GB2153616A

GB2153616A - Liquid level measurement

Info

Publication number: GB2153616A
Application number: GB08402586A
Authority: GB
Inventors: Gilles David Pitt; Roger Edward Jones
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1984-02-01
Filing date: 1984-02-01
Publication date: 1985-08-21
Also published as: NO850372L; GB8402586D0; GB2153616B

Abstract

To measure the level of liquid in a container, and also to locate interfaces between different liquids therein, a sensor is placed in the liquid. This has a two-wire transmission line (1) wound helically on a support (2) to which is applied a short sharp pulse. Each interface causes a change in dielectric constant in the vicinity of the line, as a result of which reflection occurs. These reflected pulses appear on a CRT to give indications of the localities of the interfaces. There is also a reflection from the end of the line, which provides further information as to the characteristics of the medium. <IMAGE>

Description

SPECIFICATION Liquid level measurement This invention relates to methods of, and apparatuses for, the measurement of liquid levels and the location of interfces between immiscible liquids.

In U.S. Patent No. 3424002 (Irvin D. Johnson; assigned to Marathon Oil Company), there is described a method of determining the position of interfaces between different materials in which a fast-rise voltage step pulse is applied to one end of a transmission line which passes through the interface, which pulse is partially reflected back by any point at which the impedance of the line changes.

The time interval between the generation of a voltage step pulse and the return of its reflection represents the distance of that reflection point along the transmission line.

With such an arrangement, some difficulties are experienced because of the short distance, and hence short times involved. An object of the invention is therefore to produce a method of and apparatus for measuring liquid levels and locating interfaces, which mitigates or even removes the disadvantages of the known methods.

According to the invention there is provided a method of measuring liquid levels and locating interfaces between different levels, which includes inserting into the liquid or liquids to be measured a plural-wire transmission line wound helically, applying a pulse with a step leading edge and short duration to one end of the line, monitoring the connection to the line for reflected versions of the pulse, each due to a discontinuity such as said surface or a said interface, and giving indications appropriate to each reflection from the surface of the liquid and each interface between different liquids.

Apparatus embodying the invention will now be described with reference to the accompanying drawing, in which Figure 1 is a simplified representation of that apparatus, while Figure2 is a typical oscilloscope trace obtained with the apparatus of Figure 1.

Figure 1 shows the arrangement of a parallel pair transmission line sensor for detecting liquid level and the position of interfaces between immiscible liquids. This line 1 is helically wound around a support member 2, and the wires of the line are insulated from each other electrically.

A pulse (typically 5 ns wide or narrower) from a pulse generator 3 is launched into the transmission line via termination 4, and propagates down the line at a velocity determined by the dielectric constant of the fluid in the vicinity of the transmission line. At a discontinuity of dielectric constant, such as the interface 5 between air and oil, or the interface 6 between oil and water, a portion of the incident pulse is reflected, and appears on the oscillopscope 7.

The time interval between despatch of the pulse and reception of the reflected pulse is a measure of the level of liquid at the point at which the reflection occurred, i.e. at the upper surface of the liquid, at each inter-liquid interface, and also at the end of the line. The line is either terminated with a resistor or other impedance, or left unterminated dependent on circumstances.

Additional information is obtained from the time taken for the pulse reflected from the end of the line to return. This latter time shifts according to the total transit time down the line, and thus varies in accordance with the changes of dielectric constant along the sensor.

The difficulty with the known system due to the iack of spatial resolution due to the short time intervals are overcome by the coiling ofthetrans- mission line into a helical form, which improves the time separation of close spatial interfaces, and in fact improves the resolution by a factor of 10. Also fast electronics using emitter coupled logic are used for the signal processing.

In the typical oscilloscope trace shown in Figure 2, the outgoing pulse is shown at 10, and a reflection due to the connection to the sensor is shown at 11.

The oil-air interface produces the reflected pulse 12, the oil-water interface produces the reflected pulse 13, and the end of the line produces the pulse 14.

1. A method of measuring liquid levels and locating interfaces between different levels, which includes inserting into the liquid or liquids to be measured a plural-wire transmission line wound helically, applying a pulse with a steep leading edge and short duration to one end of the line, monitoring the connection to the line for reflected versions of the pulse, each due to a discontinuity such as said surface or a said interface, and giving indications appropriate to each reflection from the surface of the liquid and each interface between different liquids.

2. A method as claimed in claim 1, and in which the time at which the pulse is reflected from the end of the transmission line is determined, which termination provides information as to the depth of the liquid and the characteristics thereof.

3. A method of measuring liquid levels and locating interfaces between different liquids, substantially as described with reference to the accompanying drawing.

4. Apparatus for implementing the method of claim 1, 2 or 3.

New claims or amendments to claims filed on 24 July 1984 New or amended claims as follows: 5. A method of measuring liquid levels and of locating interfaces between different levels, which includes inserting into the liquid or liquids in respect of which measurement is to be effected a two-wire insulated transmission line wound helically on a former, such that the insulated line is in physical contact with the liquid or liquids, applying a pulse with a steep leading edge and short duration to one end of the line, so that the pulse propagates down the line to its end and is reflected therefrom, the velocity of said progagation being dependent upon the dielectric constant of the air or the fluid in contact with the line, monitoring the connection to the line

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Liquid level measurement This invention relates to methods of, and apparatuses for, the measurement of liquid levels and the location of interfces between immiscible liquids. In U.S. Patent No. 3424002 (Irvin D. Johnson; assigned to Marathon Oil Company), there is described a method of determining the position of interfaces between different materials in which a fast-rise voltage step pulse is applied to one end of a transmission line which passes through the interface, which pulse is partially reflected back by any point at which the impedance of the line changes. The time interval between the generation of a voltage step pulse and the return of its reflection represents the distance of that reflection point along the transmission line. With such an arrangement, some difficulties are experienced because of the short distance, and hence short times involved. An object of the invention is therefore to produce a method of and apparatus for measuring liquid levels and locating interfaces, which mitigates or even removes the disadvantages of the known methods. According to the invention there is provided a method of measuring liquid levels and locating interfaces between different levels, which includes inserting into the liquid or liquids to be measured a plural-wire transmission line wound helically, applying a pulse with a step leading edge and short duration to one end of the line, monitoring the connection to the line for reflected versions of the pulse, each due to a discontinuity such as said surface or a said interface, and giving indications appropriate to each reflection from the surface of the liquid and each interface between different liquids. Apparatus embodying the invention will now be described with reference to the accompanying drawing, in which Figure 1 is a simplified representation of that apparatus, while Figure2 is a typical oscilloscope trace obtained with the apparatus of Figure 1. Figure 1 shows the arrangement of a parallel pair transmission line sensor for detecting liquid level and the position of interfaces between immiscible liquids. This line 1 is helically wound around a support member 2, and the wires of the line are insulated from each other electrically. A pulse (typically 5 ns wide or narrower) from a pulse generator 3 is launched into the transmission line via termination 4, and propagates down the line at a velocity determined by the dielectric constant of the fluid in the vicinity of the transmission line. At a discontinuity of dielectric constant, such as the interface 5 between air and oil, or the interface 6 between oil and water, a portion of the incident pulse is reflected, and appears on the oscillopscope 7. The time interval between despatch of the pulse and reception of the reflected pulse is a measure of the level of liquid at the point at which the reflection occurred, i.e. at the upper surface of the liquid, at each inter-liquid interface, and also at the end of the line. The line is either terminated with a resistor or other impedance, or left unterminated dependent on circumstances. Additional information is obtained from the time taken for the pulse reflected from the end of the line to return. This latter time shifts according to the total transit time down the line, and thus varies in accordance with the changes of dielectric constant along the sensor. The difficulty with the known system due to the iack of spatial resolution due to the short time intervals are overcome by the coiling ofthetrans- mission line into a helical form, which improves the time separation of close spatial interfaces, and in fact improves the resolution by a factor of 10. Also fast electronics using emitter coupled logic are used for the signal processing. In the typical oscilloscope trace shown in Figure 2, the outgoing pulse is shown at 10, and a reflection due to the connection to the sensor is shown at 11. The oil-air interface produces the reflected pulse 12, the oil-water interface produces the reflected pulse 13, and the end of the line produces the pulse 14. CLAIMS

4. Apparatus for implementing the method of claim 1, 2 or 3.

New claims or amendments to claims filed on 24 July 1984 New or amended claims as follows:

5. A method of measuring liquid levels and of locating interfaces between different levels, which includes inserting into the liquid or liquids in respect of which measurement is to be effected a two-wire insulated transmission line wound helically on a former, such that the insulated line is in physical contact with the liquid or liquids, applying a pulse with a steep leading edge and short duration to one end of the line, so that the pulse propagates down the line to its end and is reflected therefrom, the velocity of said progagation being dependent upon the dielectric constant of the air or the fluid in contact with the line, monitoring the connection to the line for reflected versions of the pulse, each due to a discontinuity such as the interface between the air and the liquid, and the interfaces between different liquids and the other end of the line, and giving indications appropriate to each said reflection from a said interface or said other end of the line.

6. Apparatus for measuring liquid levels and for locating interfaces between different levels, which includes a two-wire insulated transmission line wound helically on a former, which when in use is inserted into the liquid or liquids in respect of which measurement is to be effected, such that the insulated line is in physical contact with the liquid or liquids, a connection via which a pulse with a steep leading edge and short duration is applied to one end of the line, so that the pulse propagates down the line to its end and is reflected therefrom, the velocity of said progagation being dependent upon the dielectric constant of the air or the fluid in contact with the line, means for monitoring the connection to the line for reflected versions of the pulse, each due to a discontinuity such as the interface between the air and the liquid, and the interfaces between different liquids and the other end of the line, and means for giving indications appropriate to each said reflection from a said interface or said other end of the line.