Electronic Data Collection and Analysis System
Yin Foo, Des; Foley, Margaret
E-Publications; PublicationNT; E-Books; Report ; 39/1992
Made available via the Publications (Legal Deposit) Act 2004 (NT).
Power and Water Authority
Report ; 39/1992
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Technical Report WRD92039 Viewed at 15:07:17 on 29/07/2010 Page 107 of 192. J I 44 Sll!nal Transmission There is no doubt that the pumped bore pressure transducer should not transmlt its signal uphole using analogue or frequency modulated voltage because of the probability of electrJcallnterference. The 4-20 rnA current loop will probably work though it is suggested that the PAWA e.xpertment with the AClFR's Mlndata system before accepting thts conclusion as fact. If a 420 rnA current loop Is not immune to Interference then some innovative thinking wi:'j be called for as there are no better alternatives on the market. Frequency transmission would probably be satisfactory for monitoring pressure transducer output Ln observatJon bores. with some reservations jf power lines are nearby. For the Westdata system. where logger and transducer are mounted together do'.vn the hole, it ts considered unlikely that there will be eiectrical Interference. for the frequency transmtssion is over a distance of about an Inch. If the flO1NIlleter is sulIic!ently far from the pump and if the link between it and its logger ts short, fn~quency trat1>,mtssion would probably be alrtgbt, though 4-20 rnA transmission would be safer. The S31lle holds for temperature and water qual!!y monitors. though here there seems to be little choice. Even for those Industrial type systems discussed In the previous sectlon that have a 4-20 rnA transmitter Into which the sensor plugs. the link between the sensor and the transmitter 'will not be current loop with the sole ec'<ceptlon of the Mlndata temperature sensor. Hence all sensors e.xcept this latter one cannot be placed down the pumped bor,~, and the link between them and the logger, or pOSSibly a current transmitter. should be kept short. Pressure Transducer T),l!J~ I suggest Mlndata pressure transducers for the pumped bore and the close observation bore. These units are accurate [though not quite as accurate as DrucksJ. and can be obtained as absolute transducers for ranges a2Om (ie. about a1Om water depth). 050m [I.e. about 0-40m water depth). 010001 (te. about O-gOm water depth) as well as other ,ranges. They are slightiy cheaper than Druck units and. being Australian made, there should b,! help available should any problems be encountered. Also. I am.lnlomled that Drucks come with a metre of vented cable whether or not the element is gauge or absolute; hence a way would have to be found ()[ Joining this vented cable to unvented cable (if an absolute system were choseni \Vithout permitting any electrical current or water leakage at the join.
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