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SENSA ELECTROMAGNETIC BOREHOLE FLOW METERS
1. Purpose and objectives
To measure the
vertical water velocities in boreholes. Exceptionally high
sensitivity down to 1mm/sec permits measurement down to true
Electromagnetic flow meters measure the velocity of water
or other aqueous fluid flowing over a sensing probe. The
measurement method uses the Faraday Principle of Electromagnetic
Induction, where a conductor moving in a magnetic field has
induced in it a voltage proportional to the
based on the SENSA-RC2 (see component C79.2.09), adapted
to measure the vertical velocity of water in boreholes. It may be
mains or battery powered, measuring flow velocity over the range
0 to 4 metres/sec, with resolution down to 1mm/sec. LCD display
of instantaneous or averaged
parameter is the velocity at the centreline of the borehole, and
the relationship between this measurement and the mean velocity
has been determined for a typical velocity profile in
boreholes from 80 to 400 mm diameter. To ensure correct probe
positioning, mounting rings to suit different borehole sizes can
The probe cable is tough polyurethane protective jacket, with internal Kevlar suspension cores to prevent stretching, and systems with cable lengths up to 300m have been supplied. The cable and probe are fitted to a suitable cable reel, with a flying lead to the control box.
Only manual cable reels have been supplied to date, but powered reels are possible.
temperature is - 5 to + 50 °C, and the control boxes are rated
along the axis of a centralised vertically mounted probe.
in metres/second of the average velocity in the borehole,
displayed on the internal LCD display and also transmitted as
an ASCII string from the RS232 output. Using depth information
from the cable reel, the velocity/depth graph can be plotted to
enable borehole yield from different levels to be determined.
5. Operational requirements and restrictions
For short cable lengths (< 50m), the instruments may be used by a single operator. With longer cables, at least two people are required for handling, and at 300m mounting on a vehicle is advisable. Velocity measurement is extremely easy, and little training is required for basic measurements. Training is suggested for mechanical handling of longer cable lengths. Instruments with cable length <60m may be powered by internal batteries, but longer cables require external power from mains or battery.
testing has been in boreholes with non-magnetic liners (usually
PVC). Operation in magnetic liners such as mild steel has not
been evaluated, and may affect
6. Form of presentation
specifications of the instruments are available.
7. Operational experience
been in use since 1996, with good results.
8. Originator and technical support
Services Ltd. England.
From Aqua Data
10. Conditions of use
Instruments are for sale direct from manufacturer or from agents.
|(First entered: 1 DEC 00||
Last updated: 1 DEC 00)