GB2046912A

GB2046912A - A liquid level detector

Info

Publication number: GB2046912A
Application number: GB7916073A
Authority: GB
Original assignee: Edworthy K J; SKILLING J A CHILDS M A BROWN
Current assignee: Edworthy K J; SKILLING J A CHILDS M A BROWN
Priority date: 1979-05-09
Filing date: 1979-05-09
Publication date: 1980-11-19
Also published as: GB2046912B

Abstract

A detector for detecting the level of a liquid/air interface below a given reference level, and for detecting any oil which may be present thereat. The detector comprises a reel 12 on which is wound a graduated tape 14 carrying graduations 15, the tape having conductors embedded therein for interconnecting a probe assembly 16 attached to the free end of the tape and an electronic circuit mounted within the core of the reel 12. The probe assembly 16 includes a float switch 20 and electrodes 19, the circuit serving to detect operation of the float switch by an air/liquid interface, and to detect a drop in impedance between the electrodes. The circuit provides outputs which illuminate light-omitting diodes 22, dependent upon whether the probe assembly contacts a conducting fluid (impure water) or a non-conducting fluid (oil). <IMAGE>

Description

SPECIFICATION A liquid level detector This invention relates to a liquid level detector, and in particular to a detector able to discriminate between an oil level and a water level.

In the water-supply industry, it is frequently necessary to determine the position of the water surface in a bore hole or in a well. In the case of a bore hole, this often is only about 100 mm diameter, and the usual procedure is to lower a suitable probe down the hole until the water surface is contacted and because of the relatively small diameter of the hole, it is very difficult to see actually when the surface is reached.

It is furthermore of interest to know whether there is any oil on the surface of water in a well or bore hole, and if so, how much. Though the known probes which can be lowered into the bore holes may indicate the liquid level, they do not give any accurate indication of the presence of oil. Since even a relatively thin layer of oil on water in a well can sufficiently contaminate the water to require some corrective action-such as determining the source of the oil and preventing further escapes thereof-it is of advantage to be able to determine the presence of oil layers of as small as 1 cm thick.

It is a principal aim of this invention to provide a liquid level detector which can determine the level of liquid in a bore hole, well or the like and disciminate between oil or other non-conductive liquid and water.

According to this invention, there is provided a liquid level detector comprising a probe assembly for lowering into liquid which probe includes an electrical float switch operable by a liquid surface and a pair of electrodes electrically insulated from one another, the detector further comprising an electronic circuit responsive to operation of the float switch to produce a first output and responsive to a fall in electrical resistance between the electrodes to below a threshold level to produce a second output, a flexible tension element including conductors interconnecting the electronic circuit and the float switch and electrodes of the probe assembly, and means determining the length of flexible tension element between the probe assembly and a reference point.

It will be appreciated that in this invention, the float switch will be operated in response to the probe assembly being lowered to a liquid/air interface, so that the electronic circuit gives its first output. Because water is a relatively good electrical conductor as compared with oil, if the contacted liquid is water, the electronic circuit will give its second output as well, but if the liquid is oil, only the first output is given. In this case, the probe assembly can be lowered further into the liquid, until the second output is given, and the amount by which the probe is lowered after the first output is obtained in order to get the second output is indicative of the thickness of the oil layer.

The flexible tension element must be sufficiently strong to support the probe assembly, and the length thereof must be sufficient for the intended application of the detector: a typical bore hole detector would require a tension element of about 50 m long. Conveniently, the tension element is wound on a drum or reel and can be paid out as required to lower the probe; in this case the length determining means can be associated with the reel, to give an indication of the amount paid out. It is however preferred for the length determining means to be associated directly with the flexible tension element itself, for instance by graduations marked on the element at regular intervals therealong. Thus, the tension element may be in the form of a tape having the required conductors embedded therein and graduations marked thereon at regular intervals.Such a tape may be wound on a suitable reel for storage purposes, and then unwound as required.

The first and second outputs from the electronic circuit are preferably visible signals, given for instance by suitable arrays of lightemitting diodes. Instead of, or in addition to, the visible outputs, audible alarms of two distinct characters may be employed, such as two separate audible notes. In the case of visible outputs, when these are to be activated they may be flashed on and off to attract attention.

The electronic circuit conveniently employs semiconductor technology and has a first part responsive to operation of the float switch and a second part responsive to resistance between the electrodes of the probe. The first part conveniently includes a transistor switch operated by closing of the float switch on contacting a liquid surface, and a gating circuit arranged to cause a display to flash on and off when the transistor switch is operated.

The second part conveniently is arranged to apply an A.C. waveform across the electrodes of the probe assembly and then to trigger a transistor switch if the impedance falls below a threshold level: by employing A.C. polarisation at the electrodes is eliminated. A gating circuit preferably is employed between the transistor switch and a display, to cause the display to flash in the same manner as the display controlled by operation of the float switch.

In the case in which the tension member is wound on a reel for storage, the electronic circuit and its power source are preferably built into the core of the reel, to make a selfcontained unit. The displays for the first and second outputs can then be incorporated in an end face of the reel, so as to be easily visible.

The probe assembly conveniently has a guard to protect the float switch and to prevent the operation thereof as the probe is being lowered down a hole, by inadvertent contact with the wall of the hole. The float switch preferably is of the normally-open type, which is closed on being operated by a liquid/air interface, and the electrodes of the probe assembly preferably are in the form of stainless steel pins. The relative positions of the float switch and the electrodes should be such that as the probe is lowered into a liquid, at the moment the float switch is operated, the electrodes contact the liquid surface.

By way of example only, one specific embodiment of this invention will now be described, reference being made to the accompanying drawings, in which: Figure 1 is a perspective view of a liquid level detector constructed in accordance with this invention; Figure 2 is a side view of the probe assembly used in the detector of Fig. 1, but with one guard removed for clarity; Figure 3 is a plan view of the probe assembly of Fig. 2; and Figure 4 is a block diagram of the electronic circuit used in the liquid level detector of Fig.

1.

Referring initially to Figs. 1 to 3 of the drawings, the liquid level detector comprises a frame 10 which has a pair of feet 11 and rotatably supports a reel 1 2 having a winding knob 13. Wound on the reel is a flexible fibreglass reinforced plastics material tape 1 4 having three conductors (not shown) embedded therein, the conductors being insulated from one another. The tape 14 carries graduations 15, for example at every centimetre with every metre also being identified by appropriate markings. The tape typically is of 50 m length.

Attached to the free end of the tape 14 is a probe assembly 16, comprising a rigid plastics termination tube 1 7 mounted on box 18 having a pair of guard flanges 1 9 extending parallel to one another from one face. Between the flanges 1 9 are mounted a float switch 20 and a pair of stainless steel electrodes 21, the switch 20 being of the normally-open type and the electrodes being electrically insulated from one another. The conductors within the tape 14 are appropriately connected within the box 1 8 to the electrodes and the float switch, the box then being filled with a potting compound to ensure reliable connections are made, sealed hermetically from the environment.The box 1 8 and the guard flanges 1 9 are preferably made from a durable plastics material, such as polyvinylchloride.

Within the core of the reel 1 2 there is arranged an electronic circuit (not shown) connected to the conductors of the tape 14, together with a power source for the circuit.

The circuit drives a display made up of twelve light-emitting diodes 22 arranged generally in the shape of a letter W; the six left-hand diodes can be illuminated separately from the other six so that the display can selectively show an approximation of the letter L (for 'level') or the letter W (for 'water'). A batterystate indicator 23 is also provided, which is illuminated if the power source has sufficient energy to drive the circuit, and an on/off switch 24.

The electronic circuit will now be described with reference to Fig. 4. The probe assembly 1 6 comprising the float switch 20 and the electrodes 21 are connected by three conductors disposed within the tape 14 to the circuit, one of the conductors being a common return. The float switch 20 is arranged to close on contacting liquid, and thus to connect line 25 to the supply common from a battery 26.

This is detected by a detector circuit 27 including a transistor switch to give a signal on line 28 to a first gate-circuit 29 and a second gate circuit 30. An oscillator 31 feeds a 5 Hz signal to both gate circuits 29 and 30, so that only when both the oscillator signal and the signal from the detector circuit 27 are present, can the display device 32 be energised. This device 32 comprises the first six light-emitting diodes 22, so as to show the letter L when energised.

An oil/water discriminator circuit 33 is connected to line 34 leading to one electrode of the pair thereof, the other electrode being connected to the supply common. The discriminator circuit impresses across the two electrodes an A.C. waveform of about 1 kHz, and monitors the impedance offered to that impressed waveform; when the impedance falls below a pre-set threshold, the discriminator triggers a transistor switch to give a signal on line 35 leading to the second circuit 30.

Provided a signal already is present on line 28 from the liquid detector circuit 27, a display device 36 will be energised when a signal from the oscillator 31 also is present. The display device 36 comprises the second six light-emitting diodes 22, so that when both displays simultaneously are energised, the letter W will be shown.

The state of the battery 26 is monitored by a circuit 37, which drives the indicator 23 (Fig. 1). This indicator is energised when the switch 24 is on and sufficient battery energy is available; at all other times the indicator remains extinguished.

In use, the electronic circuit is turned on, and the probe assembly 1 6 is lowered down a bore hole or well until the float switch is operated on contacting the air/liquid interface. This causes the letter L of the display to be illuminated, but flashing on and off at 5 Hz. The relative positions of the float switch 20 and pair of electrodes 21 are such that at the point at which the float switch closes, the electrodes just contact the liquid. Thus, should the contacted liquid be water, the discriminator circuit 33 detects the relatively low resistance offered by water and causes the other half of the display to be energised, thus showing a letter W, flashing on and off at 5 Hz. The graduations marked on the tape can be read off at the mouth of the bore hole or well, accurately to show the level of the liquid surface relative to the mouth.

If oil is present on the water, only the letter L is illuminated, but the probe can be lowered further, until the letter W is illuminated, on reaching water. By again reading off the graduations on the tape, an accurate assessment of the thickness of the oil layer on the water can be obtained.

Claims

1. A liquid level detector comprising a probe assembly for lowering into liquid which probe includes an electrical float switch operable by a liquid surface and a pair of electrodes electrically insulated from one another, the detector further comprising an electronic circuit responsive to operation of the float switch to produce a first output and responsive to a fall in electrical resistance between the electrodes to below a threshold level to produce a second output, a flexible tension element including conductors interconnecting the electronic circuit and the float switch and electrodes of the probe assembly, and means determining the length of flexible tension element between the probe assembly and a reference point.

2. A liquid level detector as claimed in claim 1, wherein the flexible tension element is wound on a drum or reel for paying out as required to lower the probe under gravity.

3. A liquid level detector as claimed in claim 1 or claim 2, wherein the length determining means comprise graduations marked on the flexible tension element at regular intervals therealong.

4. A liquid level detector as claimed in claim 3, wherein the flexible tension element is in the form of a tape having the required conductors embedded therein and graduations marked along the surface thereof at regular intervals.

5. A liquid level detector as claimed in any of the preceding claims, wherein the first and second outputs from the electronic circuit cause visible signals to be energised.

6. A liquid level detector as claimed in any of the preceding claims, wherein the first and second outputs from the electronic circuit cause audible alarms of two distinct characters to be energised.

7. A liquid level detector as claimed in any of the preceding claims, wherein the electronic circuit has a first part responsive to operation of the float switch and a second part responsive to resistance between the electrodes of the probe.

8. A liquid level detector as claimed in claim 7, wherein the first part includes a transistor switch operated by closing of the float switch on contacting a liquid surface, and a gating circuit arranged to cause a visible display means to flash on and off when the transistor switch is operated.

9. A liquid level detector as claimed in claim 7 or claim 8, wherein the second part is arranged to apply an A.C. waveform across the electrodes of the probe assembly and then to trigger a transistor switch if the impedance falls below a threshold level.

10. A liquid level detector as claimed in claim 9, wherein a gating circuit is employed between the transistor switch of the second part and a visible display means, to cause the display to flash on and off when the second part transistor switch is operated.

11. A liquid level detector as claimed in claim 2 or any claim appendant thereto, wherein the electronic circuit and a power source therefor are built into a central core of the reel, whereby the liquid level alarm is a self-contained unit.

1 2. A liquid level detector as claimed in claim 11, wherein alarm means in the form of displays for the first and second outputs are incorporated in an end face of the reel.

1 3. A liquid level detector as claimed in any of the preceding claims, wherein the probe assembly has a guard arranged to protect the float switch and to prevent the operation thereof other than by an air/liquid interface.

14. A liquid level detector as claimed in any of the preceding claims, wherein the float switch is of the normally-open type, the contacts of which are closed upon the switch being operated by a liquid/air interface.

1 5. A liquid level detector as claimed in any of the preceding claims, wherein the electrodes of the probe assembly are in the form of stainless steel pins.

1 6. A liquid level detector substantially as hereinbefore described with reference to and as illustrated in the accompanying drwings.