Electrical problems given the bird
Tom Shelley reports on a novel approach to fault finding in complex electrical systems
A low cost, hand held tool finds faults in any electrical system by only recording 'events' and their logical relationship to other events.
Only recording data likely to be relevant, as opposed to masses of mainly irrelevant information simplifies design, reduces cost, and helps identify problems more quickly.
David Mawsdley, managing director of Laplace Instruments, explains that the inspiration for the 'Birdie' FTR Fault Tracker came out of problems with the company's own central heating system at its offices in Norfolk. Over some two years, the heating system would sometimes fail to come on at is set start up time in the early hours of the morning, for no obvious reason. Plumbers failed to provide an answer and no suitable logging system could be found either in catalogues or on the Internet.
Seeing a market opportunity, as well as solving an irritating problem, the company came up with the idea of a fault logger that recorded on-off changes in up to 16 inputs. Patented circuitry converts all inputs to 2mA, regardless of whether they be 12VDC or 240VAC or anything in between. Events can be recorded whether they occur once in a month - the batteries run for 50 days or the units can be powered by the mains - or ten times in a second. Playback may be depicted on an LCD screen by running or stepping through the event sequence, or exported to a PC as an Excel spreadsheet. Safety is assisted by the ability to padlock the unit and also because fuses cannot be accessed unless all connections are removed.
The company central heating system problem was solved when the unit revealed that on days when the system failed to come on, the signal from the auxiliary contacts on the pump contactor was missing. This prevented the main burner circuit starting, hence no heat. On an automatic valve assembly machine, the unit showed that malfunction occurred when a momentary pulse from a proximity sensor was initiating an operation before its proper time. This only occurred when the machine was running at normal full speed due to centrifugal forces acting on a cantilevered mounting plate. Checking the operation of the sensor showed that its threshold adjustment had slipped. The units have also been used to discover the causes of occasional rogue operation in a rear thruster unit on a rig support vessel and an intermittent fault in the gate opening system on an unmanned railway level crossing.
Birdies are priced at just under £700 each and will be in the RS Catalogue from September 2003. The units are manufactured by Nemco in Stevenage, whose prices, Mawdsley declared, compare very favourably with quotations from companies based in the Far East.
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* Only logging on-off events and their logical sequence greatly simplifies the indification of intermittent faults
* Units can monitor up to 16 inputs at any voltage from 12VCD to 240VAC or 415VAC three phase in star.
* Occurrences can be studied by running or stepping through recordings or by exporting to a PC as an Excel spreadsheet
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