My aging vibration system started faulting. Shaking for 30 years takes a toll on a thing, after all. The system is pretty straightforward, just a big stack of audio amps and a controller. But I had been ignoring the warning signs and I recently have gotten my overdue comeuppance and the system finally tuckered out, it seemed for good. This is a bit of a sad sack story….but with a happy ending.
My bit-slicing days were few and far between (and far, long and away); I have always had a better sense of RF circuits and pipes and bursty lines on phosphor (or, now OLED), but my bliss in my quiet little anechoic chamber was about to be busted. My cell phone vibrated. Elmer was calling.
“Mike,” he started, “I hate to be the bearer of bad news, but the vibe table is down.”
My inner groan escaped over my gritted teeth. “What? It’s only older than my grown-up, graduated and working kids!” We bought the beast used and it lasted for 10 years.
“Well, it’s not starting and the amps are dying.” The original rig was composed of 20 4kVA Class D amplifiers, all ganged together and coupled into the electrodynamic shaker, which is really just a big speaker. The system is modest, by industry means, but it served us relatively painlessly for a decade.
After casting about for a few weeks, sending pleading messages around the industry, dispatching the dead boxes to various coasts, we got nowhere. The last guy who touched the design probably retired in the 90s and the design was definitely pre-CAD, pre-FPGA and, well, in modern electronics terms, pre-historic.
But, although this story does not really end well, we decided, as engineers, we could try to fix the thing, or at least give it the old college try.
The one thing that these vintage pieces came with—and I do not know how much the “art of the technical manual” still exists—is a wonderful, almost, lovingly written manual, still coupled to its cracked three-ring binder. The prose explained the theory of operation—almost tinged with a bit of remarkableness about the beauty of switched-mode circuits.
The core of the function of the thing was to create a 78 kHz pulse-width (PW) modulated signal that drove both the DC-DC conversion frequency for the amps and the PWM heartbeat, modulated by the drive signal from our vibe controller. This was piped out through some serious low pass filtering, which was used to trim out the harmonics. The whole thing is about efficiency. The Class D operation means that the power transistors (another story there) are either fully “ON” or “OFF.” In the ON state, they conduct with very little output resistance, hence the low loss (as opposed to a Class A amp which is always biased a bit and spends its time in the linear region where the losses are high).
Readers of Signal Integrity Journal might be bemused by the curvaceous layout of the PCB. At these frequencies, one need not worry about matching, characteristic impedance, skew, timing, or reflections. From a quick look at the board in the figure, it is apparent that the propagation of the signals is as lazy as a Sunday stroll at the market. The “logic” of the circuit was a mix of op-amps, AND, NAND, NOR, and other gates, stitched together such that any error in the critical parameters returning from sensors in the table buzzed a whiny alarm and the system would not run. No EPROMs or microprocessors here, just a cascade of 1s and 0s driving the table. For this analog guy, who has not looked at a logic truth table, well, maybe since this thing was put together, it was a sometimes fun/sometimes aggravating process of doling out digits in the circuit and figuring out how the logic worked.
Anyway, needless to say the designers of this beauty took great pride in the layout. One can almost imagine the scrape of an Exacto knife, trimming the mask, and, as you can observe, lots of test points! No fancy-schmancy error codes or indicators, just a set of DIP switches to isolate the errors.
One of the challenges of this project was re-populating the CMOS DIPs (the lucky thing is that everything is socketed). Replacement parts are dwindling and finding the right parts is the Internet equivalent of hunting around in your nutty uncle’s dusty attic. But! Parts can be found and swapped out. If there was any “fun” in this exercise it was puzzling out the circuit and bringing the logic back to life with a fresh 4043 Quad State R/S latch.
Anyway, in the end, the dinosaur was finally deemed extinct and a shiny new beat was put on-order. But in retrospect, the experience refreshed my understanding of the logic, and importance, of the lowly XOR gate.
How would your cell phone perform at -85 degrees Fahrenheit, after being subjected to hurricane winds and rain, followed by violent shaking similar to forces uses in space? Washington Labs could show you, but it might not be pretty.
Before many manufacturers ever put certain products on the market, there are standards they must meet. When the U.S. Armed Forces wants to take a product in the field that is mission-ready, they rely on a full-service testing facility like Washington Laboratories, Ltd in Frederick to simulate high altitudes, extreme heat, turbine wind and more. This kind of reputation for “finding what doesn’t work” helps product manufacturers make their products better, and safer.
A young Mike Violette was always fascinated with science and engineering and how the universe and things worked. This evolved into an interest in solving technical challenges. Mike began his career with his father and grew Washington Labs from a two-man consulting company to over 50 people in North America, Asia and Europe. continue
Dr. Gerry Hayes, of the Wireless Research Center and Mike Violette, of Washington Laboratories and ACB
Dr. Gerry Hayes, President and CEO of the Wireless Research Center and Mike Violette, CEO of Washington Laboratories and Director of ACB have signed a Memorandum to expand cooperation in wireless testing and measurements, during the attendance at the recent IEEE Wireless Wearables & Medical Interoperability Workshop (WAMI ’18) in Rockville, MD.
The Wireless Research Center (WRC), located in Research Triangle Park, North Carolina, is a CTIA & Verizon authorized test laboratory and features design services for radio frequency and antenna design. One of the unique features that this cooperation offers is over-the-air testing (OTA) which is critical for measurements supporting the deployment of the Internet of Things (IoT) and devices that support Machine to Machine (M2M) connectivity. Mike says “I’m pleased to have access to these unique RF capabilities as we work to build out our wireless services. RF circuit analysis and design are key services. In addition, the WRC offers propagation analysis that will be useful for site planning and radio frequency coverage for network planners.”
Washington Labs provide device certification testing for commercial, aerospace, consumer and defense clients. “Washington Lab’s capabilities provide our clients with full-service measurements solutions for EMC, Safety and Environmental requirements.” Gerry stated. “We’re looking forward to cooperating on education and outreach activities in addition to working on some testing projects and global certifications through ACB.”
Desmond Fraser, Director of ACB said that “The cooperation with the Wireless Research Center is another solid step for ACB’s capabilities expansion. With their resources, we can provide added value for our domestic and global certification customers.”
The agreement covers core competencies that combine the three organizations’ strengths, notably:
Design, Testing and Training for:
FCC, MIL-STD, RTCA DO-160, CE
Performance & Forensic
Shielding & Facilities
CTIA & Verizon Authorized OTA Lab
Pre-Compliance Testing & Mitigation
Field Testing & Propagation Modeling
Iot & Wearable Design Support
Antenna & RF Design
Simulation & Analysis
Engineering & Development
Certification for the United States & Canada
Notified Body Services for the European Union
Hong Kong OFCA Certification
The agreement, effective immediately, was inked April 30, 2018.
Considering military sales for your LED lighting products – many elements are evaluated through the process. This article provides some basic guidance but remember that some specific applications may include very specific evaluation methods. Consider the discussion here – please contact us for your specific needs.
Real estate limitations placed a Proton Therapy Center (PTC) near a Magnetic Resonant Imaging (MRI) facility creating a high risk of interference. The PTC uses a 9T magnet that moves and an 11 kW RF transmitter operating at frequencies sensitive to the MRI operation. The unique approach to providing isolation, developed by Washington Laboratories was documented and published by the Journal of Proton Therapy under the title of:
BY MIKE VIOLETTE
Reproduced with permission of IN Compliance Magazine
Original publication June 2015
HAPPY BIRTHDAY, NATIONAL BROADBAND PLAN!
Blow out the candles, already! The recent auction of Advanced Wireless Spectrum raised $41 Big Ones (that’s $41E9) for the US Treasury. Now, spectrum is a little like real estate and as Will Rogers once said: “I had been putting what little money I had in Ocean Frontage [because] they wasn’t making any more…” If there were spectrum futures, I’d recommend placing a buy. AT&T, apparently, thinks the same way, having dropped nearly one-half of the record bids.
Part of this haymaking for the Feds is the result of the FCC’s “National Broadband Plan” or “The Ominbus Broadband Initiative.” In 2010 the FCC released a plan to increase the availability of spectrum for broadband deployment in the United States. Some of the initiatives have had an immediate impact. Others have languished or have been overtaken by events. What has happened since is that the Commission has made hundreds of MHz of spectrum available for all kinds of mobile, IoT and M2M uses. This has caused some difficulties for incumbent users and created opportunities for innovators.
This article will provide an update of how the plan is being implemented.