Modern automotive lighting uses arrays of high-power light emitting diodes (LED). They are dependable and much more efficient than traditional lighting which uses a single lighting element. A LED array typically holds about 10 or more individual LEDs. Together, they form the complete lighting element for the vehicle. Intensity and color tests on each LED in the array ensure uniformity in appearance and their functional specifications. Testing for these LED arrays requires multi-channel lighting analyzers. Test algorithms light up the LEDs according to their operational sequences and the analyzers capture each one for measurement.
Keysight i7090 is an automated inline test system that supports up to 20 parallel test core and runs on test software that is highly customizable. This allows you to create the lighting and test sequences you need for the LED array. The high number of parallel test cores allows you to test more boards at the same time to maximize production output. The test software includes a module that supports Feasa™ LED analyzers with simple, easy to use test steps. With this, anyone can create effective LED tests on the Keysight i7090.
LED testing is a powered test. In most cases, applying power to the board lights up all the LEDs. But sometimes, you may need to create some digital test libraries on the Keysight i7090 to drive the logic devices on the board to get the LEDs to turn on. Special light probe on the test fixture above each LED captures its light emissions and routes it to the input channels on the analyzer through optical fibers. Feasa™ LED analyzer comes in different channel count configurations, with the largest unit capable of supporting up to 20 channels. So, depending on the total number of LED you are testing, you may need more than one analyzer.
To create the LED test steps in your testplan, start by adding the analyzer units that you want to use to the i7090 test program. The example in Figure1 below shows multiple LED analyzers in the i7090 instrument panel. Each analyzer uses a unique serial communication (COM) port on the computer. All you need to do is to enter the COM port number and baud rate or data transmission speed.
Figure1: Keysight i7090 instrument panel adds multiple LED analyzers
Next, create the LED test steps in the i7090 testplan. The i7090 testplan starts with performing unpowered tests like opens/shorts tests and passive components measurements. A defect detected at this stage aborts the test flow as it is unsafe to apply power to the board with a defect. Only when all unpowered tests pass, the testplan will continue to the powered tests group.
Figure2 shows the available test steps for the LED analyzer. The “Capture” test step triggers the measurement of all channels on the analyzer regardless of whether that channel is in use or not. The analyzer stores the measurements in its memory until it receives the next capture instruction. Once the measurement is available, you can use the “Get” test steps to test the values with different units of representation. You can have a single “Capture” test step with a mix of different “Get” test steps depending on your preference in the testplan.
Figure2: LED test steps in i7090 testplan
Test steps that return color and intensity values.
- Get Hue. Saturation, Intensity
- Get R, G, B Intensity
Test steps that return color values.
- Get U’V’ Chromaticity
- Get Wavelength
- Get XY Chromaticity
The example in Figure3 below shows a “Get R, G, B Intensity” test step and its step settings. The test name and fiber number field in the test step settings link the channel number on the analyzer to the individual LED on the board like 1%LED100. This must match the actual fiber routing on the test fixture so that the test step is checking the correct LED on the board.
In the testplan, the LED test group begins with a “Capture” test step to trigger the measurement of an analyzer. The “Get R, G, B Intensity” step tests the measurement against a set of upper and lower limits. Limits can be set differently for each test step as well but for most cases, similar devices will use the same set of limits. In this case of Figure4, the testplan is checking for red on the LED as you can see that the expected value on red is significantly higher than the others.
Figure3: i7090 testplan with LED test steps
In setting the test limits, bear in mind that the LED tests in a production environment are different from the lab environment of the LED manufacturer facilities. The losses in transmission over fibers and ambient light sources interfere with the final measurement. Therefore, you may see a difference in measurement between production values and datasheet specifications. What is more important is the repeatability of the test measurement between test cycles and different boards. This decides how stable the test operation is and its ability to detect any outlier.
For more details on the commands and sequences for the control of the i7090 handler, you can refer to my earlier posts on Keysight i7090 with PTEM-Auto Mode. Also check out the series of posts on test automation with Keysight i7090 using PTEM to find out more.
You are welcome to contact me if you have any questions or comments.
Stay safe and happy.