The designer who automates tests

An exclusive interview with a test engineer.

Martin Rowe, Senior Technical Editor -- Test & Measurement World, 5/1/2011 12:00:00 AM

Read more "Test Voices" columns. Read more from the May issue.

Kenneth Schnebly is an analog and digital controls engineer at AML Communications, a maker of RF/microwave amplifiers for military applications. When he’s not designing RF amplifiers and their internal control circuits, Schnebly is automating measurements for both engineering and production. Senior technical editor Martin Rowe spoke with Schnebly at his office in Camarillo, CA.

Q: What kinds of tests have you automated?
A: Our tests include S-parameters, power, VSWR [voltage-standing wave ratio], 1-dB compression points, second- and third-order intercepts, and noise figure. The frequency range is typically 1 GHz to 18 GHz, but we increasingly get requests for amplifiers that run at frequencies up to 40 GHz. We also perform a range of specialized tests per customer requirements, both on the bench and using an ATE [automated test equipment] system that I developed.

Q: What’s in the ATE system?
A: The test system consists of a network analyzer, a spectrum analyzer, a power meter, a signal generator, an RF power meter, and a noise-figure meter. All instruments connect to the amplifier under test through a switching system. All equipment runs under software control over GPIB. We use the spectrum analyzer to measure power at specific frequencies and through frequency sweeps. We need better accuracy for measuring power levels at a specific frequency when we measure the amplifier’s 1-dB compression points. That’s then we use the RF power meter. For gain, phase, and VSWR measurements, the ATE system uses the network analyzer. The ATE system connects to the company network so we can download test data.

Q: What kind of specialized tests do you perform?
A: One customer wanted to us to measure a broadband amplifier’s in-band and out-of-band second-order harmonics. We made the measurements with a spectrum analyzer with the frequency increasing from a baseline in 100-MHz intervals. The spectrum analyzer made the power measurements as the signal generator’s output frequency increased. Because the tests required just two instruments, we performed the tests at the technician’s bench.
Another specialized test requires us to match, within a tolerance, the phase shift of amplifiers across a production run. A technician has to look at phase, gain, and other parameters while adjusting the amplifier to bring phase shift into tolerance. Of course, adjusting for phase shift causes other parameters to change, so we must find the optimal setting for all parameters.

Q: How has automation improved your testing?
A: A full suite of production tests, performed manually, required an hour of a technician’s time. Through automation, we reduced test time to between 3 min and 5 min. When I first set up the ATE station, I used test routines that engineers at Agilent Technologies provided. That was enough to get started. Using those routines, our test times ran between 8 min and 10 min. Over time, I modified the code, which reduced the test time to between 3 min and 5 min, with improved measurement accuracy.

Q: How did you become the automation engineer?
A: A few years ago, management saw that in order to stay competitive, we had to automate our testing and production, so I was asked to develop an automated test system. At the time, I lacked automation experience. During the process, I gained the skills and knowledge necessary to create automated systems and have since moved beyond just manipulating the ATE system. Today, I create different specialized systems. As a result, my company can test higher volumes in less time. T&MW

---

Interested in being interviewed for a future issue? Contact Martin Rowe.