Electronic Data Collection and Analysis System
Yin Foo, Des; Foley, Margaret
E-Publications; PublicationNT; E-Books; Report ; 39/1992
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Power and Water Authority
Report ; 39/1992
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Technical Report WRD92039 Viewed at 15:07:17 on 29/07/2010 Page 39 of 192. 'The magnitude of the variations (ie. the "scatter") due to physical vi:::Jrations which may be detected also depends on the logging system. The scatter was large for systems which take instantaneous readings (including Mindata, Torrens I Unidata), but much less apparent for the Wesdata system. This is a virtue of the Wesdata logging system which effectively avera'Jes a reading over a full second. Figure 3.7 is a compar.ison of the logged data types monitoring pumped bore drawdown. 'rhis .is explained since most transducers convert varying pressure to resistance, which is then conveted to a signal. In the case of 4-20mA transducers, the current is sampled almost instantaneously (about 300 microseconds) by the logger. However the \iesdata transducer converts the resistance to a frequency signal which is "counted" by the logger over one second. i't number of set-up configurations were separately investigated to reduce the effects of the pump vibrations including : (i) Placing the transducer at different depths relative to the pump ( from 2m below the inlet to 4m above it ), (ii) perforating the transducer conduit, (iii) Centralising the pump column, (iv) Elect:ric Filtering which involved adding a capacitor and coil to the transducer/logger circuit and (v) Physical filtering which involved the installation of a fine mesh on the transducer as a buffer. The confi.gurations above were trial led and did not indicate that any particular technique significantly reduce the scatter of logged water level data from the pumped bore.