In the world of Test & Measurement Automation, a turnkey test system may have tens, hundreds, or even thousands of individual signals or signal pairs that need to be verified during a test. Switching and multiplexing are common ways to change a system's hardware configuration by routing signals between the device under test (DUT) and a measurement device and/or power source to perform several different tests without having to manually disconnect and reconnect the signals.
What is a Switch Matrix?
A switch matrix is a controllable hardware module that is comprised of switches organized into rows and columns that form a node or cross-point where each x-line (column) and y-line (row) meet. A switch matrix follows the matrix schematic, as described in documentation from National Instruments. A sketch of a 10x6 switch matrix is shown below:
As you can see, the 10x6 matrix gives a total of 60 cross-points where each cross-point is an intersection between an x-line and a y-line. These cross-points can be energized to connect an x-line to a y-line or x-lines to other x-lines. This example shows a 10x6 matrix, however, switch matrices come in many different varieties and sizes. For example, Pickering Interfaces offers PXI(e) / LXI / PCI matrices that vary by electrical ratings (current and voltage ratings) and number of crosspoints. To get a sense of the scale which is possible, a single high-density matrix can have more than 1,000 x-lines with over 4,000 cross-points! When specifying a switch matrix for your application, it is important to have a clear understanding of the maximum number of signals a system may need for a given test system along with the system's electrical characteristics.
Connecting X-lines to Y-lines
For example, energizing nodes (9,2) and (10,1) will create a connection between X9 and Y2, and another connection between X10 and Y1.
Connecting X-lines to X-lines
Similarly, energizing nodes (1,1), (2,2), (9,2), and (10,1) will create a connection between X1 and X10, and another connection between X2 and X9.
Example test system hardware
Consider a DUT that has four data signal outputs and one power input. The test sequence required for this system is as follows:
- Step 1: Connect DUT to power source.
- Step 2a: Measure DUT Signal 1 with Measurement Device A.
- Step 2b: Measure DUT Signal 2 with Measurement Device B.
- Step 3a: Measure DUT Signal 3 with Measurement Device A.
- Step 3b: Measure DUT Signal 4 with Measurement Device B.
- Step 4: Disconnect DUT from power source.
A test system that is capable of performing these steps may look something like this:
Where each of the required hardware connection steps are shown below.
Step 1 - Connect DUT to power source
Connect the DUT to the power source by energizing relays (9,2) and (10,1).
Step 2 - Measure DUT Signal 1 and Signal 2
Connect Measurement Device A to Signal 1 by energizing relays (1,6) and (2,5).
Connect Measurement Device B to Signal 2 by energizing relays (3,4) and (4,3).
Step 3 - Measure DUT Signal 3 and Signal 4
Disconnect Measurement Device A from Signal 1 by de-energizing relays (1,6) and (2,5).
Disconnect Measurement Device B from Signal 2 by de-energizing relays (3,4) and (4,3).
Connect Measurement Device A from Signal 1 by energizing relays (5,6) and (6,5).
Connect Measurement Device B from Signal 2 by energizing relays (7,4) and (8,3).
Step 4 - Disconnect DUT from power source
Disconnect the DUT from the power source by de-energizing relays (9,2) and (10,1).
Why use a switch matrix?
A switch matrix is used in a test system to connect and disconnect multiple devices to and from each other automatically, often during a test sequence. For complex automated test equipment (ATE) racks that utilize multiple test devices and DUTs, a switch matrix can reduce cycle time and the amount of manual setup that would otherwise require an operator.
Conclusion
A switch matrix is a versatile piece of hardware that can help maximize an ATE's efficiency by changing the hardware configuration during an automated test. If a test workflow has a high signal count and requires manually connecting and disconnecting signals as part of the test, consider employing a switch matrix as part of your test system.
For examples of case-studies which use a switch matrix, check out the links below:
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