Using an NI PXI-Based Solution to Develop a Pipelined Test System for Proximity Sensors

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"With the implementation of an NI PXI-based test system that uses an NI USB device and LabVIEW software, we developed the test system faster and more cost-effectively."

- Carlo Philip Abuan, Global Inventive Technologies Int'l Inc.

The Challenge:
Developing a proximity sensor test system that achieves the fastest test time possible for test parameters including typical infrared (IR) LED parametric test, proximity sensing functionality tests, and I2C communication tests.

The Solution:
Using NI hardware and software to develop a functional test system specifically designed for proximity sensor devices.

Author(s):
Carlo Philip Abuan - Global Inventive Technologies Int'l Inc.

Basic Test Setup

Figure 1 shows a simplified test setup for the device under test (DUT), which is a proximity sensing device. This DUT is actually a complex device, but we can simplify it to just an IR emitter, an IR receiver, and a built-in I2C transceiver used for sending and receiving data and commands. The output data varies in direct proportion to the distance of the blocking material. The test setup requires varying the distance, d, then reading the resulting data through the I2C interface. The test procedure also includes verifying the IR emitter component’s electrical characteristics such as forward/reverse voltage, forward/reverse current, and luminous intensity. The test also includes verifying the response of the unit under various lighting conditions using an external light source with a different spectrum.

In this test setup, we have one source measure unit (SMU) to provide power to the device and test the electrical characteristics, and another SMU to measure the photo detector current and provide power to the light sourcing device. An I2C device is required to send data to the DUT.

The Test System Setup

The final test system configuration is comprised of an NI PXI-4130 power SMU, an NI PXI-6251 M Series data acquisition (DAQ) device, an NI PXI-2570 relay module, an NI PXI-8108 dual-core controller, and an 8-slot 3U NI PXI-1042 backplane. An NI USB-8451 I2C/SPI/SMBus interface acts as the the I2C interface. To improve the overall test time, we implemented the pipelining method on two test sites by doubling some of the components such as the power supply and the I2C module. Figure 2 shows the final configuration of the test system that has two sites being tested simultaneously.

At one site, the PXI-4130 provides power to the DUT and simultaneously measures the resulting circuit current. This same module is used as an SMU for measuring the electrical characteristics of the IR emitter part of the DUT such as the forward/reverse voltage and the forward/reverse current. The switching of this SMU is done via the PXI-2570 relay module. Another PXI-4130 power SMU is used either as a power source to activate the light sources or as a current measurement device for the photo detector circuit. Again, this is possible via the PXI-2570 relay module. The PXI-6251 measures low-voltage levels on some of the DUT pins. The same module also communicates to the custom auto test handler via the handler’s I/O communication port. The handler was designed to accept the voltage levels of the PXI-6251 for compatibility.

All the tester-handler communication protocols such as the start of the test, the end of the test, and the binning signals are done through the PXI-6251 digital I/O port. The USB-8451 reads and writes command data to the DUT. The 2.53 GHz PXI-8108 acts as the PC controller. This controller module acts as the brain for all the modules in the test system, including the I2C module. The tester software runs through this controller using the Windows OS. Each PXI module is securely inserted in a slot on the PXI-1042. Lastly, to double the test site, we simply doubled the SMU modules and the I2C module and shared the rest of the components.

The pipelining method has an automated test handler with two test sites. On the first cycle, the first DUT enters test site one and half of the test parameters are performed. Test site two is empty during this cycle. On the second cycle, the first DUT proceeds to test site two, which conducts the remaining half of the tests. At the same time, the second DUT enters test site one for the first half of the test parameters. On the third cycle, the first DUT leaves test site two and goes to its proper bin depending on its test results from both sites. At the same time, the second DUT enters test site two, the third DUT enters test site one, and the cycle continues. With this setup, the test time is reduced to half its single-site counterpart.

The Test Software

To control all the NI hardware and create the main tester software, we used NI LabVIEW system design software. All the necessary drivers are readily available because using both NI hardware and software eliminates any compatibility issues. The graphical nature of LabVIEW also makes it very easy to use and learn as compared to text-based programming languages, which require a person to memorize and learn the syntax. With LabVIEW, you don’t need to memorize any syntax; you just have to become familiar with the simple graphical environment.

The main test software GUI is shown in Figure 3. All the input information required for the tests is shown including the test parameters, test limits, lot information, username, data logging directory, and test file. The output is displayed in a tabular form showing the individual result of each test item. To distinguish between the results, parameters that failed are shown in red and parameters that passed are shown in black. Then, an overall indicator located on top of the table shows the overall test results.

In this GUI, you can also see the total number of units that passed and failed, the resulting yield, the binning allocation, the breakdown of failed parameters, and the current status of the tester and handler connection. All the necessary information for this project is shown but not limited to the items currently displayed; any additional indicators or controls can be added or removed as desired. Because the LabVIEW programming environment is quite user friendly, all of these changes can easily be made. Other functions such as data logging and data analysis are done in the background and are saved in a file with a tab delimited format.

Conclusion

National Instruments provided us with the necessary software and hardware to develop our pipelining test system specifically for proximity sensor devices. With the implementation of an NI PXI-based test system that uses an NI USB device and LabVIEW software, we developed the test system faster and more cost-effectively. The perfect compatibility of National Instruments hardware and software equated to faster integration and development. The software was also easy to use, which equates to less coding time. The hardware is light and compact and is simply plugged into a single chassis, which resulted in shorter hardware integration time and the additional bonus of a significantly smaller footprint. The modules are also much cheaper compared to available stand-alone counterparts in the market. Therefore, we built a reliable test system developed with the best software and hardware available, in the most time- and cost-effective manner possible.

Author Information:
Carlo Philip Abuan
Global Inventive Technologies Int'l Inc.
Mountview Industrial Complex, Bancal, Carmona
Cavite
Philippines
Tel: +6346 430 3617
Fax: +6346 430 3617
CARLO.PHILIP@FUJIMASTER.COM

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