Matrix Switch Expansion Guide

A matrix is the most versatile switch topology. It is made up of rows and columns that can connect any input to any output. With a matrix switching system, you can connect several instruments to various test points on a unit under test (UUT). This capability can eliminate your need to duplicate instruments and thus reduce your cost to test.

Matrix Size

Matrix size is often described as M rows by N columns (M x N) configurations. Some common configurations are 4 x 64, 8 x 32, and 16 x 16. For information on multiple-wire (2-wire) switching and its alternatives, consult the Complete Switching Tutorial.

Because of its flexible architecture, a matrix is also easily inverted, whereby rows become columns and columns become rows. You achieve this simply by how you wire the matrix. For example, a 4 x 64 matrix can be made into a 64 x 4 matrix. This knowledge is especially useful in matrix selection, because it can save you time and money.

With some modules, you can partition a matrix into several smaller configurations within the module. For example, you can create dual or quad configurations, which respectively provide you with two or four smaller matrices in a single module. Some common examples of partitioned matrices include dual 4 x 32, dual 8 x 16, and quad 4 x 16 configurations.

See Also:
Complete Switching Tutorial

Terminal Block Configurations

With National Instruments matrix switch offerings -- NI 2501, NI 2503, SCXI-1127, SCXI-1128, and SCXI-1129 -- you can achieve several different 2-wire matrix configurations through the use of terminal blocks. The following table describes configurations you can readily achieve using the corresponding matrix module and terminal block.

Matrix Expansion

Matrix modules can also serve as building blocks for creating larger configurations that are well beyond the size of a single module. Connecting the rows of two modules doubles the column size. Likewise, connecting the columns of two modules doubles the row size. The following is a compilation of frequently asked questions (FAQs) in regard to expanding a matrix.

Matrix Switch Expansion FAQs

How do I determine the number of modules my matrix requires?
For the purpose of this example, assume your application requires a 21 x 50 matrix and that you have chosen to create it with 4 x 8 matrix modules. These are the steps:

Method 1:

1. Determine the matrix size of a single switch module. (4 x 8)

2. Divide the number of rows desired by the number of rows in a single module. Then round up the answer. (21 / 4 = 5.25) » 6 modules

3. Divide the number of columns desired by the number of columns in a single module. Then round up the answer. (50 / 8 = 6.25) » 7 modules

4. Multiple the values found in steps 2 and 3 to determine the number of modules required by your matrix. (6 x 7 = 42, which creates a 24 x 56 matrix)

Method 2:

1. Determine the matrix size of a single switch module. (8 x 4)

2. Divide the number of rows desired by the number of rows in a single module. Then round up the answer. (21 / 8 = 2.625) » 3 modules

3. Divide the number of columns desired by the number of columns in a single module. Then round up the answer. (50 / 4 = 12.5) » 13 modules

4. Multiple the values found in steps 2 and 3 to determine the number of modules required by your matrix. (3 x 13 = 39, which creates a 24 x 52 matrix)


How do I expand the number of rows?
Connect the columns of the modules to expand/increase the number of rows in your matrix. The following diagram connects two 4 x 64 matrix modules to create a single 8 x 64 matrix by connecting the 64 columns of each module.
How do I expand the number of columns?
Connect the rows of the modules to expand/increase the number of columns in your matrix. The following diagram connects two 4 x 64 matrix modules to create a single 4 x 128 matrix by only connecting the four rows of each module.
How do I physically expand the matrix?
You can physically expand any matrix by using individual wires to connect the terminals of one module to the terminals of another module, but this can become very tedious as your matrix size increases. For example, to build 128 x 16 matrix out of eight 16 x 16 matrix modules would require many hours to manually connect 224 wires. National Instruments addresses this cumbersome process by offering effortless matrix expansion solutions for the SCXI-1127, SCXI-1128, and SCXI-1129 matrix modules. You can connect multiple SCXI-1127/28 modules with expansion cables to expand both row and column count. An expansion cable carries four differential (2-wire) signals. To expand the columns of the SCXI-1129, you can use the same expansion cables as the SCXI-1127/28. You can expand the row count of the SCXI-1129 with expansion plugs, which connect the columns of two adjacent switch modules. With the expansion plugs, you can create a 128 x 16 matrix in less than five minutes.

Matrix Expanstion Examples

Example 1. Creating a 16 x 128 matrix with the SCXI-1129

Solution: You have several options to achieve this matrix configuration. Here are a few:

Example 2. Creating a 8 x 16 (2-wire) matrix with the SCXI-1127 or SCXI-1128

Solution: Each SCXI-1127/28 requires use of the SCXI-1332 (4 x 8) terminal block.

Example 3. Creating a 4 x 12 (2-wire) matrix with the NI 2501 or NI 2503

Solution: Each NI 2501/2503 requires use of the TB-2606 (4 x 6) terminal block

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