services software, so you can program external relays connected to the relay driver and standard PXI and SCXI switch modules identically.

Understanding Switch Topologies
Driving External Relays with National Instruments XX67 Switch Series
NI Relay Drivers

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