433. Voltage disturbance problems with paper mill
The paper machine process requires precise control of the paper sheet tension as it progresses through the machine. On Caledonian Paper’s paper machine this is achieved by controlling 23 separate DC variable speed drives, which are inherently vulnerable to voltage disturbances because of problems with the control of thyristor firing.
Firing angle control has difficulty following the voltage change, with possible consequential damage to thyristors. To prevent this damage, it is common for drives to be equipped with protection that trips the drive, using settings dependent on the drive’s sensitivity to voltage disturbances, The manufacturers designed Caledonian Paper’s drives at 90%, so that disturbances below this level for more than a few cycles caused a trip.
It was confirmed that the paper machine could be affected by voltage disturbances of only 10% variation from normal (90% retained) and as for as little as 100ms. Some events, which have affected production, only just come into the classification of a voltage dip, as described in the European Standard EN 51060, and the severity of events which cause disruption is not severe when compared with all possible disturbance events under equipment testing specifications, as described in IEC standard 1000-4-11 (now IEC 61000-4-11 – Editor). However, as a result of the voltage disturbance and associated DC drive trip, the paper machine suddenly stops in an uncontrolled manner with the potential for extensive damage particularly, in the wire and press sections.
The possibilities of damage and extensive downtime are greatest within the paper machine but disturbances can also affect the rest of the mill with activities downstream from the paper machine, such as the coater, supercalandars, and ancillary equipment suffering to varying but lesser degrees. The situation can also be exacerbated by having multiple incidents in a relatively short timeframe, e.g. a number of events over one day, especially when followed by a succession of disturbances over a period of several days.
(Extracted from “Special Feature: Electrical energy storage,” IEE Power Engineering Journal, June 1999, pages 154 and 155.)
434. Wendy’s restaurant interferes with satellite system
The FCC’s Kansas City office received a complaint that the Search and Research Satellite Aided Tracking (SARSAT) system was experiencing interference from an unknown source. SARSAT is used by search-and-rescue teams to locate the radio beacon transmitters of crashed aircraft and distressed ships. Using mobile direction-finding gear, the FCC tracked the interference to a (presumably malfunctioning!) video display unit at a Wendy’s restaurant.
(From “FCC’s CIB Fight Interference,” Newswatch…EMC, Compliance Engineering European Edition, September/October 1995, page 8.)
435. Cellphone interferes with ECG
Trigano et al, in [5] report an electrocardiogram recorded during 1800 MHz cellular phone ringing with high amplitude and high-frequency artefacts that appears 3 seconds before the first ringing tone and that persisted until end of ringing. As consequence of these facts many hospitals have prohibited the use of cellular phones in some areas.
[5] Alexandre Trigano, Olivier Blandeau, Christian Dale, Man-Faï Wong and Joe Wiart “Risk of cellular phone interference with an implantable loop recorder,” International Journal of Cardiology, In Press.
(Taken from “Medical Equipment Immunity Assessment by Time Domain Analysis,” Mireya Fernández-Chimeno, Miguel Ángel García-González and Ferran Silva, 2007 IEEE International Symposium on Electromagnetic Compatibility, 8-13 July 2007, Honolulu, Hawaii, ISBN: 1-4244-1350-8, IEEE EMC Society.)
436. Safety while swimming in a sea of electromagnetic energy
In this issue of Mayo Clinic Proceedings, 3 articles bring the issue of exposure to electrical transmissions and patient safety to the forefront. Tri et al1 report on their investigation of possible cell telephone interference with medical equipment in a hospital setting. Gimbel and Cox2 provide a report of 2 patients with implantable cardioverter defibrillators (ICD) who had adverse interactions with electromagnetic scanning devices in their community. Finally, Austin et al3 report on a person whose consumer electronic device interfered with an electrocardiogram (ECG) and led to an initial misdiagnosis of atrial flutter.
The current investigation by Tri et al1 is a follow-up to their previous 2005 in vitro report.4 In their earlier research, the authors discovered that cell phones produced interference in 44% of the tested devices, although the incidence of clinically important interference was only 1.2%. Older analog cell telephones that emit a relatively high-energy signal produced the most interference. Cell telephones had to be placed fairly close to the tested device (ie, <33 in) to produce any interference. Cell telephones were less likely to cause interference in newer medical technology. The authors concluded in 2005 that technologic advances had improved the resistance of medical devices to interference from cell telephones, but that the type and number of electronic designs were anticipated to steadily change, necessitating ongoing testing.
Tri et al heeded their own advice and tested newer technology, using a study design more relevant to daily patient care. Specifically, in the current 2007 report, they investigated cell telephone and wireless handheld device (Blackberry, Research In Motion, Waterloo, Ontario) interference of medical equipment while the equipment was being used on hospitalized patients, including those in intensive care units. The tested medical equipment was both diagnostic and therapeutic (e.g. physiologic monitors, infusion pumps, mechanical ventilators). The authors performed 300 tests of cell telephone interference and 40 tests of wireless handheld device interference. They found no interference with any of the tested medical technology. The authors concluded that institutions should consider revising hospital policies that restrict cell telephones.
In contrast, Gimbel and Cox reported on 2 patients having ICD devices that were triggered by electronic article surveillance (EAS) systems (ie, electronic devices placed at store exits to detect stolen merchandise). In both cases, the patient had relatively close contact with an EAS device at a retail store exit. In one case, when the patient collapsed after being shocked, an employee propped the patient against the EAS pedestal, thereby triggering further shocks. In both cases, the patients had ICDs from the same manufacturer. Austin et al reported on a similar but less dramatic electrical interference event. A healthy volunteer had an ECG recorded as part of an extra-hospital drug study. The ECG was read as atrial flutter with an atrial rate of 333/min. It was discovered that the volunteer had a portable compact disk (CD) player (Walkman, Sony Corp, Tokyo, Japan) close to the right-arm lead of the ECG. When the CD player was turned off, the ECG recording returned to normal sinus rhythm (also see Banana Skin number 422 – Editor).
(Extracts from: “Safety while Swimming in a Sea of Energy,” Editorial, Mayo Clinic Proceedings, March 2007, Volume 82, Number 3, pages 276-277.)
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.
