FR2564969A1 - System for hydrostatic measurement of the level of liquid, such as recording tides, capable of being periodically calibrated by comparison with columns of liquid of the same nature acting as a reference assuring millimetre accuracy and reliability - Google Patents

Abstract

System for measuring the level of liquid such as a tide recorder, using hydrostatic pressure and capable of being periodically calibrated by comparison with columns of liquid of the same nature. In Figure 1, we see at 1 a well communicating with the sea whose level is being measured, at 8 and 9, two reference tubes alternately set in communication, as well as the sea, with a differential pressure sensor 5 whose reference face is brought to barometric pressure. When the level falls, the upper reference tube 8 set in communication with the pressure sensor 5 remains full, the pressure measured corresponds to the column of water contained in this tube. The sensor will then measure periodically the levels of the sea then the pressure of the lower reference tube 9. Having two pressure references corresponding to geometrical water heights, independent of density, temperature, barometric pressure, or the drift of the measurement system, it is possible to calibrate it periodically and automatically. This method applies in particular to measuring tides or to limnology.

Description

The invention described below applies inter alia to a tide gauge which aims to measure with millimetric precision the sea level or of a liquid, whatever the agitation of the medium, the barometric pressure variations , temper or salinity
The system is capable of compensating for any drifts in the medium or in the measurement system
The devices currently used to measure the levels, + call on floats slaved to pulleys whose angular displacement is measured, or to pressure sensors measuring the hydrostatic pressure representing the water column surmounting them, or radars, or immersed acoustic sounders looking at the surface.

 All these devices are sensitive to environmental conditions such as barometric pressure, changes in density or temperature or simply the drift of the measurement system itself.

the invention describes a tide gauge with differential pressure sensor alternately weighing the water column which surmounts it and reference water columns, of perfectly known height which serve as reference values for the permanent calibration of the chain of measured
The tide gauge object of the invention is described below, but this description does not constitute a limiting example of other application methods can be used.
The system is installed in a well 115 dug in the ground or constitutes by a masonry along a quay.

it is placed in communication with at sea by a pipe (2).

the bottom of the well (.3) must be firmly attached to the ground; it is this which will serve as a reference for the measurement.

The whole is surmounted by a protective construction (4)
Fixed on the base (3) is installed a pressure sensor; differential (5) one of the faces of which is brought into contact with the barometric pressure by a tube going to the surface (6) the other face is connected to a valve box (7) bringing it in turn into contact with ambient water either with the high reference column (8) or with the low reference column (9).

 The pressure measurements made by the sensor are transmitted by cable (10) to an electronic measuring device (11) which will analyze them, process them, record them and order the work sequences of the system.

 It can advantageously be a data acquisition computer responsible for making the reference measurements, and the level measurements, for correcting them according to the reference measurements, and for dating them, for controlling the solenoid valves and for storing the information on memories, diskettes or magnetic tapes or 4th prepare and manage telemetry messages.

The installation can be supplemented by a filtered water pumping system thus avoiding siltation of the installation.

In this case we see a tube (12) going to the sea, or elsewhere, from where the water is brought by the pump 113) arriving at the settling tank (14) and from there by the tube (15) to the well of measured
In order to avoid the proliferation of fauna and flora, a slight flow of bleach or other equivalent product is regularly poured into the well.
The installation can operate thanks to solar panels
to eliminate the swell effect, the measurement can be extended for a time sufficient to integrate the pressure variations and eliminate the effects
The operations described could be carried out manually
without the invention changing its meaning
Figure II schematically represents the system in order to clearly explain the play of the valves or solenoid valves contained in the valve box (7)
The valve box (7) contains 3 solenoid valves ((17) and (18) controlled by the power station (lt) from the surface.

 These solenoid valves could moreover very easily be replaced by valves controlled by a camshaft driven by a motor or manually.

The level of the water in the well (1) can vary with the rhythm of the tides or changes in level transmitted by the tube to the sea (2)
The pressure sensor (5) is connected to the> reference points (8) and (9) which themselves are connected to the solenoid valves (16) (17) and (18).

 The solenoid valves being all open, the active face of the pressure sensor is in direct communication with the ambient water, on the other hand its other face being in communication thanks to the pipe (6) with atmospheric pressure, it is the column of water which surmounts the sensor which creates the pressure measured by the latter to the exclusion of any effect of atmospheric pressure, this being exerted equally on its 2 faces on the one hand directly by taking air pressure, on the other hand via the surface of the liquid on which it weighs uniformly.

 If by the effect of the tide or an artificial filling the water level exceeds the upper edge of the reference tube (8) that 1 the valves or solenoid valves (16) and (18) are closed and let the water level drop either artificially or because it is a natural variation such as the movement of the tide, the valves (16) and 118) being closed, the reference tube (8) will remain full to the brim and the pressure sensor will measure the pressure caused by the column of water contained in this tube of perfectly known length, whatever the density DU the temperature of the water or the fluid.

 This measurement will serve as reference N 1 for the calibration of the pressure sensor and of the system itself.

 This measurement being made, the solenoid valves (16) (17) and (18) being open, the measurements of the free water level can continue.

 As the level continues to drop as the lower reference tube (9) approaches, the solenoid valve (17) will be closed, the level still falling. The tube (9) will remain full to the brim and the sensor will measure the pressure of the water column of perfectly known height contained in this tube (9).

This second measurement will constitute the reference N "2 '
Now having 2 pressure references corresponding to geometrically known levels, independent of the barometric pressure, temperature or density factors of the fluid to be measured, these 2 references will constitute the 2 calibration points of the pressure sensor curve .

These 7 values being entered in a calculation table, all the pressure measurements of the free water level can be corrected by the calibrated table
It is important here to note that all the measurements being compared to 2 geometric references, the possible drifts of the sensor, the variations of the external physical conditions remain without influence and are periodically corrected
On a practical level it should be noted - that the reference tubes (8) and (9) and the sensor (7) must be perfectly integral with the base (3) and follow any movements therefrom - that the tubes (8 ) and (9) are constructed from a material that shelters them from temperature variations such as invar, quartz or the like.

In summary, the invention relates essentially to a method for periodically calibrating a liquid level measurement system by hydrostatic pressure, by measuring the pressure prevailing in tubes of known length containing the same liquid as that to be measured.
The reference measurements thus obtained serve as a basis for the measurement scale
This periodic calibration of the system by comparison with a purely physical phenomenon makes it possible to eliminate the problems of drift of the pressure sensor, of variation of the environmental conditions such as variations in density of the fluid, its temperature, or variation in the atmospheric pressure.

Claims (11)

REVEHDICATIONS 1 - Method for measuring sea level or surface level  liquids through hydrostatic pressure measurement.  of measurements in relation to the medium.  Characterized by an automatic chain calibration system  the pressure of a water column of geometrically known height.  emerges and they are full to the brim, the sensor then measuring  with the pressure sensor (5) when their upper edge  alternately set up through a set of valves in communication  Consisting of 2 reference tubes (8 and 9) of different sizes, 2 - Device according to claim N 1 using 3 solenoid valves  (16 17 18) to switch the reference columns' 8 and 9) and  the medium at the sensor (5, pressure. 3 - Device according to claim N -i using a series of  valves (16 17 18) driven by an electric motor to switch  the columns (8 and 9, reference and the middle to the sensor  pressure (5). 4 - Device according to claim N 1 using to switch  the reference columns (8 and 9) the medium at the pressure sensor  (5) a series of manually operated valves (16, 17, 18). 5 - Device according to claim N 1 using a sensor  differential pressure (5) of which 1 face is reduced to pressure  atmospheric (6), which eliminates the effects of its variations. 6 - Device according to claim NO 1 using as columns  reference (8 and 9d quartz tubes with dimensions  vary only infinitesimally depending on the temperature. 7 - Device according to claim N 1 using as columns  reference (8 and 9) invar tubes whose dimensions do not  vary only infinitesimally depending on the temperature. 8 - Device according to claim N 1 using as columns  reference (8 and 9) flexible tubes including the upper edge  is firmly attached to a geometrically known base. 9 - Device according to claim N 1 contained in a well provided  at its lower part of a valve and a pump, allowing  at will to isolate it from its environment and to vary its level  in order to perform the calibration maneuvers independently  natural movements. 10 - Device according to claim N 1 provided with a circulation pump  tion ensuring water renewal in order to avoid an increase  salinity due to evaporation. 11 - Device according to claim NO 1 provided with a drip  bleach, intended to prevent the growth of flora and  wildlife in the well.