404. Household heaters turned on spuriously by interference
The Japanese National Institute of Technology and Evaluation has announced that they have confirmed that some of the household electrical heaters available in Japan malfunction when subjected to electrical disturbances. They conducted the evaluation as a response to the information from consumers that electrical heaters sometimes turned themselves on. They tested thirteen models of heaters for immunity to EFT/B per IEC 61000-4-4. The test results indicated that four of the thirteen samples tested turned themselves on at test level 4 (4kV), and one of them had been caused the malfunction even at test level 1 (0.5kV)!
They also found that two of the thirteen samples could be (unintentionally) controlled by infrared remote controllers for audio/visual products. Fortunately, it seems no fire accidents had been caused – at least at the time of the announcement.
(Sent in by Tomonori (‘Tom’) Sato, February 2007. Never trust a software-controlled power switch unless it fully complies with all relevant parts IEC 61508. Also see Banana Skin No. 307.)
405. The EM environment in space 200 nautical miles up
The levels of electromagnetic fields that illuminate a satellite, that originate from earth-based sources, now exceed hundreds of volts per meter (V/m). It is pointed out that the electronic circuitry will have to survive these fields and remain operational as well.
MIL-STD-461E (table 1B) requires a space system to be compatible with high external EME levels of 100V/m from 100MHz-1GHz, but Figure 1 indicates that external fields at 200 nautical miles (nm) height due to earth-based sources such as radio, TV and radars occur out to 100GHz, and up to 250V/m. The field strength at 100 nm will be twice as high.
In a worst-case scenario these sources might cause damage to the on-board electronic devices.
It is also pointed out that EME can be coupled into a system even if it is not operating. Accordingly, a radiated susceptibility test without power applied would be a prudent step to consider.
406. Interference problems with the NASA Mars Reconnaissance Orbiter
Because of the selected science experiments, the RF communications link, and the limited space for these elements, the MRO spacecraft had greater than usual EMC considerations. Added to that, the late delivery of some of the hardware prevented early identification and resolution of EMC problems. The problems as identified during the test program are identified as follows:
The Electra (UHF) receiver was bothered by: SHARAD transmitting, mostly with ELECTRA uncoded, this was an effect that had not been predicted; MCS with its clock on caused ~8 – 10dB interference; MARCI caused ~3dB interference that had not been predicted.
The Shard radar (15-25MHz) was bothered by the C&DH, and its cabling to the power distribution unit and the pyro initiation unit. The basic source was its 24MHz clock, but other frequencies contributed as well.
(Work to resolve these problems was not completely successful in all cases, see the full paper for details – Editor) The spacecraft EMC performance is expected to be adequate for mission needs, but the work to accomplish this status was late, and not as certain as required.
(Extracted from: “The EMC Program for NASA’s Mars Reconnaissance Orbiter,” Albert Whittlesey et al, IEEE 2006 International EMC Symposium, Portland, OR, USA, August 14-18 2006, ISBN: 1-4244-0294-8/06.)
407. Power quality problems easily solved at bulk mail centre
The New Jersey International & Bulk Mail Center (NJI-BMC), one of the largest United States postal facilities, recently faced a dilemma regarding its six aging 300kVAR capacitor banks in its three load centers. Initially, we explored the possibility of replacing all capacitor banks on the system, because one of the cans overheated and subsequently failed. But the solution was as simple as turning them off.
Seven months ago, one of the six 300kVAR capacitor cans at the facility developed a bulge. Within a month, we replaced it. At that time, our maintenance crew noticed indicating lights on the other capacitor banks were lit. We presumed the remaining five banks would fail, and thought the simplest remedy would be to replace all six at once. An engineer quoted us approximately $30,000 for replacement, including labor, material, and testing.
A Surprise Solution. At this point, we realized that lower kVA loads coupled with the existing 300kVAR fixed capacitor banks on each side of the facility had caused the overheating and bulging of the capacitor can. Our preliminary calculation indicated the caps were resonating at 7th and 9th harmonics. After testing this load center, we connected power monitoring meters to all remaining load centers. The data revealed the fixed capacitors (if turned on) were creating higher THDs on the system. Later, we learned these fixed cap banks could also damage our supply transformers and equipment. Our solution was to simply turn the cap banks off. By doing this, we prevented a major transformer failure on our system and avoided lost production time.
(Extracted from “Bulk Mail Center Avoids Transformer Catastrophe,” EC&M, Jan 1, 2001, by Dilip Pandya.)
Russ O’Toole, chasing overheating in a Class D power, amp hung a scope on the output and found several volts in the MHz range. Not surprisingly, it was wiping out much of the AM broadcast band (MW to our European members). The manufacturer didn’t think it was a problem. The FCC did, and shut them down.
(From Jim Brown, on the SC-05-05 mailing list, 7 Dec 2006 15:27:43.)
Plans to send robots equipped with cameras and other sensors into dangerous environments such as burning buildings ahead of human rescue teams could be heading for trouble. More than two-thirds of systems involved in a large-scale trial in the US lost contact with their operators due to radio interference.
Of the 14 types of robot involved in realistic training scenarios, 10 experienced communications problems as a result of interference from other systems. According to the researchers, sticking to industrial, scientific and medical frequency bands designed to minimise interference between different systems is no guarantee of flawless communications between a robot and its operator. (But that’s not what the ISM bands are for! – Editor.)
Interference was a problem whenever the frequency being used became crowded or when one user had a much higher output than others. For example, transmitters in the 1760MHz band knocked out 2.4GHz video links, while a robot using an 802.11b signal (colloquially known as Wi-Fi) in the 2.4GHz band overwhelmed and cut off another that had been transmitting an analogue signal at 2.414GHz.
NIST has suggest a number of ways of tackling the problem, including changes in frequency co-ordination, transmission protocols, power output, access priority and using relay transformers to increase the range of wireless transmissions. (It sounds as if they could also benefit from some good old-fashioned RF design in their hardware, too! – Ed.) In a paper presented at last month’s International Symposium on Advanced Radio Technologies in Boulder, Colorado, they also suggest establishing new access schemes of software-defined radios that improve interoperability.
(Extracted from: “Rescue robots hit comms snag,” IET Engineering & Technology, April 2007, page 12. This item is also mentioned briefly in New Scientist, 10 March 2007, page 25. We should worry about this – military and security agencies are keen to use robots to avoid exposing their operatives to risk, and these robots will be armed and even autonomous – able to decide for themselves what to do. See IEEE Spectrum March 2007 page 12, “A Robotic Sentry for Koreas’ Demilitarized Zone.”)
410. ESD interferes with Japanese lifts
On a recent visit to Japan, Dave Imeson, secretary of the very successful and influential EMC Test Laboratories Association, was intrigued to find an electrostatic discharge plate installed near every lift button, with instructions to touch the plate to discharge any electrostatic charge before pressing the button to call the lift.
(Conversation during a break in the IET’s “EMC and Functional Safety” Working Group meeting on 9th March 2007, London U.K.)
The regular “Banana Skins” column was published in the EMC Journal, starting in January 1998. Alan E. Hutley, a prominent member of the electronics community, distinguished publisher of the EMC Journal, founder of the EMCIA EMC Industry Association and the EMCUK Exhibition & Conference, has graciously given his permission for In Compliance to republish this reader-favorite column. The Banana Skin columns were compiled by Keith Armstrong, of Cherry Clough Consultants Ltd, from items he found in various publications, and anecdotes and links sent in by the many fans of the column. All of the EMC Journal columns are available at: https://www.emcstandards.co.uk/emi-stories, indexed both by application and type of EM disturbance, and new ones have recently begun being added. Keith has also given his permission for these stories to be shared through In Compliance as a service to the worldwide EMC community. We are proud to carry on the tradition of sharing Banana Skins for the purpose of promoting education for EMI/EMC engineers.