CA1130441A - Liquid storage tank contents gauge - Google Patents
Liquid storage tank contents gaugeInfo
- Publication number
- CA1130441A CA1130441A CA295,662A CA295662A CA1130441A CA 1130441 A CA1130441 A CA 1130441A CA 295662 A CA295662 A CA 295662A CA 1130441 A CA1130441 A CA 1130441A
- Authority
- CA
- Canada
- Prior art keywords
- liquid
- tank
- signal
- transducer
- volume
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
- G01F23/296—Acoustic waves
- G01F23/2962—Measuring transit time of reflected waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/26—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
- G01F23/263—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Thermal Sciences (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Acoustics & Sound (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
- Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A liquid storage tank contents gauge comprises means providing an electrical signal corresponding to the vertical height of the liquid in a tank in the form of an ultrasonic transducer positioned at the base of the tank and emitting a pulse of accoustic energy vertically upwards and which detects the pulse when reflected from the liquid/air interface within the tank and including timing means provided to time the interval between the emission of the pulse and the detection of the reflected pulse electronic means for deriving, the volume liquid correspoding to the vertical height, and an output means for providing a visual output of thin volume.
A liquid storage tank contents gauge comprises means providing an electrical signal corresponding to the vertical height of the liquid in a tank in the form of an ultrasonic transducer positioned at the base of the tank and emitting a pulse of accoustic energy vertically upwards and which detects the pulse when reflected from the liquid/air interface within the tank and including timing means provided to time the interval between the emission of the pulse and the detection of the reflected pulse electronic means for deriving, the volume liquid correspoding to the vertical height, and an output means for providing a visual output of thin volume.
Description
11304 ~
~he present invention relates tG a conten-ts gauge for use with a li~uicl s-torage tank, Ic~r e~a~le a petroleu~
storage tark. More s~ecifically the gauge accordi~r to the present invention measures and gives an indication of the volume o liquid y:cesent in the tcL~ll{ and can be readily
~he present invention relates tG a conten-ts gauge for use with a li~uicl s-torage tank, Ic~r e~a~le a petroleu~
storage tark. More s~ecifically the gauge accordi~r to the present invention measures and gives an indication of the volume o liquid y:cesent in the tcL~ll{ and can be readily
2,dapted for use ~ th taL~ks of any shape.
Enown designs o-f gauge can only be used ~,lith tanks of one parti~u~a~ shaL~e and size and re-calibration for ta-nks of other shapes and sizes is difficuLt.
According to the present invention there is provided a liquid stor2ge tank contents gauge comprising me2nS
providlng an electrical signal corresponding to the vertical height o the liquid in a tankS electronic means for deriving the volume of liquid cor-responding to said vertical height, and an output means for providing a visual out~ut of said volume.
Preferred embodiments of the ~resent invention will now be described with reference to the accomL~anying d~a-.Jings in which:
~igvrQ~ 1a and 1b form Fi~ure 1 ~!~hich is a partial~y sectioned slde view o the sensing unit of the gaugre according to the present inventiorl shown installed in a tanX.
Figure 2 is a cross section of the ~au.ge taken along the line ~.-A in l~igl,lre lb.
~5 ~igure '~ is a block dia~ram o an electronic circuit associated ~ith the ~au~e of t~e preseL~t invention.
~ ~e d is a block diagr~m of ar alternative electronic circuit e.r~olo~r:inG a microprocessor.
r~he sensin~ iO sho~r. in ~ig~e 1 comLr.rises an el.onsate JO t~ e 11 J at the lc~er end of ~hich is m~o~nted an ~Ltraso~lc - 2 - ~ , .
)4'~1 transducer 12. The tube 11 i5 suspended inside the tank for which the contents are to be gau~ed ana the length of the tube 11 is chosen such that the transducer 12 is positioned at, or close to, the bottom of the tanX. ~he transducer is orientated such tb~t its signal is propagated vertically upwards inside the tube to the surface of the liquid stored in the tank.
Holes 1~ in the tube 11 allow the liquid to enter the tube 11 and ~or the liquid level to correspond to the level in the tank.
The type of mou~ting just described with the transducer - 10 inside the tube has the advantage that the transducer is protected ~rom damage during install~tion or by falling objects. Severe blows could also cause it to produce high voltages due to the piezoelectric effect. Ho~ever in some situations it is preferable to adopt some other form of mounting such as fi~ing the transducer to the upper surface of a horizontal plate posltioned at the bottom of the tank.
It is also possible to mount the transducer ou-tside but in contact with the bottom of the tank. 3uch a configuration reduces the strength of the echo signal received, requiring e~tra amplification, but can be a much simpler mechanical arrangement. With large tanks, mounting the transducer and adjusting its orientation from the top by a long rod or similar device may be inconvenient and entry via a hole in the side of the tank near the bottom may be more appropriate.
As sho~n in Figure 3, the signal to the transducer 12 is supplied from an oscillator 14 via a frequency divider 15, a pulse sha~er circuit 16 and a modulator 17. A second oscillator 1~ controls the modulztor 17 such that signal passed to the transducer 12 is in the form of pulses each ll;~V41~1 composed of a burst several cycles long, at regular intervals.
This signal is passed to the transducer via a power amplifler 19.
An example of a transducer used in practice is a lead 5 zirconote titanate disc having a resonant frequency of 500 KHz.
l~lhen the ultransonic signal reaches the liquid surface some of its energy, at least, is reflected by the liquid/air interface and returns to the transducer 12. This reflected signal is converted back into electrical form by the transducer and amplified by amplifier 20. The time taken by the signal to travel to the surface and return to the trans-ducer 12 ~ equal to twice the depth divided by the velocity of propagation of the ultransonic wavesO Thls velocity is a constant for any particular li~uid and hence the depth ^an be readily calculated if the time is measured. o measure the time interval between transmission of a burst and reception of its echo, circuitry is arranged to count the n~mber of pulses of a high frequency pulse train of known repetition rate that occur during this interval. This count is referred to as C1. To avoid ambiguity the rate of transmission of signal bursts is sufficiently low to ensure that, even with maximum liquid depth, the echo returns to the transducer before the next signal is transmitted.
The signal from amplifier 20 is passed through a detector circuit 21 and a second amplifler 22. The output of amplifier 22 is fed to a gating waveform generator 23 as a reset signal, the other input to the generator 23 being derived from the output of the pulse shaper circuit 16.
The ga~ing generator 23 acts to control a gate 24 ~Thich gates 30 the pulses from the osclllator 14 which are operating a 11~0~
counter 25.
In applica~ons where the temperature of the stored liquid is subject to variation, compensa-tion for the change of velocity of propagation of ultrasonic waves with temperature is ircluded. ~he temperature is measured by a sensor such as a thermistor, a thermocouple or a resistance thermometer 29 and the electrical signal produced controls a voltage controlled oscillator.
The number of cycles of the ouput of tnis oscillator occurring in the time interval between tranmission of a burst and reception of its echo is counted~ This count c2 is added to the count c1 referred to above, o~ the constant frequency. The relationship between temperature and frequency of the voltage controlled oscillator is arranged so that the total count, c - (c1 ~ c2), for a particular depth, does not vary if the ~trasonic velocity changes ~"ith temperature.
The total count c occurring in the time interval between transmission of a burst of ultrasonic energy and the reception of its echo is a direct measure of the liquid depth. When the liquid is contained in a tank o~ non constant cross sectional area that varies with depth, the relationship between depth and volume is non-linear. This is a common occurrence in many types of storage tank. ~or e~ample, petrol is frequently kept in cylindrical tænks mounted with their axes in a horizontal plane.
To convert from depth to volume, program~a3le read only memory (PROrI) stores 26 are used. The number of high frequency pulses occurring du~ing the transmlsslon to echo reception interval is obtalned in binary orm as an output from counter 25 V4'~1 and is used as the input address to a store. ~he output of a store for ar~ particular input, is the corresponding volume in binary form. This is converted into bir~ry coded decimal format by decoder and decade driver circuits 27 and used to drive a decimal display 28 indicating the stored vol~e. To allow alternative readout in either gallons or litres, two sets of progr~ ble read only me~ories are used and either can be switched into operation.
The vertical diameter of the tank is quant~edinto 1~ more than 1000 equal segments. Thus by making the systèm sense changes of le~el at least as small as one of these segments an accuracy of better than 0.17? is obtaired.
Correspondirg to each of the possible liquid heights is a 16 bit word representing the appropriate volume of liquid.
Each word has to be 16 bits long because the display has ~our main decades each requiri~ a 4 bit BCD (binary coded decima]) input.
An example of suitable PROM units are those manufactured by Signetics (type 92S115) and are 4096 bit Bipolar devices organised as 512x8 bytes, Since 1000x15 words are required.
~our 82S115 units are r`equired per instrument to read gallons.
As a gallon/litres option is included another four are incorporated.
A printout facility may also be included that allows the operator to h~ve the liquid volume recorded on a roll of paper. The printing ~echanism is supplied with a similar signal to that which actuates the declmal display but only operates ~hen required by the operator, To indicate ~lhen the tar~ is full a ~arning alarm is also pro-v-ided. This is operated by a c-rcuit that detects .
ll;~V~
when the n~be~ in t,le binary cc~nter 25, operating over the time i.n-ter~-al bet~een the trans~.ittea signal and the echo retl~n, rea.ches a predetermined :Level. The alarm can take the I Ol'm o F a light or an audiblesound or both and is principcllly of use durinS the ope~ation of filling tanks, In so~e applications the signal processing may be carried out bv using a microprocessor instead of dedicated digital circuits, as shown in Figure 4. With the microprocessor system the compensation for the variation of ultrasonic ~Locity with temperat~re may be achieved b~
multiplying the apparent depth of liquid, as derived from the time int2rval between the trans~itted and echo pulses, by a correction factor. The appropriate factor is selected from the system memor~r by addressing the latter ~ith the digitised output of the temperature sensor. ~his .nethod of compensation is used instead of the one described earlier in T.~hich a voltage depenclent oscillator is controlled by an analog~le signal correspondin~ -to temperature.
A variation in the method of converting from depth to vol~e ~,Then a microprocessor is incorpora~ed is also appropriate in some circumstances, ins-tead of storin~ all the pairs of values of depth/volume ~-1antities in a PRO~i memory.
~s shoT;~n in Figure 4 7 the signal to the transducer 12 is derived .-.ro~ a signal genera~or 3~ eauivalent to the oscillator -i~ eqllenc,r divider 15, pu~1se sh~er15 and mod-~lator 17 controlled b~ oscillator 18, and is ampliIied ~y ~lr)lifier 19 as be,?ore, In ad.lition each p~se lron the siglal generator 30 is fed to a microprocessor 31 'jO 2ncl th.e ret~r. p-ulse is also fed to the microprocessor 31 V4 ~1 via amp]if,-i*.r 20 and detector circuit 21. A signal from the temperatllre sensor 29 :is ~lso fed to the micro-processor 31 a.nd the variation -in the propagation velocity ~rith tem~erature are automaticall.y compe~sated for.
The microprocessor i9 ~)rogra~med to calcula-te the volume from the tank dilnensions and the measured depth.
With ~ome t.ank shapes however, a readily computable rel~tionship between depth and ~olume cannot be obtained and a combin2tion of the two methods of (a) storing all the depth/volume pairs, and (b) calculating the volume each time is used. The corresponding values of depth and volume for a number o-f depths between the minimum and maximum are held in store. The values of volwme for intermediate depths are obtained by interpolation. ~inear interpolation is used when the reference de~ths areIairly close together or the volume/depth relationship does not depart greatly from lin~rand higher order interpolation schemes are used in other cases as appro~riate~ The output from the microprocessor ~1 is fed to a visual d~splay 32.
In ~ome si~uations, especially when tanks are used for petrol stora~e, water can collect in the bottom of a tank. ~ecause its den~ity is ~greater th.an that of petrol and also bec~use o~ chemical differencesinhibitin~ -their ml.~ing, the ]iqui.ds form two layers wJith the water belo~.
~ warnir,~ mechanism is in~.. uded to indica-te when the le~el o-E the ~wanted water e.~ceeds a cert~in nredetermined thre~'1old, The 1iater e~ensing mechanism com~rises a pair o-f concentric annular C~CitOl' pl.ate~ 42 mo~u~ted i~lside the -tube 11 a
Enown designs o-f gauge can only be used ~,lith tanks of one parti~u~a~ shaL~e and size and re-calibration for ta-nks of other shapes and sizes is difficuLt.
According to the present invention there is provided a liquid stor2ge tank contents gauge comprising me2nS
providlng an electrical signal corresponding to the vertical height o the liquid in a tankS electronic means for deriving the volume of liquid cor-responding to said vertical height, and an output means for providing a visual out~ut of said volume.
Preferred embodiments of the ~resent invention will now be described with reference to the accomL~anying d~a-.Jings in which:
~igvrQ~ 1a and 1b form Fi~ure 1 ~!~hich is a partial~y sectioned slde view o the sensing unit of the gaugre according to the present inventiorl shown installed in a tanX.
Figure 2 is a cross section of the ~au.ge taken along the line ~.-A in l~igl,lre lb.
~5 ~igure '~ is a block dia~ram o an electronic circuit associated ~ith the ~au~e of t~e preseL~t invention.
~ ~e d is a block diagr~m of ar alternative electronic circuit e.r~olo~r:inG a microprocessor.
r~he sensin~ iO sho~r. in ~ig~e 1 comLr.rises an el.onsate JO t~ e 11 J at the lc~er end of ~hich is m~o~nted an ~Ltraso~lc - 2 - ~ , .
)4'~1 transducer 12. The tube 11 i5 suspended inside the tank for which the contents are to be gau~ed ana the length of the tube 11 is chosen such that the transducer 12 is positioned at, or close to, the bottom of the tanX. ~he transducer is orientated such tb~t its signal is propagated vertically upwards inside the tube to the surface of the liquid stored in the tank.
Holes 1~ in the tube 11 allow the liquid to enter the tube 11 and ~or the liquid level to correspond to the level in the tank.
The type of mou~ting just described with the transducer - 10 inside the tube has the advantage that the transducer is protected ~rom damage during install~tion or by falling objects. Severe blows could also cause it to produce high voltages due to the piezoelectric effect. Ho~ever in some situations it is preferable to adopt some other form of mounting such as fi~ing the transducer to the upper surface of a horizontal plate posltioned at the bottom of the tank.
It is also possible to mount the transducer ou-tside but in contact with the bottom of the tank. 3uch a configuration reduces the strength of the echo signal received, requiring e~tra amplification, but can be a much simpler mechanical arrangement. With large tanks, mounting the transducer and adjusting its orientation from the top by a long rod or similar device may be inconvenient and entry via a hole in the side of the tank near the bottom may be more appropriate.
As sho~n in Figure 3, the signal to the transducer 12 is supplied from an oscillator 14 via a frequency divider 15, a pulse sha~er circuit 16 and a modulator 17. A second oscillator 1~ controls the modulztor 17 such that signal passed to the transducer 12 is in the form of pulses each ll;~V41~1 composed of a burst several cycles long, at regular intervals.
This signal is passed to the transducer via a power amplifler 19.
An example of a transducer used in practice is a lead 5 zirconote titanate disc having a resonant frequency of 500 KHz.
l~lhen the ultransonic signal reaches the liquid surface some of its energy, at least, is reflected by the liquid/air interface and returns to the transducer 12. This reflected signal is converted back into electrical form by the transducer and amplified by amplifier 20. The time taken by the signal to travel to the surface and return to the trans-ducer 12 ~ equal to twice the depth divided by the velocity of propagation of the ultransonic wavesO Thls velocity is a constant for any particular li~uid and hence the depth ^an be readily calculated if the time is measured. o measure the time interval between transmission of a burst and reception of its echo, circuitry is arranged to count the n~mber of pulses of a high frequency pulse train of known repetition rate that occur during this interval. This count is referred to as C1. To avoid ambiguity the rate of transmission of signal bursts is sufficiently low to ensure that, even with maximum liquid depth, the echo returns to the transducer before the next signal is transmitted.
The signal from amplifier 20 is passed through a detector circuit 21 and a second amplifler 22. The output of amplifier 22 is fed to a gating waveform generator 23 as a reset signal, the other input to the generator 23 being derived from the output of the pulse shaper circuit 16.
The ga~ing generator 23 acts to control a gate 24 ~Thich gates 30 the pulses from the osclllator 14 which are operating a 11~0~
counter 25.
In applica~ons where the temperature of the stored liquid is subject to variation, compensa-tion for the change of velocity of propagation of ultrasonic waves with temperature is ircluded. ~he temperature is measured by a sensor such as a thermistor, a thermocouple or a resistance thermometer 29 and the electrical signal produced controls a voltage controlled oscillator.
The number of cycles of the ouput of tnis oscillator occurring in the time interval between tranmission of a burst and reception of its echo is counted~ This count c2 is added to the count c1 referred to above, o~ the constant frequency. The relationship between temperature and frequency of the voltage controlled oscillator is arranged so that the total count, c - (c1 ~ c2), for a particular depth, does not vary if the ~trasonic velocity changes ~"ith temperature.
The total count c occurring in the time interval between transmission of a burst of ultrasonic energy and the reception of its echo is a direct measure of the liquid depth. When the liquid is contained in a tank o~ non constant cross sectional area that varies with depth, the relationship between depth and volume is non-linear. This is a common occurrence in many types of storage tank. ~or e~ample, petrol is frequently kept in cylindrical tænks mounted with their axes in a horizontal plane.
To convert from depth to volume, program~a3le read only memory (PROrI) stores 26 are used. The number of high frequency pulses occurring du~ing the transmlsslon to echo reception interval is obtalned in binary orm as an output from counter 25 V4'~1 and is used as the input address to a store. ~he output of a store for ar~ particular input, is the corresponding volume in binary form. This is converted into bir~ry coded decimal format by decoder and decade driver circuits 27 and used to drive a decimal display 28 indicating the stored vol~e. To allow alternative readout in either gallons or litres, two sets of progr~ ble read only me~ories are used and either can be switched into operation.
The vertical diameter of the tank is quant~edinto 1~ more than 1000 equal segments. Thus by making the systèm sense changes of le~el at least as small as one of these segments an accuracy of better than 0.17? is obtaired.
Correspondirg to each of the possible liquid heights is a 16 bit word representing the appropriate volume of liquid.
Each word has to be 16 bits long because the display has ~our main decades each requiri~ a 4 bit BCD (binary coded decima]) input.
An example of suitable PROM units are those manufactured by Signetics (type 92S115) and are 4096 bit Bipolar devices organised as 512x8 bytes, Since 1000x15 words are required.
~our 82S115 units are r`equired per instrument to read gallons.
As a gallon/litres option is included another four are incorporated.
A printout facility may also be included that allows the operator to h~ve the liquid volume recorded on a roll of paper. The printing ~echanism is supplied with a similar signal to that which actuates the declmal display but only operates ~hen required by the operator, To indicate ~lhen the tar~ is full a ~arning alarm is also pro-v-ided. This is operated by a c-rcuit that detects .
ll;~V~
when the n~be~ in t,le binary cc~nter 25, operating over the time i.n-ter~-al bet~een the trans~.ittea signal and the echo retl~n, rea.ches a predetermined :Level. The alarm can take the I Ol'm o F a light or an audiblesound or both and is principcllly of use durinS the ope~ation of filling tanks, In so~e applications the signal processing may be carried out bv using a microprocessor instead of dedicated digital circuits, as shown in Figure 4. With the microprocessor system the compensation for the variation of ultrasonic ~Locity with temperat~re may be achieved b~
multiplying the apparent depth of liquid, as derived from the time int2rval between the trans~itted and echo pulses, by a correction factor. The appropriate factor is selected from the system memor~r by addressing the latter ~ith the digitised output of the temperature sensor. ~his .nethod of compensation is used instead of the one described earlier in T.~hich a voltage depenclent oscillator is controlled by an analog~le signal correspondin~ -to temperature.
A variation in the method of converting from depth to vol~e ~,Then a microprocessor is incorpora~ed is also appropriate in some circumstances, ins-tead of storin~ all the pairs of values of depth/volume ~-1antities in a PRO~i memory.
~s shoT;~n in Figure 4 7 the signal to the transducer 12 is derived .-.ro~ a signal genera~or 3~ eauivalent to the oscillator -i~ eqllenc,r divider 15, pu~1se sh~er15 and mod-~lator 17 controlled b~ oscillator 18, and is ampliIied ~y ~lr)lifier 19 as be,?ore, In ad.lition each p~se lron the siglal generator 30 is fed to a microprocessor 31 'jO 2ncl th.e ret~r. p-ulse is also fed to the microprocessor 31 V4 ~1 via amp]if,-i*.r 20 and detector circuit 21. A signal from the temperatllre sensor 29 :is ~lso fed to the micro-processor 31 a.nd the variation -in the propagation velocity ~rith tem~erature are automaticall.y compe~sated for.
The microprocessor i9 ~)rogra~med to calcula-te the volume from the tank dilnensions and the measured depth.
With ~ome t.ank shapes however, a readily computable rel~tionship between depth and ~olume cannot be obtained and a combin2tion of the two methods of (a) storing all the depth/volume pairs, and (b) calculating the volume each time is used. The corresponding values of depth and volume for a number o-f depths between the minimum and maximum are held in store. The values of volwme for intermediate depths are obtained by interpolation. ~inear interpolation is used when the reference de~ths areIairly close together or the volume/depth relationship does not depart greatly from lin~rand higher order interpolation schemes are used in other cases as appro~riate~ The output from the microprocessor ~1 is fed to a visual d~splay 32.
In ~ome si~uations, especially when tanks are used for petrol stora~e, water can collect in the bottom of a tank. ~ecause its den~ity is ~greater th.an that of petrol and also bec~use o~ chemical differencesinhibitin~ -their ml.~ing, the ]iqui.ds form two layers wJith the water belo~.
~ warnir,~ mechanism is in~.. uded to indica-te when the le~el o-E the ~wanted water e.~ceeds a cert~in nredetermined thre~'1old, The 1iater e~ensing mechanism com~rises a pair o-f concentric annular C~CitOl' pl.ate~ 42 mo~u~ted i~lside the -tube 11 a
3~ fe~ inches above the -tr.ansd-lcer 12. ~he ~resence of tiater B
ll~V'~
is detected by sensin~ a change in the capaci-tance between the plates 42, -the dielectric constan-ts of fuel, oil or petrol and water bein~T, different, When water is presen-t in the bottom of a tank containing~
llquid o~ a lower dielectric constant, it increases the capacitance of the open plate capacitor i-ormed by the plates 42- This capacit~nce controls the frequency of a squarewave oscillator to an inverse relationship and so the presence of water decreases the frequency. Each cycle of the oscillator output triggers a mono~able circuit producing pulses of fixed duration, These are integrated and smoothed to produce a direct voltage. When the value of this voltage drops below a preset thresilold value, an alarm is activa-ted.
This a~arm ma~ take the form of a audible warning, a visible light or both.
'~he tu~e 11 is mo~nted on an assembly 33 which allows the axis of the tube 11 to be aligned truly vertical. The assembly is screwed into the top of the tank by a cap 34 with screw thread 3~. To allow adjustment of the assembly 33 permittin~ the axis of the transducer to be positioned at right angles to the liauid surface the tube 11 is secured to a plate 36.
Plate 36 is suspen~ed from cap 34 by threaded set screws 37. Springs 38 positively hold cap 34 and late 36 apart, Screws 37 are in tapped holes in cap 34 and turning any ons of them ~lters its vertical positlon. Adjusting all three screws to~,ether rai~es or lowers plate 36 but alte-ring any one or t~io of -them ~lso varie, the angle the axis of tran~llcer a~ n~l~r 12 ~akes with the horizontal surface of the ~ i(l, To ~btail maxi~llm re~3~?cted sigral the 11~0 441 transducer a,cis is ad,justed to be vertical. Locking nuts 37 are then ti;.htened to maintaln this positioning, The t:r.~nsducer 12 ~ 1 the capaci~or plates 42 are connec-ted to external electrical control equipment by way of coa.~i~l cabLes 3~ whi.ch pass up inside the tube 11 to a cable conduit 39 secured to the ca 34 , The tube 11 is earthed by ~ay of ear~h tags 40 wh:ich are co.nnec-ted to an earth terminal stud 4-l from where an earthin~ conductor passes to the cable conduit 39.
In an alternative construction, the tube 11 is connected to a trunnion ring at two diameterically opposite points ~rhich allows the tube to swing i.n a vertical plane relative to thetr~on ring. The trunnion ring i~self is pivoted in a housing about an a~is at right angles to the pivotal axis between the tube and the ring. The housing is secured to the tank by wa,y of an ad~ustable threaded mount. ~he trunnion ring acts as ~ gimbel mountlng ~hich allows the tube 11 to hang truly vertical. Such a mounting is especially suitable for situations ~rhere the tanlc may be +ilted, as for example in mobile applications~
When the liquid level sensor is to be used in a large capacity, vertical cyli.ndrical bulk storage tank, the sensor unit is preferabLy ~ounted on the side of the tank~ adjacent its lo;ler end to avoid the use of a tube 1t of an impracticably long len~th. In this situtation some form o~ pivoting connection is utili~.ed -to allo~ the transducer axis to be aligned truly ver-tica:l .
For ~nlic~tions ~!here t~le tar,k containing the liquid may be tilted (e~c~,. in mobile tar.kers) tne be~ from an ultrasonic tr~nsducer l~ay not arrive ?er~endicular to the surface~
In such sl 't~a'ti ons a cap,~cltl~e sensor :is preferab1..e, _ 10 -B
1~ ~V'~41 The eiez-trodesof such a capacitor ~ransducer are so arra.1ged that the dielectric space between them is increas~ngly filled ~ith the liauid to be measured as its level rises. As its dielectric constant is different to that o-~ air the capacitance changes with level. Some electrode configurations used are (a) ver~ical coaxial cylinders, (b) a double helix of metallic stri or wire, (c) vertical parallel p]ates (d) interleaved 'fingers' o~ metal deposited on an insulating material.
To measure liquid depth the output of a high stability, constant ~requency oscilla~or is counted for a time depending on the capacitance sensed. The count is used to read out the corresponding vol~ne as described earlier. In some instruments the depth dependent capacitance is used as the ~requency determining element in an oscillator whose output is counted for a fi~ed ti~,e but this is merely an alternative cir cuit arrangement lor producing a count dependent on depth.
ll~V'~
is detected by sensin~ a change in the capaci-tance between the plates 42, -the dielectric constan-ts of fuel, oil or petrol and water bein~T, different, When water is presen-t in the bottom of a tank containing~
llquid o~ a lower dielectric constant, it increases the capacitance of the open plate capacitor i-ormed by the plates 42- This capacit~nce controls the frequency of a squarewave oscillator to an inverse relationship and so the presence of water decreases the frequency. Each cycle of the oscillator output triggers a mono~able circuit producing pulses of fixed duration, These are integrated and smoothed to produce a direct voltage. When the value of this voltage drops below a preset thresilold value, an alarm is activa-ted.
This a~arm ma~ take the form of a audible warning, a visible light or both.
'~he tu~e 11 is mo~nted on an assembly 33 which allows the axis of the tube 11 to be aligned truly vertical. The assembly is screwed into the top of the tank by a cap 34 with screw thread 3~. To allow adjustment of the assembly 33 permittin~ the axis of the transducer to be positioned at right angles to the liauid surface the tube 11 is secured to a plate 36.
Plate 36 is suspen~ed from cap 34 by threaded set screws 37. Springs 38 positively hold cap 34 and late 36 apart, Screws 37 are in tapped holes in cap 34 and turning any ons of them ~lters its vertical positlon. Adjusting all three screws to~,ether rai~es or lowers plate 36 but alte-ring any one or t~io of -them ~lso varie, the angle the axis of tran~llcer a~ n~l~r 12 ~akes with the horizontal surface of the ~ i(l, To ~btail maxi~llm re~3~?cted sigral the 11~0 441 transducer a,cis is ad,justed to be vertical. Locking nuts 37 are then ti;.htened to maintaln this positioning, The t:r.~nsducer 12 ~ 1 the capaci~or plates 42 are connec-ted to external electrical control equipment by way of coa.~i~l cabLes 3~ whi.ch pass up inside the tube 11 to a cable conduit 39 secured to the ca 34 , The tube 11 is earthed by ~ay of ear~h tags 40 wh:ich are co.nnec-ted to an earth terminal stud 4-l from where an earthin~ conductor passes to the cable conduit 39.
In an alternative construction, the tube 11 is connected to a trunnion ring at two diameterically opposite points ~rhich allows the tube to swing i.n a vertical plane relative to thetr~on ring. The trunnion ring i~self is pivoted in a housing about an a~is at right angles to the pivotal axis between the tube and the ring. The housing is secured to the tank by wa,y of an ad~ustable threaded mount. ~he trunnion ring acts as ~ gimbel mountlng ~hich allows the tube 11 to hang truly vertical. Such a mounting is especially suitable for situations ~rhere the tanlc may be +ilted, as for example in mobile applications~
When the liquid level sensor is to be used in a large capacity, vertical cyli.ndrical bulk storage tank, the sensor unit is preferabLy ~ounted on the side of the tank~ adjacent its lo;ler end to avoid the use of a tube 1t of an impracticably long len~th. In this situtation some form o~ pivoting connection is utili~.ed -to allo~ the transducer axis to be aligned truly ver-tica:l .
For ~nlic~tions ~!here t~le tar,k containing the liquid may be tilted (e~c~,. in mobile tar.kers) tne be~ from an ultrasonic tr~nsducer l~ay not arrive ?er~endicular to the surface~
In such sl 't~a'ti ons a cap,~cltl~e sensor :is preferab1..e, _ 10 -B
1~ ~V'~41 The eiez-trodesof such a capacitor ~ransducer are so arra.1ged that the dielectric space between them is increas~ngly filled ~ith the liauid to be measured as its level rises. As its dielectric constant is different to that o-~ air the capacitance changes with level. Some electrode configurations used are (a) ver~ical coaxial cylinders, (b) a double helix of metallic stri or wire, (c) vertical parallel p]ates (d) interleaved 'fingers' o~ metal deposited on an insulating material.
To measure liquid depth the output of a high stability, constant ~requency oscilla~or is counted for a time depending on the capacitance sensed. The count is used to read out the corresponding vol~ne as described earlier. In some instruments the depth dependent capacitance is used as the ~requency determining element in an oscillator whose output is counted for a fi~ed ti~,e but this is merely an alternative cir cuit arrangement lor producing a count dependent on depth.
Claims (9)
1. A liquid storage tank contents gauge comprising ultrasonic signal means for providing an electrical signal cor-responding to the vertical height of the liquid in a tank, elec-tronic means coupled to said signal means for deriving the volume of liquid corresponding to said vertical height, and an output means coupled to said electronic means for providing a usable output of said volume, said ultrasonic signal means including one and only one transducer for both emitting a signal and re-ceiving the same signal when reflected by a liquid-air interface in a tank, said electronic means comprising a plurality of pro-grammable read-only memory units, each containing the value of a liquid volume corresponding to a given vertical height in said tank and means for searching for and finding the read-only memory unit corresponding to the vertical height provided by said sig-nal, and means for passing the output of said read-only memory unit to said output means.
2. A gauge as claimed in claim 1, wherein said one and only one transducer is an ultrasonic transducer, there are means for mounting said one and only one transducer at the base of a tank to emit a pulse of ultrasonic energy vertically up-wards and to detect the same pulse when reflected from a liquid/
air interface within a tank, and timing means for timing the interval between the emission of a pulse and the detection of the reflected same pulse by said one and only one transducer.
air interface within a tank, and timing means for timing the interval between the emission of a pulse and the detection of the reflected same pulse by said one and only one transducer.
3. A gauge as claimed in claim 2, wherein said timing means includes a counter which is started at the instant that a pulse is emitted by said one and only one transducer and is stopped at the instant that reflected same pulse is detected by said one and only one transducer.
4. A gauge as claimed in claim 1, wherein said elec-tronic means comprises a microprocessor programmed to compute the volume of liquid corresponding to the said electrical signal.
5. A gauge as claimed in claim 1, wherein said usable output is a visual output.
6. A liquid storage tank contents gauge comprising signal means for providing a first electrical signal correspond-ing to the vertical height of the liquid in a tank, said signal means including one and only one transducer, electronic means coupled to said one and only one transducer of said signal means for deriving the volume of liquid corresponding to said vertical height, an output means coupled to said electronic means for providing a visual output of said volume, said electronic means including means for producing a second-electrical signal in-dicative of the temperature of the liquid in the tank, and means for modifying said first electrical signal by adding said second electrical signal to said first electrical signal so as to com-pensate for temperature variations.
7. A liquid storage tank contents gauge comprising signal means for providing an electrical signal corresponding to the vertical height of the liquid in a tank, electronic means coupled to said signal means for deriving the volume of liquid corresponding to said vertical height, and an output means coupled to said electronic means for providing a visual output of said volume, and means separately mountable in such tank for detecting the presence of a layer of contaminating second liquid immiscible with and of greater density than the liquid to be stored in the tank, said means for detecting the presence of a layer of contaminating second liquid including a pair of capacitor plates, means for mounting said capacitor plates ad-jacent the base of such tank, and means connected to said capacitor plates for detecting the change in capacitance between said plates indicating the presence of said second liquid.
8. A liquid storage tank contents gauge as claimed in claim 7, wherein said means for detecting the presence of a layer of contaminating second liquid also includes means for providing a warning when the depth of said contaminating liquid exceeds a given value.
9. A liquid storage tank contents gauge comprising signal means including one and only one transducer for pro-viding a first electrical signal corresponding to the vertical height of the liquid in a tank, electronic means coupled to said signal means for deriving the volume of liquid corresponding to said vertical height, an output means coupled to said elec-tronic means for providing a usable output of said volume said gauge having compensating means to compensate for variations in the temperature of the liquid in the tank, said compensating means including means for producing a second electrical signal indicative of the temperature of the liquid in the tank, and means for modifying said first electrical signal by adding said second electrical signal to said first electrical signal.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB315677A GB1600131A (en) | 1977-01-26 | 1977-01-26 | Liquid storage tank contents gauge |
| GB3156/77 | 1977-01-26 | ||
| GB3352177 | 1977-08-10 | ||
| GB33521/77 | 1977-08-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1130441A true CA1130441A (en) | 1982-08-24 |
Family
ID=26238100
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA295,662A Expired CA1130441A (en) | 1977-01-26 | 1978-01-25 | Liquid storage tank contents gauge |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS53101463A (en) |
| CA (1) | CA1130441A (en) |
| DE (1) | DE2803374A1 (en) |
| FR (1) | FR2379056A1 (en) |
| NL (1) | NL7800887A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2932243C2 (en) * | 1979-08-09 | 1982-04-22 | Eugen 2805 Stuhr Rapp | Level and temperature measuring device for tank systems |
| GB2084322B (en) * | 1980-09-18 | 1984-08-30 | Avery Hardoll Ltd | Fluid measuring system |
| US4448207A (en) * | 1981-11-03 | 1984-05-15 | Vital Metrics, Inc. | Medical fluid measuring system |
| FR2522139A1 (en) * | 1982-02-22 | 1983-08-26 | Thomson Brandt | Liq. volume measuring appts. for e.g. motor vehicle IC engine - uses microprocessor controlled electromagnetic transducer to apply vibrations to elastic medium inside tube immersed in liq. |
| US5095747A (en) * | 1989-12-26 | 1992-03-17 | Barnstead Thermolyne Corporation | Cryogenic liquid level sensing apparatus |
-
1978
- 1978-01-25 NL NL7800887A patent/NL7800887A/en not_active Application Discontinuation
- 1978-01-25 FR FR7802080A patent/FR2379056A1/en not_active Withdrawn
- 1978-01-25 CA CA295,662A patent/CA1130441A/en not_active Expired
- 1978-01-26 JP JP677178A patent/JPS53101463A/en active Pending
- 1978-01-26 DE DE19782803374 patent/DE2803374A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| DE2803374A1 (en) | 1978-07-27 |
| NL7800887A (en) | 1978-07-28 |
| JPS53101463A (en) | 1978-09-04 |
| FR2379056A1 (en) | 1978-08-25 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |