US00756257OB2

(12) United States Patent (10) Patent No.: US 7.562,570 B2

Peters (45) Date of Patent: Jul. 21, 2009
(54) ULTRASONIC OIL/WATER TANKLEVEL 5,131.271 A * 7/1992 Haynes et al. ............ 73,290 V
MONITOR HAVING WIRELESS 6,967,589 B1 * 1 1/2005 Peters ..................... 340,854.6
TRANSMISSION MEANS k .
cited by examiner
(75) Inventor: George W. Peters, Newport Beach, CA Primary Examiner Hezron Williams
(US) Assistant Examiner Tamiko D Bellamy
(74) Attorney, Agent, or Firm Morland C. Fischer
(73) Assignee: Oleum Tech Corporation, Irvine, CA
(US) (57) ABSTRACT
(*) Notice: Subject to any disclaimer, the term of this An ultrasonic monitor to measure the level of a fluid (e.g., oil
patent is extended or adjusted under 35 or water) within a storage tank. The ultrasonic monitor is
U.S.C. 154(b) by 92 days. Surrounded by a gas-tight, explosion-proof casing that is
coupled to the top of the tank so that the acoustic axis of a
(21) Appl. No.: 11/373,779 (e.g., 59 KHZ) ultrasonic transducer is directed downwardly
towards the surface of the fluid. The ultrasonic transducer is
(22) Filed: Mar 13, 2006 encased within a protective (e.g., Delrin) housing so as to
O O resist the hostile (e.g., acidic, gaseous vapors and extreme
(65) Prior Publication Data temperature) via within E. tank. A R CPU is inter
US 2007/0209.434 A1 Sep. 13, 2007 connected between the ultrasonic transducer and an RF trans
ceiver having an antenna from which fluid level data calcu
(51) Int. Cl. lated by the main CPU can be transmitted over a wireless
GOIF 23/28 (2006.01) communication path. A reference rod having at least one
(52) U.S. Cl. .................................................... T3/290 V acoustic reflector located at a known distance therealong
(58) Field of Classification Search ............... 73/290 V; extends downwardly from the housing of the ultrasonic trans
342/124; 116/227; 367/908, 98 ducer towards the surface of the fluid. The main CPU is
See application file for complete search history. responsive to the time of flight between incident signals gen
erated by the acoustic transducer and return and echo signals
(56) References Cited reflected off the surface of the fluid and the acoustic reflector
U.S. PATENT DOCUMENTS for calculating the corresponding distance between the fluid
and the transducer. The main CPU is adapted to adjust the
4,470,299 9, 1984 Soltz ........................ 73,290 V time of flight to compensate for errors introduced by the
4.487,065 12, 1984 Carlin et al. .............. 73,290 V environment (e.g., gas vapors, pressure, etc.) of the tank
4,523,460 6, 1985 Strickler et al. ............... T3,200
4,578,997 4, 1986 SoltZ ........... ... 3,290 V depending upon the echo signal that is reflected to the acous
4.675,854 6, 1987 Lau ............................. 367/98 tic transducer by the reflector of the reference rod.
4,868,797 9, 1989 Soltz ........................... 367/98
4,928,525 5, 1990 Aderholt et al. . 73,290 V 27 Claims, 7 Drawing Sheets

MEMORY 52
RAMORFASH
SERAL

is MN o's W
READ ANK D

POWER supply
step Up
REGULATORS
CURRENT
3rd output on

27
ov g 35, 27
FLUD MONTOR 7- - - - - - -
------ - - -
U.S. Patent Jul. 21, 2009 Sheet 1 of 7 US 7.562,570 B2

F.G. 6
U.S. Patent Jul. 21, 2009 Sheet 2 of 7 US 7.562,570 B2
U.S. Patent Jul. 21, 2009 Sheet 4 of 7 US 7.562,570 B2

t
:
X
H
Y
d
e
-

8
U.S. Patent Jul. 21, 2009 Sheet 5 Of 7 US 7.562,570 B2

66

sees
C
CSEs
- FA
s 5
C

FG, 8
U.S. Patent Jul. 21, 2009 Sheet 6 of 7 US 7.562,570 B2

O
SET PING COUNT = O BEGIN
O2 O3
MEASURE TEMPERATURE
O4
SEND PING BASED ON CURRENT
PULSE WIDTH SETTING
O5
CAL CULATE ROUNDTRIPTIME WITH
TEMPERATURE COMPENSATION

CLASSIFY FNG. RETURN BASED ON AMPLTUDE

IO8

INCREASE Tx FPULSE
WIDTH AND VOLTAGE
NO
O9 O

RETURNTOO HIGH YES DECREASE Tx PULSE

P WDTH AND VOLTAGE

TAUTO ADJUST INCREMENT PING COUNT

4.

(RTT-RTT2) RETURN
MNIMUM MAX(RTT, RTT2)
QEFEyes
RETURN
MIN MUM MAXCRTT,RTT3)
9

RETURN
FIG. OA No ( MAX(RTT2RTT3)
INDICATE MISS
2O 22 (GOTOAUTOEVEL
CALIBRATION
U.S. Patent Jul. 21, 2009 Sheet 7 Of 7 US 7.562,570 B2

AUTO LEVEL
CALIBRATION 24

FIND 8 FOOT 25
REFERENCE ECHO 29

CAL CULATE
YES SPEED OF SOUND
26 ERROR AND ADJUST
RECEIVED VALUE

27 FIND 4 FOOT
REFERENCE ECHO

CAL CULATE
28 G SPEED OF SOUND
ERROR AND ADJUST
3. RECEIVED VALUE

SET CORRECTION

32 RETURN RECEIVED
VALUE

33

FG, OB
 US 7,562,570 B2
1. 2
ULTRASONIC OL/WATER TANKLEVEL Accordingly, it would be desirable to have a low mainte
MONITOR HAVING WIRELESS nance, battery powered ultrasonic oil level monitor that is
TRANSMISSION MEANS encased in a gas tight/explosion proof casing which can be
quickly and easily coupled to a storage tank and that is
BACKGROUND OF THE INVENTION adapted to transmit highly accurate oil level data to a location
outside the explosive environment of the tank by low power
1. Field of the Invention wireless means So as to avoid the problems and inherent risks
This invention relates to a fluid level monitor having an that have heretofor been associated with conventional oil tank
ultrasonic transducer that is adapted to accurately detect the level monitors and data transmission techniques.
level of oil or water in a storage tank of the kind that is 10
typically located in the field near an oil or gas well. The SUMMARY OF THE INVENTION
monitor includes an explosion proof casing and wireless
transmission means by which fluid level data is sent to a A wireless fluid level monitor is disclosed having an ultra
remote mobile or stationary data collector or relay. Sonic transducer that is capable of providing an accurate
2. Background Art 15 indication of the level of oil or water that is stored in a
It is desirable to be able to monitor the level of oil (or water) recovery tank of the kind that is typically located within an
that is removed from an oil (or gas) well and stored within a explosive environment near an oil orgas well. The fluid level
recovery tank near the well. Accurate monitoring is required monitor is coupled to an existing fitting at the top of the tank
to reduce the risks of an overflow condition and potential oil such that the ultrasonic transducer is received within the tank
spillage at the tank site which could result in an environmen below the top, and the acoustic axis of the ultrasonic trans
tal and/or safety hazard. One conventional technique to ducer is directed vertically downward towards the fluid to be
accomplish Such oil level monitoring is for a workman to go monitored. The fluid level monitor is surrounded and pro
out in the field and drive from tank-to-tank. The workman tected by a gas tight and explosion proofrated casing. An RF
climbs to the top of each tank, and a string or similar line is transceiver having an antenna is capable of sending data to a
then dropped into the tank from above to measure the oil level. 25 mobile or stationary data collector or relay that is located
The workman manually records the oil levels of the tanks and outside the explosive environment by which to indicate the
then returns to his base of operation. The aforementioned level of oil/water in the tank, the rate at which the tank is being
technique of having to visit the tanks in the field on a one-by filled, and the volume (in barrels) of oil/water in the tank, so
one basis at which to use a string test line and make a manual that the efficiency of the well associated with the tank can be
record of the oil levels is very time consuming, expensive and 30 determined.
not completely accurate. Moreover, the monitoring procedure The wireless fluid level monitor includes a main CPU and
is completed at relatively long intervals, such that a tank a low current power supply which is controlled by the main
approaching full capacity may not be detected intime to avoid CPU and is normally inactive except when tank level readings
an overflow. are to be taken. An internal real time clock is set to enable (i.e.,
Ultrasonic tank level monitoring methods are known. 35 wake up) the main CPU at regular (e.g., one hour) intervals so
However, such ultrasonic methods tend to be inaccurate as to check for an alarm (e.g., tank overflow) condition. A pair
because they fail to take into account the environment within of parallel connected 3.6 volt lithium ion batteries are con
the tank in which the level measurements are to be taken. For nected to an input terminal of the power Supply. An ultrasonic
example, temperature and pressure changes within the tank, transducer is driven by a step-up controllable Voltage regula
Surface ripples, a short measurement range to the Surface of 40 tor of the power Supply. The ultrasonic transducer is mounted
the oil, and hydrocarbon vapors which fill the tank above the below the top of the tank and adapted to operate at a frequency
oil may all give rise to false readings and an indication of of 59 KHZ. Because of the corrosive and hostile environment
more or less oil than is actually present. In addition, conven within which the tank level measurements are to be taken, the
tional ultrasonic monitoring methods are typically limited to ultrasonic transducer is sealed in Teflon and then encased
tanks which are no greater than twelve feet high. Moreover, 45 within a protective (e.g., Delrin) housing. An ultrasonic trans
few ultrasonic tank level monitors are capable of transmitting ceiver is responsive to raw analog incident and reflected sig
data by wireless transmission means. In this regard, the level nals being transmitted by and returned to the ultrasonic trans
data is often transmitted over wire lines which mandates an ducer. The analog signals are conditioned and filtered by the
independent source of power, increases the cost of installation ultrasonic transceiver and supplied to A/D terminals of the
and maintenance, and limits the rate and range at which data 50 main CPU where the signals are digitized and stored in an
can be transmitted. Furthermore, a costly vaportight conduit internal RAM of the CPU. The main CPU computes the
running above the tank is also required to Surround and pro distance between the surface of the oil and the ultrasonic
tect those wires which transmit the oil level data. transducer depending upon the time of flight between the
The environment in which the tank level measurements are incident and reflected transducer signals.
taken is known to be very hostile and corrosive. More par 55 Instead of waiting for its internal clock to wake up the main
ticularly, the environment inside and Surrounding an oil stor CPU on a periodic basis, an optional wake up means is pro
age tank is typically acidic, includes a high concentration of vided to allow tank level measurements to be taken on an
potentially volatile vapors, and is Subject to temperature as-needed basis. In this case, an infrared sensor is located
extremes which often range from as low as -30 degrees C. to behind a sealed transparent panel in the explosion proof cas
as high as +60 degrees C. Workmen who must enter the 60 ing of the fluid level monitor. The infrared sensor is respon
hazardous environment of an oil well and its neighboring sive to a Sudden change in temperature (e.g., such as when a
storage tank to collect or receive oil level data are exposed to technician passes his hand in front of the transparent panel)
personal risk. In this same regard, there is no known ultra for causing the main CPU to wake up and initiate a tank level
Sonic tank level monitoring equipment currently in use that is measurement, the results of which are available on a display
both gas tight and explosion proof so as to ensure the ability 65 that is located behind the transparent panel.
of the monitoring equipment to function properly in Such a The RF transceiver of the wireless fluid level monitor
hostile environment. includes a self-contained CPU that is interfaced with a serial
 US 7,562,570 B2
3 4
I/O terminal of the main CPU. The CPU of the RF transceiver FIGS. 10A and 10B are flow diagrams by which to illus
is awakened on a periodic basis by an internal real time clock trate the steps for monitoring the level of oil/water and deriv
thereof to determine if the transceiver is being selectively ing data which is an accurate representation thereof.
polled for tank level data by the mobile or fixed data collector
or relay. In the event that a polling signal is detected (accord 5 DESCRIPTION OF THE PREFERRED
ing to a unique ID number assigned to the fluid level monitor), EMBODIMENT
the CPU of the RF transceiver will wake up the main CPU and
input an instruction set thereto. Tank level data computed by FIG. 1 of the drawings shows a conventional oil storage
the main CPU is returned to the RF transceiver to be trans tank 1 that is located in the field in the vicinity of an oil well.
mitted from the antenna thereof over a wireless communica 10 While reference will be made herein to an oil storage tank, it
tion path back to the data collector or relay within which the is to be expressly understood that other fluids, such as water,
data is stored for later evaluation or relayed to another loca may also be stored within tank 1. The oil tank 1 is filled via an
tion. If a polling ID signal is not detected by the CPU of the inlet 3 with oil that is pumped from the adjacent oil well. Oil
RF transceiver, then the CPU returns to a sleep (i.e., inactive) is removed from the tank 1 when full via an outlet 5 to be
State. 15 transported by truck to a refinery for processing. The tank 1
In order to permit the oil level readings to be calibrated for would be typically located adjacent a gas well had water been
stored therein instead of oil.
accuracy, a reference rod is affixed to the protective housing
in which the ultrasonic transmitter is encased, so that the In accordance with the present invention, a wireless fluid
reference rod extends downwardly from the top of the tank level monitor 7 is mounted on top of the tank 1 to be respon
towards the surface of the oil to be monitored. The reference sive to the level of oil with which the tank is filled or partially
rod carries one or more (e.g., stainless steel) acoustic reflec filled. As will be explained in greater detail hereinafter, the
tors that are attached (e.g., pinned) at predetermined fixed fluid level monitor 7 includes an ultrasonic transducer having
(e.g., four foot) intervals therealong. Each reflector lies within a vertical acoustic axis that is directed downwardly from
the ultrasonic beam and is adapted to reflect an echo pulse above the oil to be monitored within tank 1. To this end, and
back to the ultrasonic transducer. Depending upon the time of 25 as is best shown in FIG.4, a protective housing 50 around the
ultrasonic transducer includes a set of screw threads 66 to be
flight between the incident pulse and the echo pulse, the main coupled to the outer casing 22 of monitor 7. The protective
CPU of the fluid level monitor calculates the distance of the
reflector from the ultrasonic transmitter and compares this housing 50 also has a set of pipe threads 51 to be mated to an
distance with the known fixed distance. The main CPU will existing threaded fitting 8 located at the top of the oil tank 1.
then make corresponding compensations to the time of flight 30 In this manner, the ultrasonic transducer of monitor 7 will cast
between the incident pulse and the return pulse that is a relatively narrow ultrasonic beam 10 (e.g., across an angle
reflected off the surface of the oil back to the transducer to of approximately 10 degrees) downwardly towards the oil to
account for the environment (e.g., temperature, pressure and be monitored. A narrow beam width is preferred to prevent
hydrocarbon vapors) within the tank, whereby to improve the reflections off the sides of the tank or from objects (e.g.,
accuracy of the data that is transmitted by the fluid level 35 ladders and pipes) commonly located within the tank that
monitor at its antenna. could introduce errors. In this regard, it is preferable that the
ultrasonic transducer (designated 40 in FIG. 3) of monitor 7
BRIEF DESCRIPTION OF THE DRAWINGS be positioned immediately below the inside face of the top of
oil tank 1. However, in the case where the tank has a center
40 fitting for venting purposes, an extension (not shown) may be
FIG. 1 illustrates an oil/water recovery tank with the ultra required to mount the transducer 40 inside the top of the tank.
sonic oil/water level monitor of the present invention coupled As will also be explained in greater detail, the wireless fluid
to the top of the tank for measuring the level of oil/water level monitor 7 herein disclosed includes an antenna 12 by
stored therewithin and for transmitting data indicative thereof which to transmit data over a wireless communication path to
over a wireless transmission path; 45 a distant location concerning the level of oil within tank 1 so
FIG. 2 illustrates a series of oil/water recovery tanks having as to provide a warning of a possible overflow condition, the
respective ultrasonic oil/water level monitors for transmitting rate at which the tank is filled with oil, and the volume (in
tank level data by wireless means to any one of a plurality of barrels) of oil within the tank 1 so that an indication will be
mobile or stationary data collectors or relays; readily available to measure the oil producing efficiency of
FIG.3 is a block diagram showing a preferred embodiment 50 the associated oil well. What is more, by virtue of the fluid
of the ultrasonic oil/water level monitor of the present inven level monitor 7 of this invention, the data being transmitted at
tion; antenna 12 will have a high degree of accuracy relative to the
FIG. 4 shows a protective housing to Surround and encase data that is supplied by conventional fluid level monitors.
an ultrasonic transducer of the ultrasonic oil/water level That is, hydrocarbon vapors above the oil and/or changes in
monitor of FIG. 3; 55 temperature and pressure inside the tank can result in the
FIG.5 shows the ultrasonic transducer to be encased in the transmission of erroneous data (e.g., such as where a smaller
protective housing of FIG. 4 and to be aligned with respect to or greater volume of oil is indicated than that which is actually
an oil/water tank in the manner illustrated in FIG. 3. stored within the tank).
In order to adjust the readings of the fluid level monitor 7
FIG. 6 is illustrative of the analog signal transmitted by and 60 for accuracy, a reference rod or tube 14 extends downwardly
returned to the ultrasonic transducer and including incident, from the monitor through the interior of the tank 1. The
reflected and calibration pulses; reference rod 14 has one or a series of acoustic reflectors 16
FIGS. 7 and 8 show a reference rod having one or more uniformly spaced (e.g., at four foot intervals) therealong.
acoustic reflectors by which to calibrate and improve the Details of the reference rod 14 will be described when refer
accuracy of the oil/water level monitor; 65 ring to FIGS. 7 and 8.
FIG. 9 is a cross section of an acoustic reflector connected FIG. 2 of the drawings illustrates a plurality of storage
to the reference rod of FIGS. 7 and 8; and tanks located in the field with each tank having a wireless
 US 7,562,570 B2
5 6
fluid level monitor 7 mounted at the top of the tank. In this dog timer 32 is an independent low current, resetable (to one
case, one of the tanks 1-1 contains oil, a second tank 1-2 hour) counter which tracks CPU activity and is conditioned to
contains water and yet another tank 1-3 functions as an over reset the CPU24 in the event that the CPU is not awakened by
flow tank in the event that oil or water must be removed from its own internal clock 30. Once awakened, the CPU 24 will
one of the storage tanks 1-1 or 1-2 should the fluid level 5 check its instruction set, activate the power Supply 26 so that
monitor 7 thereof detect an imminent overflow condition and voltage is supplied to transducer 40, and switch on the A/D
a potential environmentally unfriendly oil spill. However, the converter 34 which is connected to output terminals of the
contents of the tanks illustrated in FIG. 2 is not to be consid ultrasonic transceiver 28 by which analog signals indicative
ered a limitation of this invention. offluid level that are produced by the ultrasonic transducer 40
In the case of FIG. 2, any one or all of the storage tanks 1-1, 10 are supplied to A/D converter 34 to be digitized for analysis
1-2 or 1-3 may communicate over a wireless data communi by CPU 24.
cation path between antenna 12 and the antenna of a remote The main CPU 24 is periodically awakened by its internal
mobile or stationary data collector or relay. Each remote data clock 30 to determine if a potential overflow condition exists
collector includes suitable memory in which data is stored for within the tank and whether an alarm signal should be gen
later evaluation and may be a hand-held device 18-1 that is 15 erated. That is, if the oil level or the rate of fill within the tank
carried by a field worker walking near the storage tanks, or a exceeds predetermined and preprogrammed limits, the CPU
vehicle mounted device 18-2 transported by a motor vehicle 24 will initiate an alarm signal. The alarm signal is transmit
driving past the storage tanks, or an aircraft mounted device ted with the particular ID of the fluid level monitor 7 to the
18-3 that is flown over the storage tanks. A fixed (e.g., pole fixed data relay 18-4 of FIG. 2. The alarm signal is then sent
mounted) data relay 18-4 is also contemplated to be accessed 20 from data relay 18-4 to a remote station until an acknowl
by cellphone dial-in, satellite, or the like. The data from relay edgement is received. In the case where a fixed data relay 18-4
18-4 can be sent to other locations by modem, wide area is not located in the vicinity of the fluid level monitor 7 or the
networking, or a customer provided data interface. Such a main CPU 24 is only programmed to communicate with one
fixed data relay 18-4 will be suitably spaced from the tanks of the walk-by, drive-by, or fly-by data collectors 18-1, 18-2
1-1 ... 1-3 so as to lie outside the explosive environment 25 and 18-3 of FIG. 2, then the alarm condition and the time of
which surrounds the tanks. Reference may be made to my the event are stored in the CPU 24 until the fluid level monitor
U.S. Pat. No. 6,967,589 for details concerning the fixed data 7 is selectively interrogated in the manner previously
relay like that described herein. described.
Each of the fluid level monitors 7 atop the respective stor The main CPU 24 is provided with an optional wake up
age tanks 1-1 . . . 1-3 is provided with a unique digitally 30 means to be used in substitution of its internal real time clock
encoded identification number. The data collectors or relay 30. As previously described, internal clock 30 enables the
18-1 ... 18-4 selectively interrogate the monitors 7 of the CPU24 to wake up at regular predetermined time intervals to
tanks so as to gain access to the data collected by each moni check for potential overflow conditions. The optional wake
tor, one at a time, depending upon the particular ID number up means allows technicians to enable the CPU 24 to wake up
being transmitted. 35 at any time when it is desirable to take a fluid level reading on
Turning now to FIG. 3 of the drawings, details of the an as-needed basis. To accomplish the foregoing, the gas
wireless fluid level monitor 7 shown in FIGS. 1 and 2 are now tight explosion-proof casing 22 is provided with a sealed
provided. In order to enable the monitor 7 to survive in the transparent (e.g., thick Pyrex) front panel 35 behind which is
harsh gas and oil well environment in which the data will be located an infrared sensor 36. The sensor 36 is responsive to
collected and transmitted, monitor 7 is advantageously Sur- 40 a Sudden temperature change Such as that which will occur
rounded by a gas tight and explosion proof rated casing 22 when the technician passes his uncovered hand in front of the
such as a Series XIHM casing manufactured by Adelet. The transparent front panel 35. The sensor 36 is connected to the
monitor 7 is controlled by a main CPU 24. By way of CPU 24 to initiate a contemporaneous fluid level reading, the
example, the main CPU 24 is a standard 16-bit microproces results of which are displayed on a liquid crystal or similar
sor with programmable flash memory, internal RAM, a multi- 45 display 38 located behind the transparent front panel 35.
port analog-to-digital (A/D) converter, and an internal oscil The ultrasonic transducer 40 has an acoustic axis 41 which
lator, such as that manufactured by Texas Instruments under extends vertically downward from the exterior of the monitor
Part No. MSP43OF. casing 22 at the top of the oil tank (designated 1 in FIG. 1)
The power supply 26 for monitor 7 is controlled by the towards the tank bottom. A suitable ultrasonic transducer for
main CPU 24. Power supply 26 is a low current (for safety), 50 use in taking fluid level readings is that which includes a
low power device which is normally in an inactive (i.e., sleep) piezoelectric transducer element, a receiver pre-amp, and a
mode except when tank level readings are to be taken. A DC drive oscillator. The transducer 40 preferably operates at a
input terminal of the power Supply 26 is connected through an frequency of 59 KHZ. Because it will be exposed to the
on-off switch to a pair of 3.6 volt lithium ion battery cells 27 corrosive environment of the oil tank, the transducer 40 is
that are arranged in electrical parallel to provide 36 amp hour 55 preferably sealed in Teflon and surrounded by a non-conduc
capacity. The ultrasonic transducer 40 is powered by a step-up tive protective housing.
controllable voltage regulator of the power supply 26. The Referring briefly in this regard to FIGS. 4 and 5 of the
step-up Voltage which is provided from an output terminal of drawings, there is shown in FIG. 4 the protective housing 50
the power supply 26 to the transducer 40 is controlled by the in which the ultrasonic transducer 40 will be received and
CPU 24 and preferably lies in a range of 4 to 12 volts DC 60 encased so as to be protected from the corrosive environment
which, with the pulse width, sets the output power of the of the oil tank 1. The housing 50 is machined with a (e.g.,
ultrasonic transducer. The pulse width is also controlled by three inch) pipe thread 51 which is to be mated to a corre
CPU 24. spondingly threaded fitting (designated 8 in FIG. 1) at the top
An internal real time clock 30 with a 38.4 KHZ crystal 31 of the oil tank shown in FIG.1. A threaded coupler 66 extends
will periodically enable (i.e., wake up) the main CPU 24 at 65 from the housing 50 to be mated to the gas-tight, explosion
certain predetermined (e.g., one hour) intervals. When the proof casing 22 that surrounds the fluid level monitor 7. By
CPU24 is enabled, a watch dog timer 32 is reset. The watch way of example, the protective housing 50 is manufactured
 US 7,562,570 B2
7 8
from a non-metallic acetal resin material known commer identical to the main CPU 24 of monitor 7. Once it is awak
cially as Delrin that is available from Dupont Corporation. ened, the main CPU 24 causes the ultrasonic transducer 40 to
A cylindrical cavity 52 is formed at the front of the housing take an oil level reading within the tank.
50 in which to slidably receive the ultrasonic transducer (des An analog representation of the oil level readings taken by
ignated 40 in FIGS. 3 and 5). A pair of (e.g., Viton) O-rings 5 transducer 40 is supplied to the ultrasonic transceiver 28 to be
(only one of which 54 being shown) extend around the cavity applied to the A/D converter 34 of the main CPU 24. Digital
52 to seal the transducer 40 therewithin. A longitudinally data concerning the oil level readings is sent from the main
extending channel 56 communicates with cavity 52 to enable CPU 24 to the CPU 44 of RF transceiver 42 to be transmitted
a set of five electrical wires to run from the transducer to a over a wireless communication path from antenna 12 back to
connector 58. In the assembled relationship of FIG. 3, the 10 the remote data collector or relay to be retransmitted or
transducer 40 is coupled to the ultrasonic transceiver 28 of the relayed for evaluation. In the case where the CPU 44 of RF
fluid level monitor 7 by way of connector 58. The wire set transceiver 42 does not detect a polling ID signal, it will return
running through channel 56 to connector 58 is surrounded by to its inactive state and the main CPU 24 remains asleep.
a cable sleeve 60, and the cable sleeve 60 is embedded within The RF transceiver 42 is preferably a commercially avail
channel 56 that is backfilled with a suitable encapsulant 62, 15 able Xemics RF integrated circuit which utilizes a 902/925
Such as epoxy, or the like. MHz. ISM band. Modulation in this case will be broadband
FIG. 5 of the drawings illustrates details of the 5-wire (500 KHz) FSK. Power output is limited to 16 mw to avoida
ultrasonic transducer 40 that was previously described while potentially explosive incident. The antenna 12 of wireless
referring to FIG. 3. The transducer 40 is sized and (e.g., monitor 7 is preferably a 5/8 wave vertical antenna with an
cylindrically) shaped so as to be slidably received within the SMA type connector. The gain of antenna 12 is +5.5 db. As
cylindrical cavity 52 formed in the protective housing 50 of with the case of the ultrasonic transducer 40, the antenna 12 is
FIG. 4. By way of example, the transducer 40 is approxi sealed in a non-conductive protective covering manufactured
mately 2 inches long with a diameter of approximately 2 from Teflon.
inches, an operating temperature range of -10 degrees C. to A variable gain amplifier (i.e., bandpass filter) 28a of the
+70 degrees C., an RX gain of 30 db and a Tx pulse power of 25 ultrasonic transceiver 28 is connected between an out termi
4 volts to 15 volts DC (at 50 ma max peak). A pair of circum nal of the ultrasonic transducer 40 and the A/D converter 34 of
ferentially extending grooves 64 surround the Teflon covered the main CPU 24. Amplifier 28a receives raw analog signals
transducer 40 in which to receive the (Viton) O-rings 54 that from the ultrasonic transducer 40 which are indicative of the
are carried by the transducer housing 50 of FIG. 4 so that the time of flight between an incident acoustic signal transmitted
transducer will be held, aligned and sealed within cavity 52 30 by the transducertowards the oil in the tank and a return signal
and the acoustic axis 41 thereof will be directed vertically reflected to the transmitter from the surface of the oil. The raw
downward from the top of the tank towards the fluid to be analog signals supplied by the ultrasonic transducer 40 are
measured. conditioned and filtered by the amplifier (bandpass filter) 28a
Returning now to the details of the fluid level monitor 7 to be provided to the A/D converter 34 of the main CPU where
shown in FIG. 3, by programming the main CPU 24 with the 35 the analog data is digitized and analyzed. By programming
dimensions of the oil tank, information can be gathered the main CPU 24 with the dimensions of the tank in which the
regarding the level of oil within the tank, the volume of the oil measurement is to be taken, the level of the oil within the tank
within the tank, the rate at which the tank is being filled with (and other useful information as earlier described) can be
oil, whether the tank is approaching full capacity and is, calculated depending upon the time of flight between the
therefore, in need of being partially emptied to avoid spillage 40 incident and return signals. The digitized tank level data is
(whereby the aforementioned alarm signal may be gener then Stored within the internal RAM of CPU 24. In this
ated), and, correspondingly, the production efficiency of the manner, the tank level measurement can be repeated and
associated oil well. The gathered information is Supplied as a compared with previously collected measurement data that is
stream of digital data from a serial 110 terminal of the main stored in the internal RAM so as to ensure the consistency of
CPU24 to an RF transceiver 42 to be broadcast via antenna 12 45 the measurements and the reliability of the data to be ulti
over the aforementioned wireless communication path to one mately transmitted from the antenna 12 of RF transceiver 42.
of the data collectors or data relay illustrated in FIG. 2. An optional external RAM or flash memory 46 may be con
The RF transceiver 42 is a low power ISM transceiver using nected to the main CPU 24 in which the digitized tank level
DSSS modulation for sending and receiving data at 38.4 data can be stored for later recall and evaluation.
Kbits. The RF transceiver 42 has a self-contained CPU 44 50 The ultrasonic transducer 40 is pulse width controlled
which is independent of the main CPU 24 and is periodically through a Txpulse inverter 29 connected to a Txpulse output
enabled from a sleep (i.e., inactive) state by its own internal terminal of the main CPU 24. The ultrasonic transducer 40
real time clock to determine whether receiver 42 is being responds to the CPU by providing its 59 KHZ transmitted
selectively accessed (i.e., polled) for data by one of the remote output at the selected power. The variable gain amplifier 28a
data collectors or data relay 18-1 ... 18-4 shown in FIG. 2. 55 has a gain of X 4.5 and a high cutoff of approximately 100
That is, and as was previously disclosed when referring to KHZ. The gain of the amplifier 28a is controlled by the TX
FIG. 2, each fluid level monitor 7 in a system of monitors at pulse output of the main CPU 24 and a near gain control 28b
respective oil tanks 1-1 ... 1-3 may be assigned a particular ID of ultrasonic transceiver 28. The gain is initially lowered to X
number. 1 for approximately 2 ms and then ramped up to X 4.5 in three
If the monitor 7 receives appropriate ID and command 60 ms by control 28b. This action prevents over-driving the
signals transmitted to its antenna 12 from any one of the amplifier 28a and missing short range ultrasonic returns in the
walk-by, drive-by, fly-by, or fixed data collectors or data relay range of 12 inches to 24 inches where the level of oil is close
(designated 18-1 ... 18-4 in FIG. 2) that are located outside to the top of the tank in which the fluid level monitor 7 is
the explosive environment of the tank, the CPU 44 of trans mounted.
ceiver 42 will wake up the main CPU 24 of monitor 7 and 65 The ultrasonic transceiver 28 also includes a temperature
input the commands thereto via the serial I/O terminal. By amplifier 28c that is connected between the ultrasonic trans
way of example, the CPU 44 of RF transceiver 42 may be ducer 40 and the A/D converter 34 of the main CPU. Tem
 US 7,562,570 B2
10
perature amplifier 28c generates a DC voltage that is indica Each reflector 16 that is carried by the reference rod 14 is
tive of the temperature at the face of transducer 40 at the top manufactured from a material (e.g., stainless steel) that, when
of the tank in which a level measurement is to be taken. The located within the narrow ultrasonic beam (designated 10 in
temperature information is read by CPU 24 and used during FIG. 1), is adapted to reflect an echo signal back to the
its calculation of oil level. That is, by calibrating the DC bias ultrasonic transducer within the protective housing 50. This
Voltage on transducer 40, a linear temperature value is readby echo signal is represented by the echo pulse 74 as part of the
the CPU 24 and used to adjust the time of flight of the acoustic analog signal 70 of FIG. 6. The single echo pulse 74 shown in
signal transmitted and received by the transducer. FIG. 6 is indicative of a relatively short reference rod having
FIG. 6 of the drawings illustrates an analog signal 70 that is a single acoustic reflector. Each reflector 16 is preferably a
produced by the ultrasonic transducer 40 and supplied to the 10 cylindrical weight that is sized so as to prevent any loss of the
A/D converter 34 of the main CPU 24 after the signal is analog signal that is reflected off the surface of the oil and
conditioned and filtered by the amplifier/filter 28a of the returned to the ultrasonic transducer 40. By way of example,
ultrasonic transceiver 28 offluid monitor 7 of FIG.3. The data the reflector 16 has a length of 2 /2 inches and a diameter of
collected by the main CPU24 is the analog signal 70 bit sliced 0.75 inches. As is best shown in FIG. 9 of the drawings, each
by the A/D converter 34 at a 16 usecond sample rate. The A/D 15 reflector 16 is connected to opposing lengths of the reference
converter 34 is preferably a 12 bit device such that 3.2K bytes rod 14 by means of stainless steel roll pins 83 or any other
suitable fastener.
of data are stored in the internal CPU RAM for analysis for When it is awakened to take a fluid level measurement, the
each level measurement. The analog signal includes an inci main CPU 24 of the fluid level monitor 7 of FIG.3 decodes the
dent pulse 72 that is indicative of the acoustic signal trans reference readings (i.e., the echo pulse or pulses 76 contained
mitted by ultrasonic transducer 40 towards the surface of the in the analog signal 70 of FIG. 6) and makes corrections for
oil within the tank and a reflected pulse 74 that is returned to errors in the oil level measurement introduced by the tank
the transducer 40 from the surface of the oil. The elapsed time environment. More particularly, the main CPU 24 is initially
of flight (designated TOF) between the peaks of the incident programmed with the height and diameter of the tank and the
and reflected pulses 72 and 74 represents the time of transit of 25 number of and distance between the reflectors 16 that are
the acoustic signal 70 from its transmission by the ultrasonic connected to the reference rod 14. As previously described,
transducer 40 to its receipt by transducer 40 after reflection the reflector 16 of the reference rod 14 shown in FIGS. 7 and
off the surface of the oil. Since the time of flight represents a 8 is known to be located a precise distance (e.g., four feet)
round trip from and to the ultrasonic transducer 40, the main below the face of the ultrasonic transducer that is encased by
CPU 24 divides the elapsed time calculation in half and uses 30 housing 50. The CPU 24 calculates the measured distance of
the resulting time to calculate the distance form the face of the reflector below the transducer based upon (one half) the
transducer 40 to the surface of the oil.
The analog signal 70 of FIG. 6 also includes an echo pulse elapsed round trip time between the incident pulse 72 of the
analog signal 70 generated by the ultrasonic transducer and
76 between the incident and reflected pulses 72 and 74. For the echo pulse 76 that is reflected off the reflector 16 and
purposes of convenience, the analog signal 70 is shown with 35 returned to the transducer 40.
a single echo pulse 76. However, as will soon be explained, Depending upon whether the measured distance calculated
depending upon the length of the reference rod (designated 14 by CPU24 is less than or greater than the true distance of four
in FIG. 1) and the number of reflectors 16 carried thereby, the feet and the amount of such difference, the CPU 24 will make
analog signal 70 of FIG. 6 may include two or more echo corresponding compensations to the time of flight (TOF)
pulses. 40 between the incident pulse 72 transmitted by the transducer
Referring in this regard to FIGS. 7 and 8 of the drawings, 40 and the reflected pulse 74 returned to the transducer from
there is shown the reference rod 14 according to a preferred the surface of the oil. At the same time, the CPU 24 will use
embodiment affixed to the outside of the protective housing the reflected echo pulse 74 to adjust the power being supplied
50 within which the ultrasonic transducer 40 of FIG. 5 is from the power supply 26 of the fluid level monitor 7 of FIG.
encased. The reference rod 14 is located within an axially 45 3 to the ultrasonic transducer 40.
extending slot (designated 80 in FIG. 8) and affixed in place In the case where more than a single reflector 16 is con
therein by means of screws 82, or the like. The reference rod nected to the reference rod 14, a calibration table may be
14 projects from housing 50 past the face of the transducer so compiled as each Successive reflector is covered by the rising
as to extend downwardly from the top of the tank towards the oil. This table may be updated continuously to adjust for
surface of the oil to be monitored. As was previously indi 50 changing tank conditions and fluid levels.
cated, the reference rod 14 advantageously permits the oil Turning now to FIG. 10A of the drawings, there is shown a
level readings to be calibrated for accuracy by taking into flow diagram to illustrate the steps by which the fluid level
account environmental conditions (e.g., vapors above the oil, monitor 7 shown in FIG.3 takes fluid level measurements and
changes in temperature, pressure, etc.) within the tank. transmits digital data to provide an accurate indication
The reference rod 14 has reference marks (i.e., acoustic 55 thereof. Initially (101), the main CPU 24 is awakened. This
reflectors 16) that are located at predeterminedfixed distances may occur when a particular ID polling signal is received at
below the face of the ultrasonic transducer. By way of the antenna 12 of RF transceiver 42 to request access to the
example, the reflectors 16 are located at uniform four foot data compiled by monitor 7. The ping count (102) is set to 0
intervals along the reference rod 14. The reference rod 14 is in the main CPU 24. In the present example, three different
preferably a 4-3/8 inch diameter tube that is manufactured 60 fluid level measurements will be taken by the ultrasonic trans
from Teflon or any other material that is capable of withstand ducer 41, and, following analysis by the main CPU 24, digital
ing the harsh (gaseous and acidic) conditions within the tank. representations thereof are stored in the internal CPU RAM
Reference rod 14 has different lengths having different num for comparison. The ping count is updated for each Successive
bers of reflectors for use in tanks of different height. A short measurement. For purposes of reliability, at least two of the
tank may require a reference rod with only a single length and 65 fluid level measurements must be within a predetermined
a single reflector. Taller tanks will typically require two or tolerance before output data is supplied by CPU 24 at the I/O
more lengths and a corresponding number of reflectors. terminal thereof for transmission via antenna 12.
 US 7,562,570 B2
11 12
The temperature is measured (103) at the face of the ultra tor returns an echo pulse (designated 76 in FIG. 6) to the
Sonic transducer 40, and an indication thereof is provided to transducer 40. Accordingly, the first step (125) is to determine
the main CPU 24 by way of the temperature amplifier 28c of if an echo pulse has been returned from any reflector that is
the ultrasonic transceiver 28. The Tx pulse width and the carried by the reference rod 14 which lies eight feet from the
voltage supplied to the ultrasonic transducer are set (104) by transducer 40. In the example of FIG. 6, only a single reflector
CPU 24 to control the output power of transducer 40 via TX 16 is located four feet from the transducer.
pulse inverter 29 so that the analog signal (designated 70 in Following a determination (126) that there is no reflector at
FIG. 6) can be detected and analyzed. The time of flight eight feet (or more) along the reference rod 14 and, therefore,
(TOF) is then calculated (105) between the incident and no echo pulse has been returned therefrom, a determination is
return pulses (designated 72 and 74 in FIG. 6) of the analog 10 made (127) whether a reflector 16 is located on reference rod
signal 70 with compensation for the temperature provided via 14 four feet from the ultrasonic transducer. In the event that it
amplifier 28c. The return pulse 74 of the analog signal 70 is is determined (128) that a reflector is located four feet along
classified (106) as being either too high or too low. The return the reference rod 14, or if it was previously determined (126)
pulse 74 should preferably have a height corresponding to that there was a reflector at the eight foot reference mark, the
approximately 1 volt so as not to overdrive the amplifier 28a 15 time of flight is computed by the main CPU 24 between the
of ultrasonic transceiver 28. If the voltage associated with the incident pulse (72 in FIG. 6) generated by the ultrasonic
return pulse 74 is too low (107), then the Txpulse width from transducer 40 and the echo pulse 76 returned from each
main CPU 24 and the voltage provided to the ultrasonic reflector 16. The time of flight is converted into distance and
transducer 40 from power supply 26 are increased (108). compared (129, 130) with the known four and eight foot
However, if the Voltage associated with the return pulse 74 is distances at which the reflectors are located along the refer
otherwise too high (109), then the Tx pulse width and the ence rod 14. Depending upon whether the computed time of
output voltage from power supply 26 are decreased (110). flight is greater or less than four (or eight) feet, the main CPU
The ping count maintained by CPU 24 is then increased 24 makes a corresponding adjustment (i.e., correction 131) to
(111) from 0 to 1 or from 1 to 2. A ping count of 2 indicates the time of flight (TOF) between the incident and return
that three fluid level measurements have been taken (i.e., at 25 pulses (72 and 74 in FIG. 6) which is indicative of the time
ping counts=0, 1 and 2). Therefore, if the ping count is only 0 required for an acoustic signal to be transmitted from trans
(112), the process returns to step 104 so that additional fluid ducer 40 to the surface of the fluid within the tank and
level measurements can be taken. If the ping count has oth reflected off the surface and returned to the transducer. The
erwise reached 1 (112), then the CPU 24 makes a comparison corrected time of flight is converted (132) into an accurate
(113) of the fluid level measurement data stored in the internal 30 distance between the ultrasonic transducer 40 and the level of
CPU RAM during the first and second measurements (i.e., the fluid to be measured within the tank.
ping counts=0 and 1). If the comparison is out of a predeter The calibration method is now ended (133) and, as previ
mined tolerance, the data is deemed unreliable and the ously disclosed, the main CPU 24 sends reliable fluid level
method returns to step 104. If the comparison is within toler data to the RF transceiver 42 from which such data is trans
ance, the first and second fluid level measurement data is 35 mitted by antenna 12 over a wireless communication path. It
preserved (114). may be appreciated that the data can be automatically trans
In the case where the ping count has reached 2 (115) mitted in response to a particular ID polling signal at high
indicating the third of the three fluid level measurements, the speed and over long distances without the use of wires or
CPU 24 makes a comparison (116) of the fluid level measure requiring the presence of a field worker to make manual
ment data during the first and third measurements. If this 40 measurements. Moreover, the accuracy of the data is greatly
comparison is not out of predetermined tolerance, the first and enhanced relative to conventional fluid level measurement
third fluid level measurement data is preserved (117). Next, techniques.
the CPU 24 makes a comparison (118) of the fluid level Although the fluid level monitor herein disclosed has par
measurement data during the second and third measurements. ticular application for detecting the level of oil or water in a
If this comparison is not out of predetermined tolerance, then 45 storage tank, it should be recognized that the monitor can
the second and third fluid level measurement data is preserved effectively be used to detect the levels of different fluids
(119). including, but not limited to, other petroleum products,
It may be found that all of the comparisons between the first chemicals, hazardous liquids, liquid waste, etc.
and second, first and third, and second and third fluid level The invention claimed is:
measurement data are out of tolerance. Such that none of the 50 1. An ultrasonic monitor to measure the level of a fluid in a
fluid level information collected by the ultrasonic transducer tank and comprising:
40 and Stored within the internal CPU RAM can be relied an ultrasonic transducer adapted to generate an incident
upon as accurate. In this case, an error (i.e., miss) indication acoustic signal towards the surface of the fluid within the
is generated (120) and the method is ended (121) until a new tank and to receive a return signal reflected off the sur
set of three fluid level readings are taken, stored and com 55 face of the fluid;
pared in the manner described above. However, where at least a main central processing unit (CPU) being responsive to
two of the three fluid level readings are within tolerance the incident and return signals generated by and
relative to one another, then the corresponding data (114,117. reflected to the ultrasonic transducer for determining the
119) is used (122) to account for the hostile environment elapsed time of flight therebetween and calculating the
within the fluid tank which is known to introduce errors into 60 distance from the surface of the fluid to the ultrasonic
the time of flight computations made by the main CPU 24. transducer depending upon said elapsed time of flight;
Referring in this regard to FIG.10A and to the beginning of means to adjust the elapsed time of flight determined by the
the fluid level calibration (124), it should be remembered that main CPU to compensate for errors introduced by the
the reference rod (designated 14 in FIGS. 7 and 8) carries one environment within the tank, whereby to maximize the
or more acoustic reflectors 16 at predetermined fixed (e.g., 65 accuracy of the distance calculated by the main CPU:
four foot) intervals therealong so as to lie within the ultrasonic an RF transceiver having an antenna and being interfaced
beam generated by the ultrasonic transducer 40. Each reflec with said main CPU for receiving data therefrom corre
 US 7,562,570 B2
13 14
sponding to the distance calculated by said main CPU, towards the surface of the fluid within the tank so that a
the antenna of said RF transceiver transmitting said dis potential fluid overflow condition within the tank is detected
tance data over a wireless communication path, said RF on a regular basis.
transceiver including a transceiver CPU responsive to a 8. The ultrasonic monitor recited in claim 1, further com
particular ID polling signal transmitted to the antenna of 5 prising a power Supply interfaced with and controlled by said
said RF transceiver when it is desirable to access the data main CPU, said power Supply including a step-up regulator
corresponding to the distance calculated by said main connected to control the output power of said ultrasonic trans
CPU, said transceiver CPU supplying a wake-up signal ducer.
to said main CPU for causing said ultrasonic transducer 9. The ultrasonic monitor recited in claim 8, further com
to generate said incident acoustic signal towards the 10
prising battery means connected to said power Supply for
surface of the fluid within the tank and the resulting data Supplying a DC input voltage thereto.
which is indicative of the distance calculated by the main 10. The ultrasonic monitor recited in claim 1, wherein said
CPU to be supplied to said transceiver CPU for trans main CPU includes an internal memory for storing there
mission by said antenna; within a plurality of Successive distances calculated by said
an infrared sensor interfaced with said main CPU: 15
main CPU, said main CPU comparing the plurality of dis
a gas-tight, explosion-proof casing enclosing at least some tances stored in said internal memory and identifying a par
of each of said ultrasonic transducer, said main CPU, ticular reliable distance calculation depending upon the simi
said RE transceiver, and said infrared sensor, and larities to one another of said distance calculations stored
a transparent panel located in said gas-tight, explosion within said internal memory.
proof casing, said infrared sensor positioned behind said
transparent panel and responsive to a change in infrared 11. The ultrasonic monitor recited in claim 1, further com
energy applied through said transparent panel for Sup prising an ultrasonic transceiver connected to receive an ana
plying a corresponding wake-up signal to the main CPU, log representation of the incident and return signals generated
said main CPU being responsive to said wake-up signal by and reflected to said ultrasonic transducer, said main CPU
for causing said ultrasonic transducer to generate said 25 having an analog-to-digital converter connected to said ultra
incident acoustic signal towards the Surface of the fluid Sonic transceiver to receive said analog representation there
within the tank. from in a condition to be digitized, whereby to enable said
2. The ultrasonic monitor recited in claim 1, wherein the main CPU to determine the elapsed time of flight between
means to adjust the elapsed time of flight includes at least said incident and reflected signals and thereby calculate the
ultrasonic reflector located within the tank a known distance 30 distance from the surface of the liquid within the tank to said
ultrasonic transducer.
from the ultrasonic transducer so as to lie within the path of
the incident acoustic signal and reflect an echo signal to said 12. The ultrasonic transducer monitor recited in claim 11,
ultrasonic transducer, said main CPU being responsive to said wherein said ultrasonic transceiver includes a variable gain
echo signal to determine the elapsed time of flight between amplifier connected between said ultrasonic transducer and
said incident and said echo signals for computing the distance 35 the analog-to-digital converter of said main CPU, the analog
between said ultrasonic transducer and said reflector and representation of said incident and return signals being fil
comparing the computed distance with the known distance. tered and applied to said analog-to-digital converterby way of
3. The ultrasonic monitor recited in claim 2, wherein the said variable gain amplifier.
means to adjust the elapsed time of flight also includes a 13. The ultrasonic monitor recited in claim 11, wherein
reference rod extending into the tank from said ultrasonic 40 said ultrasonic transceiver includes a temperature amplifier
transducer, said at least one ultrasonic reflector connected to connected between said ultrasonic transducer and the analog
said reference rod at the said known distance from said ultra to-digital converter of said main CPU, an indication of the
Sonic transducer. temperature within the tank at said ultrasonic transducer
4. The ultrasonic monitor recited in claim 3, wherein said being applied to said analog-to-digital converter by way of
ultrasonic transducer is surrounded by a protective housing, 45 said temperature amplifier.
said reference rod connected to said protective housing and 14. The ultrasonic monitor recited in claim 1, further com
extending therefrom towards the surface of the fluid to be prising a pulse inverter connected between a pulse output of
measured. the main CPU and said ultrasonic transducer, the width of
5. The ultrasonic monitor recited in claim 1, wherein said pulses Supplied from said pulse output to said ultrasonic
ultrasonic transducer is coupled to the top of the tank and 50 transducer by way of said pulse inverter controlling the output
adapted to generate a narrow ultrasonic beam downwardly power of said ultrasonic transducer.
from the top of the tank towards the surface of the fluid to be 15. An ultrasonic monitor to measure the level of a fluid in
measured, said narrow ultrasonic beam making an angle of a tank having an existing threaded fitting at the top thereof,
approximately 10 degrees. said ultrasonic monitor comprising:
6. The ultrasonic monitor recited in claim 1, further com 55
prising a display located behind the transparent panel of said an ultrasonic transducer adapted to generate an incident
gas-tight, explosion-proof casing and interfaced with said acoustic signal towards the surface of the fluid within the
main CPU, said display providing a visual indication of the tank and to receive a return signal reflected off the sur
distance from the surface of the liquid within the tank to said face of the fluid;
ultrasonic transducer calculated by said main CPU in 60 a central processing unit (CPU) being responsive to the
response to the infrared energy signal applied to said infrared incident and return signals generated by and reflected to
SSO. the ultrasonic transducer for determining the elapsed
7. The ultrasonic monitor recited in claim 1, wherein said time of flight therebetween and calculating the distance
main CPU includes an internal clock that is set to generate from the surface of the liquid to the ultrasonic transducer
wake-up signals at predetermined time intervals, said main 65 depending upon said elapsed time of flight;
CPU responsive to said wake-up signals for causing said an RF transceiver having an antenna and being interfaced
ultrasonic transducer to generate said incident acoustic signal with said CPU for receiving data therefrom correspond
 US 7,562,570 B2
15 16
ing to the distance calculated by said CPU, said antenna a pulse inverter connected between a pulse output of the
transmitting said distance data over a wireless commu CPU and said ultrasonic transducer, the width of pulses
nication path; and Supplied from said pulse output to said ultrasonic trans
a gas-tight casing enclosing at least some of said ultrasonic ducerby way of said pulse inverter controlling the output
monitor, power of said ultrasonic transducer.
wherein said ultrasonic transducer is encased within a pro 20. The ultrasonic monitor recited in claim 19, wherein
tective non-metallic housing, said protective housing said CPU includes an internal clock that is set to generate
having a set of pipe threads to be coupled to the existing wake-up signals at predetermined time intervals, said CPU
threaded fitting at the top of the tank and a threaded being responsive to said wake-up signals for causing said
couplerto be mated to said gas tight casing Such that said 10 ultrasonic transducer to generate said incident acoustic signal
ultrasonic transducer has an acoustic axis directed towards the surface of the fluid within the tank so that a
downwardly towards the surface of the fluid to be mea potential fluid overflow condition within the tank is detected
Sured. on a regular basis.
16. The ultrasonic monitor recited in claim 15, further 21. The ultrasonic monitor recited in claim 19, further
comprising means to adjust the elapsed time of flight deter 15 comprising a power Supply interfaced with and controlled by
mined by said CPU to compensate for errors introduced by said CPU, said power Supply including a step-up regulator
the environment within said tank, whereby to maximize the connected to also control the output power of said ultrasonic
accuracy of the distance calculated by said CPU. transducer.
17. The ultrasonic monitor recited in claim 15, wherein the 22. The ultrasonic monitor recited in claim 19, further
tank in which the fluid level is measured is covered by a top, comprising a battery connected to said power Supply for
said ultrasonic transducer being coupled to said tank below Supplying a DC input voltage thereto.
the top thereof so as to generate a narrow ultrasonic beam 23. The ultrasonic monitor recited in claim 22, further
downwardly from the top towards the surface of the fluid to be comprising a gas-tight, explosion-proof casing coupled to the
measured, said ultrasonic transducer operating at a frequency tank and enclosing at lest Some of said ultrasonic transducer,
of approximately 59 KHZ. 25 said CPU, said RF transceiver, and said battery.
18. The ultrasonic monitor recited in claim 15, further 24. The ultrasonic monitor recited in claim 19, wherein the
comprising a reference rod affixed to and extending down tank in which the fluid level is measured is covered by a top,
wardly from the protective housing of said ultrasonic trans said ultrasonic transducer coupled to said tank below the top
ducer towards the surface of the fluid to be measured, and a thereof so as to generate a narrow ultrasonic beam of approxi
plurality of acoustic reflectors spaced from one another along 30 mately 10 degrees, said narrow ultrasonic beam projecting
said reference rod and adapted to reflect respective echo sig downwardly from the top towards the surface of the fluid to be
nals to said ultrasonic transducer in response to the incident measured, said ultrasonic transducer operating at a frequency
acoustic signal generated thereby. of approximately 59 KHZ.
19. An ultrasonic monitor to measure the level of a fluid in 25. The ultrasonic monitor recited in claim 19, further
a tank and comprising: 35 comprising an ultrasonic transceiver connected to receive an
an ultrasonic transducer adapted to generate an incident analog representation of the incident and return signals gen
acoustic signal towards the surface of the fluid within the erated by and reflected to said ultrasonic transducer, said CPU
tank and to receive a return signal reflected off the sur having an analog-to-digital converter connected to said ultra
face of the fluid; Sonic transceiver to receive said analog representation there
a central processing unit (CPU) being responsive to the 40 from in a condition to be digitized, whereby to enable said
incident and return signals generated by and reflected to CPU to determine the elapsed time of flight between said
the ultrasonic transducer for determining the elapsed incident and reflected signals and thereby calculate the dis
time of flight therebetween and calculating the distance tance from the surface of the liquid within the tank to said
from the surface of the fluid to the ultrasonic transducer ultrasonic transducer.
depending upon said elapsed time of flight; 45 26. The ultrasonic transducer monitor recited in claim 25,
an RF transceiver having an antenna and being interfaced wherein said ultrasonic transceiver includes a variable gain
with said CPU for receiving data therefrom correspond amplifier connected between said ultrasonic transducer and
ing to the distance calculated by said CPU, the antenna the analog-to-digital converter of said CPU, the analog rep
of said RF transceiver transmitting said distance data resentation of said incident and return signals being filtered
overa wireless communication path, said RE transceiver 50 and applied to said analog-to-digital converter by way of said
generating a wake-up signal in response to a particular variable gain amplifier.
ID polling signal transmitted to the antenna of said RF 27. The ultrasonic monitor recited in claim 25, wherein
transceiver when it is desirable to access the data corre said ultrasonic transceiver includes a temperature amplifier
sponding to the distance calculated by said CPU, said connected between said ultrasonic transducer and the analog
transceiver Supplying said wake-up signal to said CPU 55 to-digital converter of said CPU, an indication of the tempera
for causing said ultrasonic transducer to generate said ture within the tank at said ultrasonic transducer being
incident acoustic signal towards the Surface of the fluid applied to said analog-to-digital converter by way of said
within the tank and the resulting data which is indicative temperature amplifier.
of the distance calculated by the CPU to be supplied to
said transceiver for transmission by said antenna; and