Communications: electrical – Continuously variable indicating – With particular transmitter
Patent
1997-09-12
2000-01-04
Horabik, Michael
Communications: electrical
Continuously variable indicating
With particular transmitter
34087001, 34087016, 340603, 494 10, 494 27, B04B 1500
Patent
active
060114908
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an apparatus for measurement of the position of an interface between two fluids in a centrifuge rotor during rotation, comprising an electric or magnetic sensor mounted internally on a wall in the centrifuge rotor, and means for contact-free and intermittent transmission of measurement signals from the sensor to a stationary measuring unit outside the centrifuge rotor.
Of particular interest to this invention is measurement in centrifuges for the separation of fluids obtained when producing oil from subsurface formations, including offshore oil production. In many cases during such production there will also be obtained water and gas together with the oil. In centrifuges used for separation of the fluid fractions it is of great importance to be able to measure the level of the water layer and the oil layer in the centrifuge rotor, i.e. in relation to the interior wall of the rotor. A high degree of accuracy is desired in this level measurement, i.e. measurement of the position of the interface between the fluids or media. Specifically it is important to be able to measure the position of the interface between water and oil with high accuracy.
Accurate measurement of position or level in this connection has been found to be difficult however, because of sources of error and disturbance factors, perhaps in particular the fact that the level of the interface of interfaces in a centrifuge rotor during rotation, may vary somewhat such as in consequence of the through-flow of fluids in the axial direction of the rotor. Also other factors can have influence on the measurement, for instance a varying salinity of the water, capillary effect and so forth. These factors or circumstances may be influenced either in a favourable or in an unfavourable direction under the high acceleration forces to which the fluids are subjected in the centrifuges concerned, for example 3000 G. Another consideration of significance is the response time for the measurements, since quick changes of the interface level in the centrifuge rotor may require quick adjustment or other precautions from an operator or a surrounding system.
From Swiss patent specification 653,129 there is known a measurement apparatus as stated in the introductory paragraph above. This known apparatus, however, will not result in sufficiently accurate measurement as required according to the above discussion, especially not in view of the disturbing factors or circumstances mentioned.
Moreover reference can be made to German patent specification 2.914.423 relating to a sentrifuge with means for optical measurements through cells incorporated in the sentrifuge rotor. There are also shown indications outside the sentrifuge rotor for measuring or controlling the rotational velocity of the rotor.
What is novel and specific in the apparatus according to the invention in the first place consists therein that the sensor penetrates said interface, measurement values that are recorded during at least a portion of a revolution of the rotor, before said transmission of corresponding measurement signals to the measuring unit, and generator means comprising a stationary magnet near the centrifuge rotor and a coil mounted in the rotor so that a voltage is induced in the coil during movement past the magnet by rotation of the rotor, and the coil is connected to the electronic circuit.
A substantial advantage of the solution stated here, consists therein that the measurement can represent an average of level values over a portion of a revolution of the rotor or the container, or possibly several revolutions. This can be a fraction of a revolution, but normally in practice it will be convenient to transmit measurement signals to the measuring unit once for each revolution of the centrifuge rotor. The invention makes it possible to measure the position of the interface between water and oil with an accuracy at the order of magnitude of 0.1 mm.
As regards the basic principle of measurement in the sensor, this may be a capacitive measurement principle, as in
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Fallet Truls
Henriksen Per Scholberg
Tonnesen Harald
Exxon Production Research Company
Horabik Michael
Wong Albert K.
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