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Description  |
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DESCRIPTION
1. Field of the Invention
The present invention relates to a liquid or powder measurement controlling
method and an apparatus thereof. More particularly, the invention relates
to a liquid/powder measurement controlling method and an apparatus which
are intended to have an improved measuring accuracy, an expanded measuring
range and a constant measuring time. These objects are obtained by
sequentially varying the flow velocities of substances to be measured on
the basis of an observed quantity obtained during the measurement.
The present invention also relates to a liquid or powder measuring mixer
for producing a new mixed liquid or powder by intermixing a variety of
stock liquids or powders after measuring these liquids or powders.
2. Background Art
A liquid can be measured by the use of a variety of systems, such as a
weight system (e.g., load cell), a pressure system. (e.g., differential
pressure transmitter), a capacity system (e.g., oval flowmeter) and so on.
For the measurement of a pulverulent body or fine powder, there is known
the weight system which mainly employs a load cell or the like.
In all these systems, however, the measurement control is performed on the
basis that the flow velocity is constant. A closed loop measurement
controlling system in which the flow velocities are successively varied
does not come under the above-described concept.
For the purpose of enhancing the measuring accuracy, the following
techniques have in the past been utilized.
In a first technique, as described, for example, in Japanese Patent
Publication No. 148019/1981, the flow velocity changes between two stages
and the measurement is made by a change-over to a slow flow velocity in
the vicinity of the target value.
In a first example of the first technique two kinds of devices have
different flow velocities. The change-over between the two is executed
when the deviation between the target value and the actual measurement
value reaches a given conditional value. In a second example of the first
technique, a single device has the capability to change-over the flow
velocity to two kinds of fixed conditions. The change-over is executed, as
in the first example, when the deviation reaches the given conditional
value. In a third example, based on the concepts of the first and second
examples, the conditional value for commanding the change-over is modified
from the previous measurement result by adding a learning function
identified as a software function.
In a second technique, such as disclosed in Japanese Patent Laid-Open
Application No. 29114/1982, there is an inflow level (also referred to as
a head quantity) used as a measurement halting condition. The measurement
technique is arranged such that the measurement is previously stopped in
anticipation of the inflow level. In a first example of the second
technique, the measurement stops when the deviation between the target
value and the actual measurement value reaches the given condition. In a
second example, the situation is almost the same as that in the third
example of the first technique. However, the conditional value for
commanding the halt of measurement is modified by an arithmetic
calculation based on the preceding actual measurement result.
In order to attain highly accurate measurement, the measuring device
applied to the liquid or powder measuring mixer has heretofore been
confined to such a type that the flow velocity of the liquid or powder is
limited and generally fixed. The measuring device of such a type that the
flow velocity is variable has not been seen so far.
Where liquids or powders are fed from a plurality of supply containers to
another container, a conventional type of liquid or powder measuring mixer
is required to have the measuring devices attached to the individual
supply containers.
For instance, when a capacity measuring system is used, as illustrated in
FIG. 1, two separate measuring devices are employed for the two kinds of
liquids or powders. There are required two control units with separate
control functions for two loops to predictively control the quantities
flowing into the mix container.
A "Liquid Adjusting Apparatus" and a "Method of Supplying Liquid" are
disclosed in Japanese Patent Laid-Open Application No. 74715/1981 and
Japanese Patent Publication No. 163426/1982, respectively. Based on the
above-described method and apparatus, the flow rates of the plurality of
liquids are sequentially measured by means of a common measuring device.
Liquid supply means attached to the respective containers to feed out the
liquids are controlled by independent control loops.
Namely, the flow rate of the liquid or powder differs according to the
quantity of liquid or powder stocked in the supply container, according to
the flow rate characteristics of the valve and according to liquid or
powder properties. Hence, a highly precise measurement cannot be expected
under the same control.
This situation is the same with a tank measuring system. It is required
that actuator stop valves attached to respective systems are controlled by
control systems of independent loops.
With a view to achieving a highly accurate measurement, there has been
proposed a method of performing change-over between two flow rates in
accordance with a predetermined measurement deviation by providing two
parallel valves, the flow velocities of which are different from each
other. Change-over between the two paths is executed at a predetermined
difference between the desired and measured amounts. In this case,
however, fulfillment of the control function requires the control of two
loops.
The reason why it is said that the control functions of two loops is
required is that when making use of a dispersive type control unit, two
separate control units are not necessary, because the measuring process
can be done in the single control unit. Judging form the number of inputs
and outputs and softwares as well, however the two separate control units
are required.
Further, there is disclosed in Japanese Patent Laid-Open Application No.
148019/1981 and Japanese Patent Laid-Open Application No. 155412/1981 a
control system for adjusting the flow rate of powders or by adjusting a
predetermined period at the next measuring cycle by computing a mean flow
rate from the total discharge weights of substances to be measured at a
given number of previous measuring cycles and from a time required and by
further obtaining a deviation between this mean flow rate and a target
value.
The flow rate of the powder, however, differs according to residual
quantities of the powder within the supply containers, the target value
properties of the powder. Hence, the highly accurate measurement cannot be
expected under the same control function.
In order to achieve a highly accurate measurement of powders, there is
proposed a method (Japanese Patent Laid-Open Publication No. 72015/1982)
of effecting a change-over between the two flow rates in accordance with a
predetermined measurement deviation. In this case, however, fulfillment of
the control functions requires the control of two loops.
However, in the conventional measurement control, the change-over is
carried out, as explained above, by making the flow velocity constant or
by varying the velocity in two stages. There arise, however, the following
problems inherent in the prior art measurement control, because the
measurement is fixed within a certain range.
A first problem is a lack of measuring accuracy. A situation arises where
the accuracy becomes unreliable due to fluctuations in flow velocity which
are caused by disturbances and variations in properties of the substance
to be measured, whether it be fluid or powder. In the case of gravity
transfer, the fluctuations in flow velocity are created in the measured
substance which flows out in accordance with the residual amount. This
residual amount is hereinafter in this specification referred to as a head
difference of the measured substance disposed in the container on the
upper stream side of the measuring point. If the head difference is large,
however, the flow velocity is in excess of the certain conditional range,
and accuracy is thereby degraded. This fact also results in the
restriction of the allowed variation of the head difference. In order to
keep the head difference within a predetermined scope, it is strictly
required that the measurement be stopped, or alternatively, the container
disposed on the upper stream side be properly resupplied with a raw
material. This also secondarily increases cost and causes a loss of raw
material.
Especially, the fluidity of a hygroscopic powder or of a powder subject to
bridging differs, depending on ambient storage conditions. In a system in
which the powder is used while being reserved in the supply containers,
its fluidity varies according to variations in ambient conditions, for
instance, temperature, humidity and vibrations caused by supplementary
devices such as a vibrator, an air knocker and so forth which are intended
to foster the fluidity. For this reason, flow conditions become different
and it follows that the measuring accuracy is degraded. To cope with this
degradation, restrictions are imposed for both duration of storage and for
the ambient conditions under which the device is installed in order to
maintain the measuring accuracy. This, as a result, increases the initial
costs and the running costs of the equipment.
A second problem is the restricted measuring range. Since the flow velocity
is restricted a ratio of the minimum to the maximum of the measurable
measurement value is approximately 1:5. In a 2-stage flow velocity system,
the ratio is approximately 1:10 at the most. The reason why the
measurement range is narrow will be explained as follows. Even if the
measurement is halted, an extra amount of the material continues to flow
in because of a delay of response of the system. This extra inflow
quantity is determined by the flow velocity. Hence if the target value is
small, the extra inflow quantity exceeds a guaranteed accuracy, and it
follows that the measuring range is restricted. Alternatively, the
allowable extra inflow quantity can be controlled by narrowing the
measuring range under the condition that the flow velocity is constant.
Where the same kind of liquid or powder is measured, multiple measuring
devices each having their proper measuring range are needed but this
multiplicity augments the number of devices. In production plants which
deal with a wide variety of materials, there are some measuring systems of
the type in which the ratio within the measuring range is about 1:100 at
most in the case of the same raw material. Therefore, it is necessary to
select the measuring devices within a range of target values.
A third problem is the lengthy measuring time. A measuring time is
contingent on the target value. When the target value is small the
measuring time is short, and vice versa. When the target value is small,
an operating time of the system is subject to scatter, whereby the
measuring accuracy is not assured. This also leads to a narrower
measurement range. Consequently, multiple appropriate measuring devices
are needed in accordance with the required measurement values, thereby
increasing the number of devices In the light of the entire system for
producing a new mixture by combining multiple already-measured substance,
the production capability is determined by the measuring time. Especially
in a pipeless transfer production system the carrying capability is
limited
The above-described defects further results in economic disadvantages in
terms of setting up the equipment for the process. Such is the prior art
arrangement that a multiplicity of independently controlled measuring
devices are provided in accordance with the target values and a separate
measuring device has to be prepared for every raw material or to provide
an optimum measuring time because of the restriction of the production
capability. Also, a separate measuring device is required for each supply
container. Hence, the system becomes complex and a large number of
measuring devices have to be available.
The situation is the same with a liquid tank or powder hopper measuring
system. It is required that stop valves attached to actuators in
individual systems be controlled by independent loop control systems (See
Japanese Patent Laid-Open Nos. 29114/1982, 163426/1983 and 74715/1981).
The prior art powder measuring mixer is equipped with the measuring devices
attached to the individual supply containers in order to feed the powders
from the receiving container (See Japanese Patent Application Laid-Open
Nos. 148019/1981, 155412/1981 and 72015/1982).
SUMMARY OF THE INVENTION
Accordingly, in view of the above difficulties, it is an object of the
present invention to provide a measurement controlling apparatus and
method for liquids and powders which is capable of attaining a highly
accurate measurement without being subject to fluctuations in flow
velocity that are produced due to disturbances and variations both in the
viscosity of the liquid or the fluidity of the powder; of ensuring a wide
measurement range; and of performing the measurement within a short period
of time without depending upon the magnitude of a target value.
To this end, according to one aspect of the invention, there is provided a
measurement controlling apparatus for accomplishing this measurement
controlling method.
The precise measurement controlling apparatus which constitutes the system
brings about a reduction in the number of mechanical elements, enhances
the capability of the equipment and decreases the loss of raw materials.
In accordance with this liquid and powder measuring mixer the system is
constructed by employing a measurement control unit for performing the
measurement in a short time regardless of the magnitude of a target value.
Thereby, the equipment is simplified, the production capability is
augmented, and a loss of raw materials is following significant economic
benefits:
(1) a decrease in initial cost which is derived from a reduction in the
number of devices,
(2) a decrease in the required maintenance which is attributed to the drop
in the number of devices,
(3) a decreased failure rate which is associated with improved reliability
and the reduction in the number of devices, and
(4) a decrease in running cost which is due to the drop in loss of the raw
materials.
The above-described object is accomplished by a liquid or powder measuring
mixer in which a small number of measurement control units momentarily
vary the flow velocity under closed loop control when measuring a liquid
or powder. The liquid or powder measuring mixer according to the present
invention is composed of the following components.
(1) Supply container (or tank): This container is designed for storing the
liquid or powder to be measured and has a capacity suited to the scale of
production. In accordance with the, present invention, there is no limit
on the residual quantity of the material remaining in the container.
Theoretically, the measurement is practicable up to a zero residual
quantity. There is no final influence caused by values of liquid material
property values (e.g., viscosity for a liquid or granularity for a
powder). Any kind of liquid or powder can be measured down to zero
residual quantity as long as the liquid or powder flows.
(2) Flow velocity control unit: The flow velocity control unit has several
flow velocity controllers, the number of which corresponds to the number
of the supply containers. For a liquid mixer, the flow velocity
controllers are opening control valves. The opening control valves are
intended to vary the flow velocity by changing a degree of opening
thereof. For a powder mixer, the flow velocity controllers may be a screw
feeder or a damper. In the screw feeder, the flow is controlled by issuing
a rotational frequency command. In the damper, the flow is varied by
changing the opening degree. A driving mechanism for the valves and other
flow controllers involves the use of, for instance, an AC servo motor.
(3) Change-over device: This change-over device helps a driving control
unit control the plurality of flow velocity controllers. If a driving
control unit is provided for every opening control valve or flow velocity
controller, the change-over device is not required. In some cases,
however, the change-over device is provided to reduce the costs.
(4) Measuring device: One measuring device is provided on the side of the
liquid or powder receiving container and measures the liquid or powder
sent from the plurality of supply containers. The measuring device
performs cumulative measurement of the weights of the mixed liquid or
powder. A tank or hopper measuring system employs a load cell a
differential pressure transmitter or a level gauge. An additional
measuring device may be fitted to a supply container, or alternatively the
supply container is mounted on a measuring board.
(5) The measurement control unit accomplishes precise closed loop
measurement control for varying the flow velocity and serves to measure
the respective liquids or powders with the aid of a single measuring
device. The plurality of liquids or powders can be measured by the single
measuring device in the same container so the number of devices can be
reduced. The change-over device is part of the measurement control unit.
(6) Liquid or powder receiving container (or tank): This container has a
capacity adapted to the scale of production. Mixable liquids or powders
are cumulatively measured. If cleaning is performed for every transfer of
the measured liquid, the measurement can independently be done in the same
container even in an unmixed state. Stirring and mixing may be conducted
in this container.
(7) Moving device: The moving device is designed for carrying the liquid or
powder receiving container. The moving device involves the use of an
unmanned carriage, a conveyor and so on. In connection with a carrying
mode, the liquid or powder receiving container itself may be movable, or
alternatively this movable function may be provided by a separate
structure.
The fundamental components of the present invention have been described
above but it is a basic concept that is employs a closed loop measurement
control unit for varying the flow velocity. In some cases, a wide variety
of other supplementary devices are provided.
For example, individual containers for liquids may be equipped with spray
bowls or the like for cleaning and change-over valves may be interposed in
the pipes. The respective liquid containers may be provided with stirrer
for mixing. Furthermore, hot water from a thermostatic oven may be
circulated for maintaining the temperature.
There are a wide variety of flow velocity controllers for varying the flow
velocity of a powder. The flow velocity controller may be a rotary system
in which a screw feeder changes the flow in response to a command of
rotational frequency. Another system, usable if the powder is highly
fluid, varies the flow by changing the opening degree of a damper in
response to a positional command. In addition, a shutter gate may be used
as a flow stopping type.
The condition that the flow velocity remain constant is the fundamental
factor which causes drawbacks inherent in the conventional measuring
device. In the measurement controlling method, however, the flow velocity
is variable under closed loop control, thereby attaining a highly accurate
measurement subject to no influence of fluctuations in flow velocity which
are caused by disturbances.
It further attains a wide range of measurement and a short time measurement
does not depend on the magnitude of the target value.
To accomplish the above, the measurement controlling apparatus is
characterized by the following system and components including a control
system, a detector and an operating device.
The control system may be defined as a non-linear type when modelling is
considered. Therefore, the actualization cannot easily be made by a prior
art simple PID control system.
To cope with this, an optimum manipulated variable is computed from a
deviation between the target value and the actual measurement value and
also from an observed quantity of the time variation of the deviation
under fuzzy control or learning control or optimum control. Subsequently,
the measurement control is accomplished by sequentially changing the flow
velocity to an optimum state in a continuous and descrete manner.
The detector serves to observe momentary variations in the measured value.
It is satisfactory that the detector is able to observe the measured
values of a load cell, a differential pressure transmitter and so forth.
However, the measuring range is contingent upon the static accuracy of the
detector.
The operating device is intended to vary the flow velocity. The operating
device is composed of mechanical parts and electric drivers although the
driving may be performed with a fluid like air or oil.
In the case of a liquid, a general practice is that the flow velocity is
varied by varying an opening. In this case, a valve to be used may involve
well known control valves assuming different configurations or a novel
valve having a notch-groove in its valve peripheral surface in a
valve-driving direction so that a flow rate can be varied. It is
sufficient for the well known valves to have common flow rate
characteristics except for quick opening. A satisfactory arrangement of a
valve is that the flow velocity successively varies from zero. There are
many kinds of other methods, but any apparatus capable of changing the
flow velocity from zero may be applicable.
Additionally, a moving device may be provided for moving the liquid or
powder receiving container is provided. The liquid or powder receiving
container can be carried by the moving device. (1) Hence, the liquid or
powder received from all the supply containers and are measured by using
no fixed pipes or ducts and consequently, there is created versatility in
equipment by decreasing the number of the receiving containers. In the
case of producing multiple liquids or powder bodies, mechanical play in
the equipment on the part of the receiving containers can be eliminated.
Besides, it is feasible to cope with changing processes while still
restricting an increase in the number of equipment to the utmost. (2) It
is possible to accelerate the measuring cycle by moving the receiving
container so that a change with passage of time can be minimized. (3) A
stirrer can be fitted to the container for receiving the liquid or powder
transferred from the supply containers, thus constituting an adjusting or
reaction tank. (4) For a liquid, there is no need for a connecting pipe
nor for its cleaning.
In a commonly used method in handling powder, a screw feeder varies the
amount of transfer of the powder by changing a rotational frequency of a
motor.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating a conventional measuring mixer.
FIG. 2 is a diagram illustrating a liquid measuring device applied to one
embodiment of the present invention.
FIG. 3 is a control block diagram illustrating a control method according
to the present invention.
FIG. 4 is a measuring characteristic diagram showing results of an
experiment conducted in accordance with the present invention.
FIG. 5 is a table illustrating measurement characteristics.
FIG. 6 is a block diagram of a dual liquid measuring device, illustrating
one embodiment of the present invention.
FIGS. 7 and 8 are flow-rate characteristic diagrams of valves applied to an
experimental measurement which is conducted by employing the device
depicted in FIG. 6. FIG. 7 showing a large flow velocity type valve and
FIG. 8 showing a small flow velocity type valve.
FIGS. 9 and 10 are diagrams, which correspond to FIGS. 7 and 8, showing
measurement results of the experiment.
FIG. 11 is a control block diagram illustrating a multiple liquid measuring
mixer according to the present invention.
FIG. 12 is a control block diagram illustrating a variant form of the
present invention for a liquid mixer.
FIG. 13 is a block diagram of a multiple powder body measuring mixer,
illustrating one embodiment of the present invention.
FIG. 14 is a control block diagram illustrating the measuring mixer
depicted in FIG. 13.
FIG. 15 is a flow-rate characteristic diagram when employing a screw feeder
for two kinds of powders.
FIGS. 16 to 18 are flow-rate characteristic diagrams illustrating results
of experiments conducted in accordance with the present invention for
powders.
FIG. 19 is a block diagram of the powder measuring mixer, illustrating a
variant form of the present invention.
FIG. 20 is a control block diagram illustrating the measuring device
depicted in FIG. 19.
FIG. 21 is a block diagram showing one example of a liquid measuring mixer.
FIG. 22 illustrates one example of a fixed powder measuring mixer.
FIG. 23 is a block diagram illustrating one embodiment of a movable liquid
measuring mixer according to the present invention.
FIGS. 24 and 25 are block diagrams illustrating two movable embodiments of
the liquid measuring mixer of the present invention.
FIG. 26 is a block diagram illustrating one embodiment of a movable powder
measuring mixer according to the present invention.
FIG. 27 is a block diagram illustrating closed loop control relative to the
embodiment of FIG. 26.
FIGS. 28, 29, 30 and 31 are diagrams used for explaining fuzzy control.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention will hereinafter be
described with reference to the accompanying drawings.
Turning now to FIG. 2, there is illustrated a liquid measuring device,
which is one embodiment of the present invention. The description will
concentrate on the case where a material filling a supply tank 1 provided
on the upstream side is transferred to a measurement tank 2 on the
downstream side, and a weight of the liquid is measured by a load cell 4
attached to the measurement tank 2.
A drain valve (DRV) 9 including a flow control valve (FCV) 7 serving as an
operating device for varying the flow velocity, a stop valve (SRV) 8 and a
cleaning/effluent valve (CVD) 10 are sequentially arrange on a piping path
between the supply and measurement tanks 1 and 2. The measurement tank 2
provided on the downstream side is equipped with the load cell 4 serving
as a detector for measuring the weight of the substance to be measured.
The load cell 4 is connected through a load cell amplifier 5 to a
measurement control unit 3. The measurement control unit 3 is connected to
a servo driver 6 and the flow control valve which constitutes the
operating device.
The measurement of the substance by the above liquid measuring device is
initiated by setting a target value to the measurement control unit 3 and
further by changing over the drain valve 9 and the cleaning/effluent valve
10 to the path to the measurement tank 2. The target value includes both
the weight of new material to be measured and the previous weight of the
measurement tank 2. That is, a cumulative weight measurement is performed.
Immediately when an indication of starting the measurement is given by the
measurement control unit 3, the stop valve 8 opens. Then, a positional
command is transmitted from the measurement control unit 3 to the servo
driver 6 so the the flow control valve 7 is set to a predetermined degree
of opening. A valve port of the flow control valve 7 is set in a specified
position by driving its servo motor, thereby controlling its degree of
opening. As a result, a flow of the raw material is caused. Then, the raw
material in the supply tank 1 begins to be transferred to the measurement
tank 2.
The load cell of the tank 2 detects the weight of the thus transferred raw
material and feeds back the value through the load cell amplifier 5 to the
measurement control unit 3.
The measurement control unit 3 computes both a deviation between the target
value and the measured weight value and also a time-variation of this
deviation. It further arithmetically obtains a valve opening degree
command (positional command) by which the flow velocity is set
appropriately at the next control cycle under fuzzy control or optimum
control or learning control. At the next control cycle, a new opening
degree command (positional command) is issued to the flow control valve 7,
thereby varying the flow velocity. A discussion of fuzzy control will be
deferred until the end of this patent.
As discussed above, the degree of opening of the flow control valve 7 is
controlled in a closed loop (FIG. 3) at the prescribed control cycle on
the basis of the observed quantity of the load cell 4. In consequence, the
flow velocity is successively and separately controlled at every
predetermined interval.
When the observed quantity is approximately equal to the target value, and
when the measurement deviation decreases the flow control valve 7 closes
its opening, resulting in a very small flow velocity. Hence, an inflow
quantity after stopping the measurement diminishes, and the measuring
accuracy is improved without being dependent upon the fluctuations in flow
velocity that are caused by a disturbance of, for instance, a head
difference.
In the measurement control unit 3 according to the present invention, the
operation of the flow control valve 7 is changed to achieve the target
value within a measuring range. The measurement can be conducted by the
same measuring device irrespective of the magnitude of the target value,
resulting in an expansion of the measuring range. This expansion should,
however, be within a static accuracy of the detector. Besides, the
operating pattern of the flow control valve 7 varies within the measuring
time, and the measurement can be performed within the same short period of
time regardless of the magnitude of the target value.
EXAMPLE 1
FIGS. 4 and 5 in combination show results of an experiment carried out for
verifying the above-described phenomenon.
The measuring device on which these results were achieved is capable of
performing 10 kg measurement at maximum, and the accuracy of the load cell
is 0.02%. The flow control valve is positionally controlled by the servo
motor, and the positional command is generated by the measurement control
unit.
FIG. 4 illustrates measurement characteristics obtained when 500 g and 1000
g measurements are made by the same measuring device if a liquid of 1.2 kg
is left in the upstream supply tank. The absicissa axis indicates the
difference between the target and measured values and the degree of
opening of the flow control valve, while the ordinate axis shows the
measurement time. As is obvious from the figure, the measurement can be
effected by the same measuring device irrespective of magnitude of the
target value. Therefore, the measuring range is expanded. As a matter of
course, a shift in valve opening differs, but it can be observed that the
measuring time is almost the same irrespective of magnitude of the target
value.
FIG. 5 shows the relation between the measurement accuracy and the
measurement time with respect to the target value. Note that the
measurement accuracy is obtained by measuring the outflowing liquid with
another weight measuring device.
In the case of the 10 kg measurement, the measurement time amounts to
approximately 130 sec., and the measurement accuracy is .+-.0.5 g. An
accuracy of .+-.1.0% is obtained over a measuring range of 1:100.
The flow velocity varies according to the residual quantity of material
remaining in the tank. However, even when initiating the measurement from
a different level of residual material, the measuring accuracy and the
measuring time do not change. It can be confirmed that there is no
influence of fluctuations in flow velocity.
The above-described embodiment has exhibited a positive measuring system
for measuring the liquid, that is, a system for measuring the liquid that
has flown into the measurement tank 2. Also, the drain valve 9 and the
cleaning/effluent valve 10 depicted in the figures are auxiliary valves
used for cleaning and effluent. In accordance with the present invention,
it will readily be assumed that instead of the positive measuring system a
negative measuring system may be utilized for measuring the amount of
outflowing liquid from the upstream supply tank by providing, as depicted
with a broken line in FIG. 2, a detector in the supply tank 1. The
detector may be a pressure-type in which the liquid level is measured by,
for instance, a level gauge in addition to weight measurement by using a
hopper and | | |
