Note: Descriptions are shown in the official language in which they were submitted.
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Long-term Seafloor Heat Flow Monitoring Probe Based on Underwater Robot
Platform
Technical Field
The present invention relates to the technical field of measurement of
seafloor hear flow, and in
particular relates to a long-term seafloor heat flow monitoring probe based on
an underwater robot
platform.
Background Art
Seafloor heat flow is an important component of terrestrial heat flow and
provides important basic
data for studying marine geodynamics, the evolution process of sedimentary
basins, the evaluation of oil,
gas and hydrate resources, and the hydrothermal circulation mechanism.
Seafloor heat flow can be
either measured by means of seafloor drilling or seafloor heat flow probes, or
calculated by means of the
bottom simulating reflection (BSR) of a reflection seismic profile. Although
the heat flow value obtained
by seafloor drilling (deep-sea drilling, petroleum drilling and the like of
ODP or DSDP) is less susceptible
to the action of the earth's surface shallow layer and has higher reliability,
fewer stations are distributed,
the cost is higher, and thus, its application is restricted; due to influences
from factors such as the
discontinuity of BSR, estimation errors in the thermal conductivity of
sediments and inconsistency of the
base of the gas hydrate stability zone, there is a certain difference between
the calculated results
regarding BSR heat flow in some sea areas and the measured heat flow values,
and the applicable
range of BSR is somewhat narrow; and relatively speaking, shipborne probe-type
seafloor heat flow
measurement is flexible in operation and lower in cost and has a measurement
range available to cover
part of a deep water zone, thereby being widely applied in sea areas around
the world.
Since the depth to which a heat flow probe is inserted into the sediments is
small (generally less
than 10m), the demand for a shallow seafloor environment is higher, and a
relatively constant ambient
temperature is required. The seafloor temperatures in most of deep water zones
are relatively constant,
but in shallow seas and part of deep water zones, the bottom water temperature
variation (BVVTV for
short) at the seafloor tends to be larger due to influences from the seasons,
daily temperature, flow,
waves, tides and other factors. For example, the monthly mean variation of
BVVTV in winter and summer
in part of the water areas deeper than 50m in the East Chain Sea may be as
much as 5 C; in the sea
area about 2900m deep in the Nankai trough of Japan, the fluctuation in the
bottom water temperature in
a year is also up to 0.8 C (FIG. 1); and after the bottom water temperature
fluctuations were monitored in
the Xisha and Dongsha sea areas in the northern South China Sea in 2013 and
2014, the research
group of the inventor found that the bottom water temperature variation in one
(with a water depth of
900m or so) of the stations reached 0.42 C within 48 hours. It shall be noted
that this is the fluctuation
observed only within a short time (about 2 days), and the amplitude of its
fluctuation should be larger
within a longer time scale.
What are the influences of BVVTV to the seafloor heat flow measurement
results? According to
previous studies, BVVTV will affect the geothermal gradient of surface
sediments through thermal
conduction in terms of temperature fluctuation amplitude and phase. The decay
of its amplitude follows
the exponential law, and the decay speed is related to the period of BVVTV.
BWTV is generally formed by
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the combined superposition of influencing factors of different periods.
Therein, a portion in a long period
decays slower with far-reaching influences; and a portion in a short period
decays faster. For example,
BWTV within a day as a period may only influence as deep as about 0.5m, and
BVVTV within a season
as a period may influence sediments at a depth of up to 8m to 9m. A common
seafloor heat flow probe
has a probing depth of up to 6m to 10m, and the influence of the short-period
BWTV may be basically
avoided after removing surface geothermal gradient data. However, for long-
period BWTV, conventional
seafloor heat flow probes may not penetrate through its influencing depth,
resulting in the measured
geothermal gradient not necessarily reflecting the thermal state of this site
truthfully. In this case,
conventional seafloor heat flow probes are not very suitable for obtaining
geothermal parameters in sea
areas with larger bottom water temperature fluctuations.
How to avoid the influences of BWTV to heat flow measurement? There are two
approaches: the
first is to find a way to increase the measurement depth as much as possible
to avoid the influencing
depth of the bottom water temperature on the surface; and the second is to
find a way to acquire the
fluctuation variation law of the temperature at different depths of the
surface sediments and then analyze
this data of long-term sequences to eliminate the influences of the bottom
water temperature fluctuations,
thereby acquiring reliable background geothermal information. In the first
approach, once the heat flow
probe is too long, its operation difficulty and other various problems will be
highlighted (such as
restrictions on equipment weight, implementation capacity of a research
vessel, condition of seafloor
sediments), and thus, it is not a very good solution. With the continuous
improvement of science and
technology, it has been possible to conduct long-term (more than one year)
temperature monitoring at
the seafloor, therefore, many scholars have started to develop long-term
monitoring equipment to
monitor and study the sea areas with larger bottom water temperature
fluctuations. This solution is
practicable and very meaningful at present.
Several representative pieces of equipment are selected and will be briefly
introduced below.
(1) Drilling-type long-term seafloor heat flow monitoring system
The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) employs a
reusable
drilling-based long-term temperature measurement technology (FIG. 2), and they
call it Circulation
Obviation Retrofit Kits (CORKs or ACORKs for short). A drilled hole is as deep
as several hundred
meters, and besides temperature sensors, various sensors for pore water
pressure and the like are also
installed for mainly monitoring the co-seismic effects of earthquakes, such as
the variations of
temperature, water pressure and the like at different depths of the drilled
hole before and after the
earthquake. Naturally, the obtained long-term temperature fluctuation data may
also be used for
explaining the geothermal distribution conditions without an influence from
the bottom water temperature
fluctuations. Core components of CORKs mainly include a data logger (including
a battery) and a sensor
string. During specific operation, under the assistance of an underwater
robot, a multi-sensor (including
temperature sensors) string type measurement instrument with a weight is
vertically lowered into a
hollow casing pipe of a seafloor drilled hole (for example, an IODP drilled
hole), a plurality of temperature
sensors are used to measure the ambient temperatures (or equilibrium
temperature) at different depths
of the drilled hole, and all the data is saved in the data logger in the mouth
of the hole. During recovery,
the underwater robot takes the data logger at the mouth of the hole back, and
replace it with a data
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logger having a new battery to realize long-term cycle measurement. In
addition, there is another
practice in which the entire sensor string is also taken out. This sensor
string often consists of a plurality
of self-contained miniaturized temperature measurement units (i.e. including
batteries and memories),
and the data is not stored in the data logger at the mouth of the hole.
The number of measurement channels of CORKs can be changed and replaced
flexibly, the
measurement depth can reach several hundred meters (depending on drilling
depth), and the equipment
can be reused a plurality of times at the seafloor to obtain plentiful data.
Nevertheless, its application
objective mainly lies in co-seismic monitoring, the distribution and quantity
of sites are limited by the
seafloor drilling, therefore, the application range is limited. Meanwhile, the
temperature measured
thereby is directed to water temperature at different depths in the drilled
hole, and this may also be
different from the actual temperature of a stratum at the corresponding depth.
(2) Pop-up type long-term seafloor heat flow monitoring system
The Yamano team from the Earthquake Research Institute of the University of
Tokyo in Japan
employs a pop-up type probe monitoring instrument to realize long-term heat
flow monitoring (FIG. 3),
and they call it PLHF (Pop-up Long-term Heat Flow instrument). In this piece
of equipment, six
thermistor temperature sensors are packaged in a slim metal probe with a
length of about 2m and the
sensors in the probe are connected with a recording unit in a recovery cabin
through watertight cables to
realize temperature collection. When the monitoring instrument is lowered, the
probe, a weight and the
recovery cabin are fixed together and then lowered into the sea from a
research vessel. Under the
pressure of the weight, the probe is inserted into the seafloor sediments.
During recovery, the recovery
cabin cuts the connecting wires between the sensors and the recovery cabin
through an electric cutter
and meanwhile discards the metal probe and the weight through an acoustic
releaser to realize the
pop-up of the recovery cabin.
With respect to the seafloor drilling-type long-term seafloor heat flow
monitoring solution above,
PLHF is the system truthfully taking the long-term seafloor heat flow
monitoring as an objective, which is
convenient and flexible in operation manner, and can be lowered and recovered
with the research vessel
as a carrier as long as sea conditions for operation are not too bad,
therefore, it is suitable for most sea
area operations. Nevertheless, this equipment depends on self gravity force to
realize the insertion of the
temperature measurement probe, which cannot be inserted successfully if the
seafloor sediments are
harder. Therefore, before lowering the PLHF system, it is normal to conduct
sediment investigation with
reference to the sediment thickness reflected by the seismic profile by using
a gravity sampler for
sampling. Moreover, this pop-up equipment is more complicated in structure and
needs to be awakened
through an underwater sound communicator during recovery, then, the electric
cutter is used to cut off
the sensor cables in the probe to realize separation between the weight and
the instrument cabin,
therefore, the requirements on the reliability and stability of the releasing
equipment is higher.
(3) ROV-based long-term seafloor heat flow monitoring system
During the cruise NT07-E1 of YK06-03 of JAMSTEC, a long-term seafloor heat
flow monitoring
system (FIG. 4) based on the operation of a shipborne cabled remotely operated
vehicle (ROV) was
used, and they called it LTMS (Long-term Temperature Monitoring System). This
system consists of a
data logger (including a battery and a temperature measurement circuit) and
two temperature sensor
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probes, and the sensor probes are connected with the data logger through a
watertight cable 2m long.
Six temperature sensors are uniformly arranged in the probe at an interval of
10cm, and the probe is
0.76m in length and 13mm in diameter and has a structure similar to that of
the probe of PLHF. During
operation, LTMS is carried to the seafloor by the ROV, which inserts the
temperature probes into the
sediments through a robot arm, with the data logger placed aside; and during
recovery, the ROV pulls
out the temperature probe heads and takes them back to the research vessel
together with the data
logger.
Compared with the pop-up type PLHF system, the LTMS based on ROV operation has
a relatively
simple structure and high success ratio in operation. But the LTMS is larger
in size and weight, has the
length, width and height of 1,20m X 0.43m X 0.51m together with a frame and
the data logger, and
weighs up to 22kg in the water and 39.6kg in the air. Nevertheless, the
carrying capacity of the ROV is
generally limited, resulting in it being difficult for the ROV with slightly
weak carrying capacity to carry out
the seafloor operations for other equipment during deployment and recovering
of LTMS. Therefore, it is
relatively high in operation cost and low in comprehensive operation
efficiency. Meanwhile, as the sensor
probe of PLHF, the plurality of temperature sensors are sealed in a metal tube
which is fully filled with
heat transfer oil and is more than 13mm in diameter; due to the isolation
effect of the oil and tube, the
response of the temperature sensors to the temperature variation of the
surrounding sediments is
lagged, and some high-frequency small-amplitude temperature variation signals
are filtered and
removed, resulting in a reduction of the temperature sensing sensitivity. But
after reducing the diameter
of the metal tube, it will be decreased in strength and easily break during
the insertion process.
Table 1 Brief comparison among the three types of long-term seafloor heat flow
monitoring solutions
Long-term monitoring
Applicable conditions or
Major advantages and disadvantages
equipment range
Drilling-type CORKs Advantages: the number
and interval of the Research vessel available
temperature measurement channels can be adjusted for seafloor drilling and
flexibly; the temperature measurement string is carrying the underwater
reusable; and the measurement depth is large, and robot.
the data is relatively reliable.
Disadvantages: the drilled holes are limited in
1 distribution and the drilling is high in cost;
Pop-up type PLHF 1 Advantages: the operation
is flexible and the Most sea areas with soft
requirement on the research vessel is low, sediments are applicable,
Disadvantages: the equipment is relatively and the requirements for
complicated in composition structure and has higher the research vessel and
requirements for system reliability; and the sensitivity the operation sea
and response speed of the sensors are plain. conditions are low.
ROV-based LTMS Advantages: simple
structure and high operation The research vessel
success ratio, and the core component of the needs to be provided with
equipment is reusable. an
underwater robot with a
Disadvantages: the size and weight are relatively
certain carrying capability.
large, resulting in lower comprehensive operation
efficiency and higher cost of the remotely operated
vehicle; and the sensor sensitivity and the response
speed are normal.
Table 1 briefly describes the characteristics and applicabilities of the three
types of long-term
seafloor heat flow monitoring systems as described above, and from Table 1. it
can be seen that each
type of equipment has respective advantages and disadvantages as well as
applicabilities, and
meanwhile undergoes different restriction conditions. The long-term seafloor
heat flow monitoring
equipment is developed towards the directions of wider application range,
higher success ratio and
efficiency, better temperature measurement sensitivity, portability,
compactness and the like.
With the development of science and technology and the upgrade and
popularization of offshore
operation equipment, the operation of shipborne underwater robots has become
mature gradually and is
undergoing rapid popularization. The underwater robots are classified into
shipborne ROVs (remotely
operated vehicles), AUVs (autonomous underwater vehicles) and manned
submersible vehicles, and
they have the functions of real-time image transmission and robot arm
operation and the like during
underwater operation, thereby bringing giant convenience to the seafloor heat
flow probing and greatly
improving the reliability and success ratio in the heat flow operation. In
future heat flow investigations,
underwater robots will play an increasingly important role, and developing
heat flow equipment based on
underwater robots will also be a development trend.
Summary of the Invention
With respect to the defects in the prior art, the objective of the present
invention is to provide a
long-term seafloor heat flow monitoring probe based on an underwater robot
working platform, which
structurally consists of a support probe lance and a plurality of self-
contained temperature measurement
units; the sensor packaging probe heads less than 5mm in diameter are in close
contact with the
sediments on the seafloor, therefore, the sensors are faster in response speed
to the sediment
temperature variation and have better accuracy.
To achieve the objective as described above, the present invention employs a
technical solution as
follows:
A long-term seafloor heat flow monitoring probe based on an underwater robot
platform, comprising
a support probe lance and a plurality of self-contained temperature
measurement units available for
long-term seafloor heat flow monitoring for more than 1 year, wherein the
plurality of self-contained
temperature measurement units are fixed on the support probe lance at equal
intervals in a spiral
distribution to form a distributed multi-point temperature measurement
structure for long-term monitoring
of temperature fluctuations of seafloor sediments at different depths; the
upper portion of the support
probe lance is a gripping handle, and the lower portion of the support probe
lance is a fixing tube in fixed
connection with the gripping handle; each self-contained temperature
measurement unit comprises a
casing, a battery, a temperature measurement circuit board, a sensor packaging
probe head and a
temperature sensor, wherein both the battery and the temperature measurement
circuit board are
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installed in the casing, the temperature sensor is installed in the sensor
packaging probe head and
electrically connected with the temperature measurement circuit board, and the
sensor packaging probe
head is fixed with the casing through a thread; and during long-term
monitoring work for the seafloor
heat flow, an underwater robot grips the gripping handle through a robot arm
so that the fixing tube is
inserted into sediments at the bottom of seawater, with the gripping handle
left in the seawater, the
sensor packaging probe head of one of the self-contained temperature
measurement units is disposed
upward for long-term measurement of bottom water temperature fluctuations on a
seafloor, and the
sensor packaging probe heads of the self-contained temperature measurement
units remaining are
disposed downward for long-term measurement of geothermal gradients.
The temperature sensors are installed in the sensor packaging probe heads,
which are less than
5mm in diameter to allow the sensors to come into close contact with the
seafloor sediments and to be
able to sense the temperature variation of the sediments quickly and
correctly; and a plurality of
miniaturized temperature measurement units are spirally arranged on the
support probe lance at certain
intervals, with the sensor packaging probe heads facing downwards to ensure
that the tip probe head of
each temperature measurement unit can always come into contact with the
sediments undisturbed
during the probe insertion process, thereby maximally guaranteeing the
authenticity of the heat flow
in-situ measurement of the sediments.
The self-contained temperature measurement units are installed on the support
probe lance through
U-shaped fasteners. The number and arrangement interval of the self-contained
temperature
measurement units can be adjusted flexibly for long-term monitoring of the
temperature fluctuation of the
seafloor sediments at different depths. Each temperature measurement unit
works independently in a
self-container manner to form a distributed multi-point temperature
measurement structure, so that the
damage of any one of the self-contained temperature measurement units will not
influence the normal
measurement work of other temperature measurement units. The self-contained
temperature units have
good interchangeability and universality to facilitate the dismounting and
maintenance of the equipment,
which is extremely advantageous to the practical operation of marine
equipment.
The temperature measurement circuit board in each of the self-contained
temperature
measurement units comprises a power module, a temperature measurement module,
an attitude
measurement module, a single-chip computer and a storage module, wherein the
battery supplies
power to the temperature measurement module and the attitude measurement
module respectively after
undergoing voltage conversion performed by the power module; data collected by
both the temperature
measurement module and the attitude measurement module is processed by the
single-chip computer
and stored by the storage module; and the single-chip computer is communicated
with an upper
computer through a communication interface module.
The power module as well as the temperature measurement module, the attitude
measurement
module, and the storage module are all electrically connected with a MOS tube
therebetween; a grid
electrode of each MOS tube is respectively connected with the output end of
the single-chip machine; a
drain electrode of each MOS tube is connected to the corresponding power
module; a source electrode
of each MOS tube is respectively connected to the power module as well as the
temperature
measurement module and the attitude measurement module.
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Each temperature measurement module comprises a reference voltage source U1
and an analog to
digital converter; the input end of the reference voltage source U1 is
connected with the power module;
the output end of the reference voltage source U1 is connected with the
positive reference end of the
analog to digital converter through a resistor R3; one end of the temperature
sensor and the negative
input end of the analog to digital converter are both grounded; the other end
of the temperature sensor is
connected to a portion between the resistor R3 and the positive reference end
through a resistor R2; the
negative reference end and the positive input end of the analog to digital
converter are both connected to
a portion between the resistor R2 and the temperature sensor; the output end
of the analog to digital
converter is connected with the single-chip computer; two ends of the
temperature sensor are connected
with a first capacitor in parallel therebetween; the output end and the
grounding end of the reference
voltage source U1 are connected with a second capacitor in series
therebetween; and the input end and
the grounding end of the reference voltage source U1 are connected with a
third capacitor in series
therebetween.
The attitude measurement module is a three-axis acceleration sensor HAAM-313B,
three-axis
output ends of which are respectively connected with three input ends of the
single-chip computer, and a
connecting wire between the attitude measurement module and the single-chip
computer is connected
with a filter capacitor having one end grounded.
The single-chip computer is STM8L151G.
Two-wire system serial communication between each of the self-contained
temperature
measurement units and the upper computer is implemented through the casing;
the casing comprises a
first metal casing with an open hole at the lower end, and a second metal
casing is filled in the open hole;
the second metal casing and the first metal casing are fixed there between
through a plastic casing; the
grounding end of the temperature measurement circuit board is connected on the
first metal casing
through a first electric wire; an RX/TX port of the single-chip computer is
connected to the second metal
casing through a second electric wire; and during communication with the upper
computer, the first metal
casing and the second metal casing are connected with the upper computer
through a third electric wire
and a fourth electric wire respectively.
The support probe lance has an overall length less than 1m, a total weight
less than 3kg and 8kg
respectively in water and air, and a maximum operating water depth of 3000m;
the number of the
self-contained temperature measurement units is 4 to 5; the sensor packaging
probe heads are all
disposed downwards; and the distance between two adjacent sensor packaging
probe heads is 20cm to
25cm.
Each of the self-contained temperature measurement units has an outer diameter
less than 2cm, a
length less than 22cm, and a weight less than 0.3kg and 0.5 kg respectively in
water and air.
The present invention relates to a long-term seafloor heat flow monitoring
probe based on an
underwater robot working platform, which is mainly used to acquire a long-term
fluctuation law of a
temperature profile of the seafloor sediments in sea areas with larger bottom
water temperature
fluctuations, eliminate influences of the bottom water temperature
fluctuations to the temperature
fluctuations of the seafloor sediments and finally acquire reliable seafloor
geothermal parameters
(geothermal gradient, seafloor heat flow and thermophysical property of the
seafloor sediments). The
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probe mainly consists of a support probe lance and a plurality of self-
contained temperature
measurement units and may conduct long-term heat flow monitoring for more than
one year. The probe
is deployed and recovered relying on the underwater robot, has the
characteristics of operation flexibility,
high operation success ratio, authenticity and reliability in temperature
measurement of sediments,
portability and the like, and can do a very good job in serving seafloor heat
flow probing. Meanwhile, the
self-contained temperature measurement units, as the core components of the
probe, can be applied to
not only the long-term monitoring of seafloor in-situ heat flow, but also long-
term temperature
measurements in many occasions such as continental and deep-sea drilling and
environment monitoring,
thereby having a broad application prospect.
Compared with the prior art, the present invention has the following
advantageous effects:
1) the probe provided by the present invention has a concise structure and is
portable and light,
thereby being very suitable for underwater robots to work with; and compared
with the pop-up type heat
flow monitoring equipment, the present invention has higher reliability during
seafloor probing;
2) the temperature sensors in the present invention are packaged in the sensor
packaging probe
heads having a diameter less than 5mm, thereby being able to come into close
contact with the seafloor
sediments and sensing the temperature variation of the sediments quickly and
correctly; and meanwhile,
the self-contained temperature measurement units are installed in a spiral
manner, guaranteeing that
each temperature sensor can come into contact with the sediments undisturbed;
and the two
characteristics maximally guarantee the rapidness and accuracy in the
temperature measurement of the
sediments;
3) the plurality of self-contained temperature measurement units independently
work in a
self-contained manner to form a distributed multi-point temperature
measurement structure for long-term
monitoring of temperature fluctuations of the seafloor sediments at different
depths, thereby being able
to eliminate the influences from the bottom water temperature fluctuations to
finally obtain reliable
background geothermal parameters, and moreover, the self-contained temperature
measurement units
are interchangeable after being calibrated, thereby facilitating replacement
and maintenance; and
meanwhile, the self-contained temperature measurement units may also be
applied to long-term
temperature measurement in many occasions such as continental and deep-sea
drilling and
environment monitoring, thereby having a broad application prospect;
4) the self-contained temperature measurement units have the property of low
power consumption
and a programmable sampling interval of is to 1h for temperature measurement,
and may continuously
work for more than one year on the seafloor under the circumstances that the
sampling interval is not
more than 10min;
5) the temperature measurement channels (the number of the self-contained
temperature
measurement units) and the temperature measurement interval in the probe
provided by the present
invention can be adjusted flexibly, and the self-contained temperature
measurement units are
interchangeable and universal, thereby facilitating maintenance and assembly
of the equipment;
6) the probe has an overall length less than 1m, a total weight less than 3kg
in water and less than
8kg in air, and a maximum operating water depth of more than 3000m; and the
number of temperature
measurement channels is 4 to 5, and the probe heads are spaced 20cm to 25cm
apart, thereby realizing
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flexible adjustment; and
7) the self-contained temperature measurement units are less than 2cm in outer
diameter and less
than 22cm in length, with the sensor packaging probe heads being less than 5mm
in diameter and
weighing less than 0.5kg in air and less than 0.3kg in water, thereby
achieving tiny size and portability;
and the self-contained temperature measurement units are less than 1mK in
temperature measurement
resolution, less than 5mK/year in long-term drift in temperature measurement,
and superior to 5mK in
channel consistency.
Brief Description of the Drawings
FIG. 1 is a temperature-time section of sediments in a shallow sea area of the
Nankai trough,
wherein (a) shows the original temperature fluctuation records of the
sediments at different depths; and
(b) shows the temperature distribution of the sediments after the bottom water
temperature fluctuations
are eliminated; CHI is the temperature measurement channel for the most
shallow layer, and CH7 is the
temperature measurement channel for the deepest layer.
FIG. 2 is a structural schematic diagram of drilling-type long-term seafloor
heat flow monitoring
equipment.
FIG. 3. is a structural schematic diagram of pop-up type long-term seafloor
heat flow monitoring
equipment.
FIG 4 is an ROV-based long-term seafloor heat flow monitoring system.
FIG. 5 is a structural schematic diagram of a long-term seafloor heat flow
monitoring probe based on
an underwater robot working platform of the present invention.
FIG. 6 is an enlarged view of a zone A shown in FIG 5.
FIG 7 is a structural schematic diagram in case of seafloor operation of the
present invention.
FIG. 8 is a structural schematic diagram of a self-contained temperature
measurement unit.
FIG. 9 is an elementary circuit diagram of a temperature measurement circuit
board.
FIG 10 is an elementary diagram of power management of a temperature
measurement circuit
board.
FIG. 11 is an elementary circuit diagram of temperature and attitude
measurement modules.
FIG. 12 is an elementary communication diagram of self-contained temperature
measurement units
and an upper computer.
Reference signs are as follows: 10. support probe lance; 11. gripping handle;
12. fixing tube; 20.
self-contained temperature measurement unit; 21. temperature sensor; 22.
sensor packaging probe
head; 23. temperature measurement circuit board; 231. power module; 232.
temperature measurement
module; 233. attitude measurement module; 234. single-chip computer; 235.
storage module; 236.
communication interface module; 237. upper computer; 24. battery; 25. casing;
251. first metal casing;
252. plastic casing; 253. second metal casing; 30. U-shaped fastener; 100.
seawater; 200. sediments;
300. underwater robot; and 400. robot arm.
Description of the Preferred Embodiments
The present invention will be further described below with reference to
specific embodiments.
CA 02946611 2016-10-27
With reference to FIG. 5 and FIG 6, a long-term seafloor heat flow monitoring
probe based on an
underwater robot working platform mainly consists of a support probe lance 10
and a plurality of
self-contained temperature measurement units 20 structurally.
The support probe lance 10 made of a rigid plastic material is mainly used for
fixing the plurality of
5 self-contained temperature measurement units 20, and is inserted into the
seafloor by the gripping of the
underwater robot 300. The upper portion of the support probe lance 10 is a
gripping handle 11 made
from a nylon handle having a diameter of 60mm and a length about 200mm,
thereby facilitating the
gripping of the robot arm 400 of the underwater robot 300, and effectively
reducing the weight of the
probe simultaneously; and the lower portion of the support probe lance 10 is a
fixing tube 12 made from
10 a rigid plastic lance or an anti-corrosion metal tube with a diameter
about 20mm and a length about
800mm, which is used for fixing the self-contained temperature measurement
units 20 and is inserted
into the sediments while being prevented from corrosion and damage caused by
the seawater.
The self-contained temperature measurement units 20 are fixed on the support
probe lance 10
through U-shaped fasteners 30. The plurality of self-contained temperature
measurement units 20 are
spirally installed along the support probe lance 10 at equal intervals, and
can be flexibly adjusted in
number and interval for long-term measurement of geothermal gradients and
bottom water temperature,
and data obtained is processed to possibly calculate the accurate background
geothermal information.
The sensor packaging probe heads 22 face downwards to ensure that the sensor
packaging probe head
22 at the tip of each self-contained temperature measurement unit 20 can
always come into contact with
the sediments undisturbed, thereby maximally guaranteeing the authenticity of
the heat flow
measurement of the sediments. This feature is an advantage that is not
possessed by the forgoing
long-term heat flow monitoring equipment.
With reference to FIG. 7, when used for long-term seafloor heat flow
monitoring, the underwater
robot 300 grips the gripping handle 11 through the robot arm 400 so that the
fixing tube 12 is inserted
into the sediments 200 at the bottom of the seawater 100, with the gripping
handle 11 left in the seawater
100.
With reference to FIG. 8, each of the self-contained temperature measurement
units 20 has
independent functions of temperature collection, data storage and the like,
and consists of an
anti-corrosion metal casing 25, a battery 4, a temperature measurement circuit
board 23, a sensor
packaging probe head 22 and a temperature sensor 21. Therein, both the battery
24 and the
temperature measurement circuit board 23 are installed in the casing 25; the
sensor packaging probe
head 22 is fixed at the lower side of the casing 25; the temperature sensor 21
is installed in the sensor
packaging probe head 22 and is electrically connected with the temperature
measurement circuit board
23; and the end portion of the sensor packaging probe head 22, far away from
the casing has 25, is less
than 5mm in diameter.
Each self-contained temperature measurement unit 20 has a tiny size and is
limited in carrying
capacity for the battery 24, therefore, the low power consumption property of
a circuit is the principal
element restricting its service life. To allow the temperature measurement
units to work for more than
one year continuously at the seafloor, the designed circuit is less than 10uA
in static power consumption,
less than 5mA in dynamic power consumption and less than 2s in dynamic working
time. In terms of a
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sampling frequency of every 10 min, the mean power consumption in one sampling
period is:
1=(10uA*(10*60s-2s)+5mA*2s)/10*60s=26uA. The maximum capacity of the battery
employed in the
allowable space is 800mAh; and in view of the low discharge rate and self-
discharge effect of the battery
in a seafloor low temperature environment, the electric quantity that can be
discharged by the battery in
the seafloor is approximately 600mAh, and the possible continuous working time
of a temperature
measurement circuit is t=600mAh/0.026mA/24h/365d=2.6 years.
The long-term seafloor heat flow monitoring probe based on the underwater
robot working platform
involved in the present invention has the following main design indexes:
(1) the number of the self-contained temperature measurement units 20 is 4 to
5, with a probe head
interval of 20cm to 25cm, therein, 3 to 4 self-contained temperature
measurement units 20 are used for
measuring geothermal gradients at an interval of 250mm, and 1 self-contained
temperature
measurement unit 20 is used for measuring bottom water temperature
fluctuations, and the sensor
packaging probe heads 22 thereof are placed close to the seafloor. The self-
contained temperature
measurement units 20 can be adjusted flexibly in number and arrangement
interval as required, and
meanwhile are interchangeable, thereby facilitating installation and
maintenance;
(2) the self-contained temperature measurement units 20 are less than 2cm in
outer diameter and
less than 22cm in length, with the sensor packaging probe heads being less
than 5mm in diameter and
weighing less than 0.5kg in air and less than 0.3kg in water, thereby
achieving tiny size and portability;
(3) the resolution is less than 1mK, the long-term drift in temperature
measurement is less than
5mK/year and the channel consistency is superior to 5mK;
(4) the sampling interval for temperature measurement is changeable from Is to
1h, and the
continuous working time on the seafloor is more than one year under the
circumstances that the
sampling interval is not more than 10min;
(5) the probe has an overall length less than lm, a total weight less than 3kg
in water and less than
8kg in air, and an operating water depth of more than 3000m; the whole set of
the probe is concise in
overall structure and has an open connection design that facilitates
assembling, dismounting, and
adjusting of the number and interval of the temperature measurement channels;
and with small size and
light weight, the probe is very suitable for an underwater robot to carry and
work with, and this is an
advantage that is not possessed by the forgoing LTMS and PLHF equipment.
The temperature measurement circuit board 23 employs a circuit theory as shown
in FIG. 9, and
mainly comprises the following modules: a single-chip computer 234 as a master
control module, a
temperature measurement module 232, an attitude measurement module 233, a
power module 231, a
storage module 235 and a communication interface module 236, and the specific
embodiment of each
circuit module based on a low power consumption design is as follows:
o Power module 231. As the electric property of a common electronic element,
the lower the
power voltage (within a reasonable range), the lower the consumed current is,
therefore, it is helpful to
save electric energy by supplying lower power voltage to the circuit. Taken
together, a circuit employing
a working voltage of 3.0V not only meets the power requirements of all devices
but also guarantees the
signal to noise ratio of the analog signal as much as possible.
In the case that the batteries 24 have the same size, the battery with the
lowest rated output voltage
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has a higher capacity, and thus has a longer service life, therefore, a
lithium ion battery with an output
voltage of 3.7V is employed in this design, which has the nominal capacity of
800mAh and the actual
discharge quantity of about 600mAh; and the lithium ion battery is subjected
to voltage conversion
performed by the power module 231 to producing a working voltage of 3.0V.
In the actual long-term seafloor heat flow monitoring, the circuit is in the
sleep mode most of the
time, and in case of long-term accumulation of micro static currents, quite a
lot of electric energy is still
wasted. Therefore, to maximally reduce static power consumption, it is
necessary to implement modular
power management for the circuit, and implement portioned time-sharing power
supply under the control
of the single-chip computer 234.
As shown in FIG. 10, the power modules for different functional modules (i.e.
the temperature
measurement module 232, the attitude measurement module 233 and the storage
module 235) in the
circuit are all independent, and each power supply is connected with a P-
channel MOS tube in series to
realize each power supply being able to be switched on or off independently
under the control of an I/0
port of the corresponding single-chip computer. When the circuit is in the
sleep state, the respective
power supplies of the temperature measurement module 232, the attitude
measurement module 233
and the storage module 235 can be switched off, and at this point, these
circuits basically consume no
current, thereby realizing minimal static power consumption.
z Single-chip computer 234. During the working process of the self-contained
temperature
measurement units 20, the single-chip computer 234 needs to possess the
following functions and
peripheral resources: synchronous serial communication (SPI) for data
collection, asynchronous serial
communication (UART) for data and command transmission, an analog to digital
converter for battery
voltage monitoring and attitude monitoring, a timing counter for precise time
delay, a real time clock
(RTC), a plurality of I/O pins for external input interruption and power
management, and at least 1KByte
of volatile random access memory (RAM). Therefore, it is necessary to choose a
single-chip computer
with a higher level of integration and simultaneously take the low power
consumption property thereof
into consideration.
A single-chip computer STM8L151 is employed in this design. Besides the
hardware functions as
described above, the single-chip computer also has multiple low power
consumption modes. Since the
temperature measurement units are in the sleep state most of the time when
working in the seafloor, the
application of the low power consumption mode can largely reduce the static
power consumption of the
temperature measurement units during sleeping.
Temperature measurement module 232 and attitude measurement module 233.
As shown in the elementary diagram in FIG. 11, to improve the temperature
measurement precision,
a low-noise reference voltage source U1 (with a model of ADR380) is employed
in each temperature
measurement module 232 to provide current excitation to a platinum resistance
sensor Pt1000 (i.e. the
temperature sensor 21). The input end of the reference voltage source U1 is
connected with the power
module 231; the output end of the reference voltage source U1 is connected
with the positive reference
end of the analog to digital converter through a resistor R3; one end of the
temperature sensor 21 and
the negative input end of the analog to digital converter are both grounded;
the other end of the
temperature sensor 21 is connected to a portion between the resistor R3 and
the positive reference end
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through a resistor R2; the negative reference end and the positive input end
of the analog to digital
converter are both connected to a portion between the resistor R2 and the
temperature sensor 21; the
output end of the analog to digital converter is connected with the single-
chip computer 234; two ends of
the temperature sensor 21 are connected with a first capacitor in parallel
therebetween; the output end
and the grounding end of the reference voltage source U1 are connected with a
second capacitor in
series therebetween; and the input end and the grounding end of the reference
voltage source U1 are
connected with a third capacitor in series therebetween. The resistor R3 plays
the role of current limiting,
and under its action, the working current of the platinum resistance sensor
Pt1000 is about 0.2mA,
allowing it to have a higher signal to noise ratio and reducing the power
consumption of the circuit. Since
each platinum resistance sensor Pt1000 and the corresponding temperature
measurement circuit board
23 are both packaged in the corresponding self-contained temperature
measurement unit 20, the output
impedance of the platinum resistance sensor Pt1000 is small, and due to the
shield effect of the metal
casing, a signal is less susceptible to external disturbances, therefore, the
voltage follower commonly
used in a signal conditioning circuit can be omitted, and the output signal of
the platinum resistance
sensor Pt1000 is directly fed into the AD converter, thereby reducing the
power consumption of the
circuit with the use of IC.
In each attitude measurement module 233, by making full use of the feature
that the single-chip
computer 234 is internally provided with a multi-channel AD converter, an
attitude sensor HAAM-313B
for outputting an analog signal is employed, and three axes of attitudes
signals x, y and z are directly fed
into the AD inside the single-chip computer after being filtered. These
measures can simplify the circuit
composition and reduce the power consumption while guaranteeing the
measurement precision.
Communication circuit. Each temperature measurement circuit board 23 is
installed in a cabin
body of a stainless steel pressure casing 25, and is in serial communication
with the upper computer
through the metal casing without opening the cabin (as shown in FIG. 12).
Specifically, each casing 25
comprises a first metal casing 251 with an open hole at the lower end, and a
second metal casing 253
that is filled in the open hole and is not in contact with the first metal
casing 251; the second metal casing
253 and the first metal casing 251 are fixed therebetween through a plastic
casing 252; this
communication circuit makes full use of the unique hardware half duplex serial
function (UART) of the
single-chip computer STM8 to directly connect an RYJTX pin and a circuit GND
of the single-chip
computer onto contact points of the second metal casing 253 and the first
metal casing 251 through
electric wires respectively; and the second metal casing 253 is connected with
the upper computer 237
through a third electric wire; and two-wire system serial communication is
realized by writing a
communication protocol corresponding to the upper computer. In this
communication circuit, it is
unnecessary to conduct long-distance and high-speed communication, therefore,
a serial chip does not
need to be added for communication signal conversion, thereby eliminating
electric energy loss caused
by a common serial communication circuit.
0 Storage circuit. A ferroelectric memory FM25V20 is employed for the storage
circuit. The
ferroelectric memory (FRAM) is a new-generation storage medium and combines
the advantages of the
nonvolatile data storage property of ROM and infinite reading/writing, high-
speed reading/writing and the
like of RAM together, and it is particularly important that it refreshes the
minimum working current (less
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than lmA during reading/writing operation) of the current leading storage
chip. FM25V20 has a storage
space of 2MB and can store a data volume of 24 months at the sampling rate of
every 10 min. Two units
of FM25V20 are employed in the storage circuit to enlarge the storage space,
and can store a data
volume of more than 3 years.
In addition, it is also possible to reduce the power consumption by optimizing
the storage program,
i.e. the single-chip computer accumulates the data collected each time in the
internal RAM until the RAM
is almost full, and then writes the data collected a plurality of times into
the memory once. In this way, for
the same data volume, less memory operation time is only needed in one-time
writing compared with
multiple writing.
In the probe of the present invention, the plurality of self-contained
temperature measurement units
independently work in a self-contained manner and are interchangeable after
being calibrated,
thereby facilitating replacement and maintenance; and meanwhile, the self-
contained temperature
measurement units 20 may also be applied to long-term temperature measurement
in many occasions
such as continental and deep-sea drilling and environment monitoring, thereby
having a broad
15
application range. (It should be pointed out here that there are many types of
long-term temperature
measurement equipment for the fields of drilling, environment monitoring and
the like as described
above at present, however, the self-contained temperature measurement units 20
involved in the probe
provided by the present invention have corresponding long-term temperature
measurement
performances and appearance conditions, and thus can be broadened in the
application range in the
20 fields as described above.)
The detailed description as outlined above is a specific description with
respect to the feasible
embodiments of the present invention, these embodiments are not intended to
limit the patent scope of
the present invention, and any equivalent implementations or variations made
without departing from the
present invention shall be encompassed in the patent scope of the present
case.
