Building Functional ATE for Irrigation System Controllers Using LabVIEW and NI PXI Hardware

For ATE systems, manufacturers must test the functionality of their products as quickly and efficiently as possible. In both single-component and complete-product testing, it is critical to test performance under conditions as close to “normal usage” as possible.

In addition, functional ATE testing involves the complex challenge of emulating human behavior, including operating knobs and buttons and reading screens. We wanted to integrate commercial off-the-shelf (COTS) technology into our ATE system to solve these challenges.

ATE System Development

We needed to build ATE for an irrigation system controller that could perform tasks such as pressing unit buttons, turning switches, and “reading” the messages displayed on an LCD. It also needed to measure electric parameters applied to the water valves that compose the irrigation system.

Using NI PXI hardware and LabVIEW graphical system design software, we designed an ATE system to interact with the unit under test (UUT) through firmware in its microcontroller. The ATE has a test head equipped with the following functional parts:

• Four pneumatic actuators to press the buttons
• Two pneumatic actuators to activate two sliding switches
• One gyratory actuator activated by a stepper motor for a circular switch
• One monochromatic camera
• A multiplexed current measurement system
• A complex mechanical and pneumatic system to reach the test points inside the unit

By simultaneously operating four buttons in the front panel while the UUT is being energized, the ATE activates the firmware. The NI PXI-6515 industrial digital I/O module controls the pneumatic cylinders and reads the position sensors. Once the UUT is in test mode, the ATE performs a series of activations on all the display elements in the UUT’s front panel and the vision system validates these activations by reading the messages displayed on the LCD.

The vision system consists of an IEEE 1394 monochromatic camera and optical character recognition (OCR) software libraries. Relays multiplex the outputs and an inductive transducer measures them. To measure the width of the pulses in a fast and reliable manner, we selected an NI PXI-6255 data acquisition module to read the output of the inductive current meter.

LabVIEW was the obvious choice for our system’s software for its easy-to-use graphical interface as well as its seamless integration with the system hardware. The LabVIEW program features three security levels to handle various critical functions such as the following:

• Test sequence changes
• Sequencer configuration changes
• Instrument diagnosis and adjustment
• Test program debugging

The LabVIEW application stores all the information from the real-time measurements in text files for traceability purposes. It also generates files in different and configurable paths to report the units that failed.

Meeting a Complex Engineering Challenge

By harnessing the power of the NI PXI platform and easy graphical programming in LabVIEW, we rapidly and efficiently built a complex, highly reliable ATE for irrigation system controllers. In addition, we were impressed with the fact that one compact PXI chassis can include and manage a variety of instruments. One digital I/O module and a control module for the step motor manage all the mechanical control, and the OCR vision system requires only one low-cost camera. Finally, by combining a high-speed data acquisition module with the powerful signal analysis and report generation features in LabVIEW, we developed an excellent solution for a complex engineering challenge.