Test time slashed from days to hours
An automated test stand measures the outputs of four oscillators at once and automatically cycles temperature and produces reports.
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 9/1/2003
A highly stable RF oscillator used in the Lockheed Martin Apache Longbow helicopter. The oscillator contains an analog input that makes small variations in the output frequencies; another analog input, used for built-in-test, adjusts output power. A digital output signal indicates a unit failure.
The challengeDevelop an automated test stand to measure the outputs of four oscillators at once and automatically cycle temperature, make measurements, and produce reports.
The tools- Advantest R3132 spectrum analyzer. www.advantest.com.
- Agilent Technologies 53310A modulation-domain analyzer and E4418B RF power meter. www.tm.agilent.com.
- National Instruments PCI 6025E multifunction data-acquisition card and PCI 6503 24-channel digital I/O card. www.ni.com.
- Tektronix PS2510G power supply. www.tektronix.com.
- VI Technology custom-designed analog multiplexer. www.vi-tech.com.
- Watlow temperature controller. www.watlow.com.
- Wenzel custom-designed RF multiplexer. www.wenzel.com.
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An automated system measures the outputs from four high-stability RF oscillators. |
Wenzel Associates (Austin, TX www.wenzel.com) developed a highly stable RF oscillator for the radar systems in the Lockheed Martin Apache Longbow helicopter. A functional test required Wenzel technicians to make several RF measurements over the temperature range of –55°C to +55°C, which took several days per unit. To cut test time and labor costs, Wenzel contracted with another Austin-based company, VI Technology (www.vi-tech.com), to develop an automated test system.
To achieve its frequency stability, the oscillator uses a heater element that maintains the oscillator's internal temperature at 65°C regardless of the external temperature. To test the oscillator, a Wenzel technician places it in a temperature chamber. When the DUT's external temperature is at the extremes of the –55°C-to-+55°C range, the test system's spectrum analyzer measures the frequency spectrum of the DUT's outputs and looks for harmonics at frequencies up to 3 GHz. The modulation-domain analyzer measures frequency stability and phase noise over a 1-min period while the power meter measures the oscillator signal's output power.
The test system uses two of the data-acquisition card's analog outputs and one analog input. One of the outputs, set from –5 V to +5 V, controls a tuning circuit that produces small variations in the oscillator's output frequency. Another analog output drives the unit's built-in-test (BIT) analog input. The data-acquisition card runs a test by ramping the BIT signal from 0 V to 5 V while the power meter measures the power of the 640-MHz RF output. When the power reaches a nominal level, the data-acquisition card uses an analog input to detect the logic level of the oscillator's digital output signal. When the system detects a change in logic level, it reduces the BIT voltage until the output power reaches a specified level and it again measures the oscillator's logic level, which verifies that the oscillator correctly set the bit.
The system uses two custom-designed multiplexers. VI Technology developed an analog multiplexer that switches the signals that connect the data-acquisition card and the power supply among the four DUTs. An RF multiplexer, designed by Wenzel engineers, switches the RF signals from the DUTs to the RF test equipment. The computer selects the DUT though signals from the digital I/O card.
ResultsThe automated test system, in operation since mid-2002, reduced test time from days to hours. Prior to development of this test stand, a technician would set up the DUT, let the temperature stabilize, and manually record the measurements from the test equipment. A complete test required several days and Wenzel could test just one oscillator at a time. Now, the system automatically sets the temperature at any time of the day. After the chamber temperature stabilizes, the system makes measurements on four DUTs and produces a report. A technician simply loads and unloads the DUTs from the chamber before and after a test.
