BE1007039A3 - System and method for measuring the level of moisture in a sample of aliquid substance - Google Patents

Abstract

System and method for measuring the level of moisture in a sample of aliquid substance, notably crude oil, said system including a measurement cellmade of a dielectric material and having a cavity set up for receiving thesample. The cell can be connected in reference and measurement moderespectively in which an incident microwave signal passes through thedielectric material and the cavity respectively and the dielectric material.The connection is made using deflection methods for deflecting the microwavesignal inside the cell. The degree of moisture is determined on the basis ofthe result obtained when the cell is connected in the reference andmeasurement modes.

Description

"Device and method for measuring the humidity of a sample of a liquid substance" The invention relates to a device for measuring the humidity of a sample of a liquid substance, in particular crude oil, said device comprising a measurement cell which comprises connection means arranged to connect said cell in a reference mode, respectively a measurement mode, a microwave signal generator arranged to produce a first microwave signal and transmit said first microwave signal to said cell, a receiver arranged to receive a second, respectively a third, microwave signal produced from the transmission of said first microwave signal through said cell when plugged into said cell reference mode, respectively said measurement mode, said receiver being connected to a measurement value generator arranged to produce, at from said second and third microwave signal, a measurement value indicating said degree of humidity. The invention also relates to a method for measuring such a degree of humidity.

Such a device and such a method are known from Russian author's certificate No. 1015287. In the known device, the sample containing the liquid substance of which the degree of humidity is to be measured is moved in and out of a beam produced by the first microwave signal. When the sample is outside the beam, the device is connected to the reference mode in order to measure a reference signal or an unattenuated signal. When the sample is placed in the beam, part of the energy of the microwave signal is absorbed by the moisture in the sample. The amount of energy absorbed will depend on the degree of humidity contained in the sample,. The degree of humidity in the sample is thus determined from the difference between the signal measured in the reference mode and that measured in the measurement mode. The received signal is supplied to a measured value generator which determines the measured value and displays it.

A disadvantage of the known device and method is that they are not applicable for measurements of the degree of humidity of a substance which circulates continuously, for example through a pipeline. This is because a reference sample must be introduced into the beam of the microwave signal in order to produce the second microwave signal. Therefore, the direct current of the liquid substance must be interrupted when the device is connected in the reference mode. In the example of crude oil flowing in the pipeline, such an interruption in the flow of oil should be avoided.

The object of the invention is to provide a device and a method for measuring the humidity of a sample of a liquid substance which makes it possible to carry out this measurement without having to interrupt the direct current of the liquid substance.

A device according to the invention is characterized in that said cell is constructed of a dielectric material and comprises a cavity arranged to introduce said sample therein, said connection means being formed by microwave signal deflection means mounted in the dielectric material, said deflection means being arranged to orient said first microwave signal in a reference channel which extends through said dielectric material respectively a measurement channel which extends through said dielectric material and said cavity when 'they are connected in a first, respectively a second, position. The use of a cell made of dielectric material makes it possible to substantially reduce the energy losses of the microwave signal. In addition, this dielectric material makes it possible to mount deflection means inside the cell thus allowing deflection of the microwave signal in the cell. Because the cell has a cavity, the sample can be introduced into it at any time, which therefore makes it possible to carry out the measurement in a direct current of a liquid substance passing through this cavity. Due to the fact that the measurement channel extends through the dielectric material and the cavity and that the reference channel only extends through the dielectric material, the cell can be connected from the measurement mode to the reference mode without having to interrupt the flow of liquid substance, which therefore makes it possible to carry out a measurement in a current which circulates continuously.

A first preferred embodiment of a device according to the invention is characterized in that said deflection means are formed by a set of magnetic plates, each in combination with a grid, said magnetic plate being disposed in front of said grid relative to an incident signal, said magnetic plate and said grid being electrically polarizable. The use of magnetic plates and grids is compatible with the dielectric material of the cell and makes it possible to orient the microwave signal inside the cell.

A second preferred embodiment of a device according to the invention is characterized in that said deflection means and said microwave signal generator are connected to a control unit arranged to produce first, respectively second, pulses control means for controlling said microwave signal generator, respectively said deflection means, said first and second control pulses being synchronized with each other. Synchronization facilitates the control and operation of the measured value generator.

Preferably, an attenuator and an impedance matching element are disposed between said cell and said microwave signal generator. Losses due to transitions between the cell and the transmitter and the receiver are thus reduced.

The invention will now be described in detail with reference to the drawings in which: FIG. 1 illustrates an experimental curve of the measurement error SW in the degree of humidity measured as a function of the wavelength of the transmitted signal; Figure 2 shows a schematic view of an example of a device according to the present invention; Figure 3 illustrates how the device according to the present invention can be mounted on a pipeline; Figure 4 shows a series of control signals to control the operation of the device.

In the drawings, the same reference has been assigned to the same element or to an analogous element.

The experimental curve illustrated in Figure 1, which shows the measurement error SW (expressed in% of volume) in the 1st degree of humidity of the crude oil measured as a function of the wavelength (expressed in mm) of the signal transmitted, shows that there is a minimum in this error. This minimum is in a wave range between 1.5 and 2.5 mm. This curve was established experimentally and is the result of various measurements made on different varieties of crude oil. This curve shows that in order to keep the measurement error sufficiently low, it is necessary to use a signal whose wavelength λ is between 1.5 and 2.5 mm, that is to say say a microwave signal.

Figure 2 shows an example of a device according to the invention for measuring the humidity of a sample of a liquid substance, in particular crude oil. The device 1 comprises a power supply and synchronization unit 2 connected to a microwave signal generator 3 provided with a transmission antenna 4 having the shape of a horn. The device further comprises a receiver 6 also provided with an antenna 5 having the shape of a horn. The receiver is connected to a measurement value generator 7 provided with a display unit 8 arranged to display the value of the measured degree of humidity. The measured value generator 7 is also connected to the power supply and synchronization unit for reasons which will be described below.

The device also comprises a measuring cell 9 made of a dielectric material having a dielectric constant e situated in a range: 9 <e <25. The dimension 1, d of the cell is chosen so that all of the components of the cell are located in a near field of the transmission antenna, that is to say:

in which λ is the wavelength of the microwave signal used and produced by the generator 3, L the length of the path traveled by the beam through the measurement channel and b the dimension of the opening of the radiation field of the antenna. The dielectric material is either homogeneous or non-homogeneous.

The measuring cell 9 has a cavity 10 which extends through the cell and is provided to receive the sample to be measured. The cavity is located between two dielectric plates 11 and 12, formed for example by X / 4 plates. The plates are used for an adaptation of the impedance and therefore make it possible to reduce the losses of the signal due to reflections during the transmission between the dielectric material of the cell and the sample.

Between the transmitting antenna 4, respectively the receiving antenna 5, and the dielectric material of the cell 9 is mounted an element 13, respectively 15, allowing adaptation of the impedance. The impedance matching element prevents impedance losses between the antenna and the cell. A dielectric plate 14 made of a material making it possible to absorb the microwave signal is also disposed between the impedance matching element 13 and the cell 9. The plate 14 is in contact with the cell and the the impedance matching element 13 and allows a reduction of the microwave signal for normal operation of the receiver 6.

Deflection means are mounted in the measurement cell 9. These deflection means are arranged to orient the incident microwave signal inside the measurement cell. The deflection means are formed by a set of magnetic plates with metal grids. A first set is formed by the metal grid. 17 and the magnetic plate 16 placed in the direct vicinity of the transmission antenna 4. The magnetic plate is arranged in front of the grid with respect to the incident direction of the signal, that is to say that the incident signal first reaches the magnetic plate and then the grid. The metal grid 17 forms an angle of approximately 45 ° relative to the magnetic plate 16 which is arranged substantially in parallel with the exit surface of the antenna horn 4. The inclination of the grid 17 causes a deflection of the microwave signal as a function of the current applied to the magnetic plate 16, as will be described in detail below.

A second set, formed by the metal grid 19 and the magnetic plate 18, is arranged to the left of the transmitter. A third set, formed by the metal grid 21 and the magnetic plate 20, is placed behind the cavity 10. In the second and the third set, the grid and the magnetic plate are placed substantially parallel with respect to the other. A fourth set, formed by the magnetic plate 22 and the metal grid 23, is placed in the vicinity of the receiver 5. The metal grid 23 forms an angle of approximately 45 ° in order to direct the signal towards the receiving antenna 5. Preferably at least part of the dielectric material located behind the grids 19, 21 and 23 is made of an absorbent material thus making it possible to eliminate parasitic reflections between the various components of the measurement cell.

Each of the games is connected by means of wires 24 to the power and synchronization unit 2. For the sake of clarity, the wiring inside the cell is not illustrated.

The operation of the device and of the various steps of the measurement method will now be described in more detail. Figure 4 shows a series of control signals to control the operation of the device. The signal illustrated in Figure 4 (b) is produced by the power supply and synchronization unit 2 and supplied via lines 24 by means of deflection. At instant tlf after initialization of the device, a first control signal is produced, for example a signal having a positive level of 5 volts to connect the cell in the reference mode. The first control signal maintains this high level during a period Δ Ti = t3 - tj of for example one second. During this period Δ T ,, the measurement cell is maintained in the reference mode. When the cell is connected in the reference mode, the current applied to the magnetic plates 16, 18, 20 and 22 will cause the first incident microwave signal, illustrated under (c) in Figure 4, to be oriented according to a reference channel as shown in Figure 2 by the dotted lines. The first microwave signal produced at time t2 during the period Δ T, is polarized according to a first plane of polarization in order to be compatible with the first control signal applied to the magnetic plates and will cause the signal to microwave injected into the dielectric material will be deflected along the reference channel.

When the measuring cell is connected in the reference mode, the first microwave signal is deflected by the first set (16, 17) towards the second set (18, 19). The grid 19 reflects the signal to the magnetic plate 22 and the grid 23. In the reference mode, the signal remains inside the dielectric material and does not cross the sample located in the cavity 10.

The receiver 5 now receives a second microwave signal (U [), illustrated in (d) in Figure 4, when the measurement cell is connected in the reference mode. The power of the second signal Uj represents the reference power (Pr) of the radiation. Because this second microwave signal crosses only the dielectric material, the losses are relatively low and are strictly determined by the dielectric material of the cell and the reflection up to the first, second and fourth sets of deflection means.

At an instant t3, the falling level of the first control signal will cause the production of a second control signal, illustrated under (e) in Figure 4. This second signal is produced by the power supply and synchronization unit. This control signal is supplied to the measurement value generator 7. Under the control of this second control signal, the generator receives the value Pr of the second microwave signal and temporarily stores this value. Since the second control signal is activated by the falling level of the first control signal, the two signals are synchronized with each other, which allows the generator 7 to be activated at a time when the signal has been received by the receiver 5.

At an instant t3, the polarity of the first control signal changes. In the present example, the signal changes from a positive level to a negative level of, for example, -5 volts. The polarity of the first microwave signal (Figure 4 (c)) also changes during the second period ΔΤ2 = t5 - t3. During this second period ΔΤ2 the polarity of the first control signal and of the first microwave signal are opposite with respect to those during the period ΔΤ ^

This opposite polarity will now cause the measurement cell to plug into the measurement mode and direct the incident microwave signal into the measurement channel. The measurement channel is indicated by the solid lines in Figure 2 and extends through the dielectric material and the cavity 10 into which the sample is introduced. The grid 17 will now cause the incident microwave signal to be directed through the cavity and cross the sample comprising the liquid substance passing through said cavity. The microwave signal is reflected by the magnetic plate 20 and the grid 21 and crosses the sample again before reaching the grid 17. The grid 17 then directs the signal to the magnetic plate 22 and the grid 23 in order to direct the signal to the receiver 5.

When the measuring cell is connected in the measuring mode, a third microwave signal (U2) is produced, which is obtained by letting the first incident microwave signal cross the dielectric material of the cell and the liquid substance. of the sample. The power (Pm) of the third microwave signal will be less than the power (Pr) of the second microwave signal since part of the energy of the incident microwave signal has been absorbed by the humidity present. in the sample to be measured. The more moisture present in this sample, the more energy will have been absorbed and the weaker will be the third signal.

The rising level of the first control signal at time t5 will cause the production of another control signal as illustrated in Figure 4 (e). This other control signal will force the generator 7 to read the signal received by the detector 6. Now the measurement value generator knows the values Pr and Pm and can determine from these values the degree W of sample moisture measured. To this end, the generator applies the following calculation:

Δα = 10 log (Pr / PJ

in which A and B are coefficients representing a mean value of the coefficients of zero expansion and one of the function Δα (W) in an exponential series following w. The humidity level is displayed on the display unit 8.

Since the measurement of the reference power Pr and the measurement of the measurement power Pm are carried out consecutively using the same measurement cell, the same transmitter and the same receiver, fluctuations in time and in temperature will not affect these results. The measurement cycle (ATj + ΔΤ2) is short enough that time cannot negatively affect the measurement values.

The use of a measuring cell made of a dielectric material significantly reduces the parasitic effects due to reflections between the receiving and transmitting antenna and the cell. The measurement error can also be reduced by varying the frequency of the microwave signal, so that residual interference from spurious beams is leveled.

The incident signal passes twice through the sample and is therefore more sensitive to humidity compared to a device where the incident beam only passes once through the sample.

The cavity in the measuring cell makes it possible to mount the device for example on a pipeline as illustrated in Figure 3. In this way it is possible to measure the degree of humidity in a direct current of a liquid substance, such as for example crude oil.

Claims (5)

1. Device for measuring the humidity of a sample of a liquid substance, in particular crude oil, said device comprising a measurement cell which comprises connection means arranged to connect said cell in a reference mode, respectively a measurement mode, a microwave signal generator arranged to produce a first microwave signal and transmit said first microwave signal to said cell, a receiver arranged to receive a second, respectively a third, signal microwave produced from the transmission of said first microwave signal through said cell when it is connected in said reference mode, respectively said measurement mode, said receiver being connected to a measurement value generator arranged to produce, from said second and third microwave signal, a measurement value indicating said humidity, characterized in that said cell is constructed of a dielectric material and comprises a cavity arranged to introduce said sample therein, said connection means being formed by microwave signal deflection means mounted in the dielectric material, said deflection means being arranged to orient said first microwave signal in a reference channel which extends through said dielectric material respectively a measurement channel which extends to. through said dielectric material and said cavity when plugged into a first, respectively a second, position. 2. Device according to claim 1, characterized in that said deflection means are closed by a set of magnetic plates each in combination with a grid, said magnetic plate being disposed in front of said grid with respect to an incident signal, said magnetic plate and said grid being electrically polarizable. 3. Device according to claim 2, characterized in that said deflection means and said microwave signal generator are connected to a control unit arranged to produce first, respectively second, control pulses to control said generator. microwave signal respectively said deflection means, said first and second control pulses being synchronized with each other. 4. Device according to one of claims 1 to 3, characterized in that an attenuator and an impedance matching element are arranged between said cell and said microwave signal generator. 5. Method for measuring the humidity of a sample of a liquid substance, in particular crude oil, by which said sample is introduced into a measurement cell, irradiated by a first microwave signal in order to produce a third microwave signal which is received by a receiver, a second microwave signal being produced and supplied to said receiver by transmission of said first signal through a reference channel in said cell, a measurement value being determined from of the second and third signal, characterized in that said sample is introduced into a dielectric medium forming said cell, said second respectively third signal being produced by deflection of said first signal inside said cell.