DEVICE FOR MEASURING PERMEATE FLOW AND PERMEATE
CONDUCTIVITY OF INDIVIDUAL REVERSE OSMOSIS MEMBRANE
ELEMENTS
RELATED APPLICATIONS
This application claims priority to U.S. Provisional Application No. 60/781,858,
filed March 13, 2006, the entirely of which is hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
The present disclosure relates to a measuring device and system that allows
convenient and simultaneous measurement of flow and conductivity of permeate
produced by reverse osmosis elements while they are installed in a pressure vessel and
operated in an RO train.
Description of the Related Art
Spiral wound reverse osmosis membrane elements are widely used for the
desalination of water in plants of increasingly higher capacity. A commercial membrane
element measures 1000 mm (40 inches) in length and 200 mm (8 inches) in diameter and
weighs about 16 kg (40 lbs). A single element produces a permeate flow of 12m3/d - 24
m3/day (3200 - 6400 gallons per day). A single desalination plant producing 200,000
m3/day (50 million gallons of water per day) of permeate may require as many as 15,000
such spiral wound elements to produce the designed permeate capacity. The individual
elements are loaded into fiberglass pressure vessels arranged in racks to form a single RO
train. In large RO systems one train may consist of 100 - 200 pressure vessels. Several
trains may operate independently in any single desalination plant Six to eight elements
are loaded into a single pressure vessel. Accordingly, 600 to 1600 elements may operate
in a single train. Once loaded in the pressure vessels, membrane elements are only
removed at the time of element replacement (usually every 3-10 years of operation) or
when required for special testing. Removal of membrane elements from pressure vessels
requires the complete shut down of RO train operation.
The performance of individual elements is usually known prior to installation in
the RO system. After installation, the performance of elements may change due to
membrane fouling. The effect of membrane performance deterioration is observed by

measuring the permeate flow, permeate conductivity and pressure drop of a complete RO
train. In some cases, the permeate conductivity of individual pressure vends can be
measured. Measurement of permeate flow and permeate conductivity of individual
elements is not practical with current technology in a commercial RO unit Usually, the
effect of fouling on element performance is not uniform through the system. After
performance of an RO system has deteriorated to a certain level, a performance
improvement can be achieved by membrane cleaning or partial or complete replacement
with new elements. The major obstacle to efficient element replacement is the absence of
a convenient method for measuring the performance! of individual elements while they are
installed and operating in an RO train.
SUMMARY OF THE INVENTION
In an aspect, a system that permits assessment of performance of a reverse
osmosis membrane element is provided that comprises: the reverse osmosis membrane
element; a permeate tube within the reverse osmosis membrane element; an elongated
probing tube within the permeate tube of the reverse osmosis membrane element; at least
one sensor configured to measure a value used to assess the performance and disposed at
an inlet side of the probing tube; and a recording device in electronic communication with
the sensor so as to record results of the measurement.
In a former aspect, the sensor configured to measure a value used to assess the
performance comprises a mechanism for measuring permeate flow.
In a further aspect, the sensor for measuring permeate flow comprises a thermal
anemometer sensor.
In a further aspect, the system also comprises a sensor for measuring permeate
conductivity.
In a former aspect, the sensor for measuring permeate conductivity comprises a
conductivity cell with an integrally mounted thermocouple.
In a former aspect, a power source powers the sensor.
In a further aspect, the power source comprises at least one radio frequency
identification (RHD) tag.
In a further aspect, the electronic communication is conducted via wiring
connecting foe recording device and the sensor.
In a further aspect, the electronic communication is conducted via a wireless
connection connecting the recording device and the sensor.

In a further aspect, the tensor is additionally provided with an RFID tag, and the
value is linked to a reverse osmosis membrane element via communication between the
RFID tag and an RFID tag mounted on the element
In an aspect, a method of asgnssing performance of reverse osmosis membrane
elements is provided, the method comprising: providing a system in a pressure vessel, the
system comprising a reverse osmosis membrane element, a permeate tube within the
reverse osmosis membrane dement, an elongated probing tube within the permeate tube
of the reverse osmosis membrane element, at least one sensor configured to measure a
value used to assess the performance and disposed at an inlet side of the probing tube, and
a recording device in electronic communication with the sensor so as to record results of
the measurement; measuring at least one value; transmitting results of the measurement to
the recording device; and assessing the performance based on the results.
In a further aspect of this method, at least one value comprises data relating to
permeate flow.
In a further aspect of mis method, at least one value additionally comprises data
relating to permeate conductivity.
In a further aspect of mis method, the sensor is additionally provided with an
RFID tag, and the value is linked to a reverse osmosis membrane element via
communication between the KFID tag and an RFID tag mounted on the element
In a further aspect of this method, the method additionally comprises replacing the
element if the assessment indicates replacement is required to improve system
performance.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial schematic and partial block diagram of one embodiment of a
thermal anemometer that may be employed in the measurement system.
FIG. 2 is a graph illustrating the cyclic operation of the probe in the thermal
anemometer.
FIG. 3 is a graph of the characteristic temperature decay of a thermocouple probe.
FIG. 4 is a semi-log plot of the normalized temperature decay of a thermocouple
probe.
FIG. 5 is a block diagram of one logic circuit mat may be employed in a thermal
anemometer useful in a measurement system in accordance with an embodiment

FIGS. 6-10 are embodiments of sheath type probes that may be employed in the
thermal anemometer.
FIG. 11 is a flow chart of the operation of the thermal anemometer.
FIG. 12 shows a schematic view of an arrangement of reverse osmosis membrane
elements in a pressure vessel.
FIG. 13 shows the configuration of an integrated thermal anemometer sensor and
conductivity sensor device mounted on a support
FIG. 14 shows a schematic view of an arrangement of a thermal anemometer
sensor mounted on a support tubing inserted in the permeate tube of an RO membrane
element
FIG. is shows a schematic block diagram of a conductivity probe that may be
used in a measuring system in accordance with an embodiment
FIG. 16 shows a schematic diagram of temperature compensation circuits of the
conductivity probe of FIG. 15.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Embodiments comprise an integrated sensor device that enables simultaneous
measurement of permeate flow and permeate conductivity inside the permeate tube of
membrane elements, while the elements are in operation in the RO unit Particularly
preferred embodiments comprise a thermal anemometer sensor and conductivity sensor
mounted on an elongated small diameter support tubing. This sensor device can be
inserted through a permeate port of a pressure vessel into permeate tubes of membrane
elements operating and connected together in a pressure vessel. As the sensor is moved
along the permeate tube it generates electric signals mat are related to the permeate flow
rate and permeate conductivity at various points along the pressure vessel. The electric
signal is either transmitted through the wires connecting the sensors with an outside
recording device or by generating and sending a wireless transmission of the measured
data.
The electric energy required to power the thermal anemometer sensor and
conductivity sensor (collectively described as the "measuring devices") can be supplied
by radio frequency radiation, a rechargeable battery, power transformed from a radio
frequency identification (RFID) tag, electromagnetic energy, energy from a turbine
mounted on the small diameter support tubing, or other forms of energy supply known to
those skilled in the art. The measuring devices of preferred embodiments are preferably

powered by RFID tags. The RFID tags are preferably activated by electromagnetic energy
emitted by devices that retrieve information from RFCD tags, such as a receiver situated
inside or outside the pressure vessel. When activated, the RFID tags preferably transmit
power to the measuring devices, which take their measurements. In particularly preferred
embodiments, the data is stored in the RFID tags, which may be instantaneously and/or
later retrieved. In other preferred embodiments, the measuring devices are powered by
rechargeable batteries. For example, such batteries include, but are not limited to, nickel
cadmium batteries, lithium ion batteries, and other batteries known to those skilled in the
art. In preferred embodiments the batteries may be recharged by energy transmitted from
activated RFID tags. In other preferred embodiments, the measuring devices may be
activated by radio frequency (RF) energy from an outside source. Further embodiments
comprise measuring devices which are powered by magnetic energy, electromagnetic
energy, or other forms of energy known to those skilled in the art.
ID an embodiment of the device, the permeate flow is measured using a thermal
anemometer. Examples of such devices are disclosed in patents 5,271,138; 4,794,794;
4,848,147; 4,621,929; and 4,537,068, which are incorporated in their entirety by
reference.
In general, a thermal anemometer measures fluid velocity by sensing the changes
in heat transfer from a small, electrically-heated element exposed to the fluid.
If a wire is immersed in a fluid and is heated by an electric current, the
temperature of the wire increases and the power input is:

Where:
I: value of electric current,
Rw: resistance of the wire
hw: heat transfer coefficient of the wire
Sw: the surface area of the wire
Tw : temperature of the wire
Tf : temperature of the fluid
The resistance of the wire is also a function of temperature:

Where:

Ro is resistance of the wire at the reference temperature
α is coefficient of thermal resistance of the wire
To is the reference temperature
The heat transfer coefficient of the wire hw is a function of the fluid velocity vf
according to the following equation:

where a, b and c are coefficients obtained by calibration.
Combining the above three equations we can eliminate heat transfer coefficient hw
and rearrange to solve for fluid velocity:

The cooling effect produced by the flow passing over the element is balanced by
the electrical current to the element, so that the element is held at a constant temperature.
The change in current due to a change in flow velocity shows up as a voltage at the
anemometer output.
An embodiment of a thermal anemometer suitable for use in the device for
measuring permeate flow and permeate conductivity will now be described. Referring to
PIG. I, one embodiment of a thermal transient anemometer fluid flow measuring device
useful in preferred embodiments is designated generally by the reference numeral 10. The
device 10 includes a thermocouple sensing probe 12 which can be inserted into a fluid
flow path, illustrated by arrows 14 to measure the flow velocity.
The fluid flow 14 can be contained in a conduit or duct 16, such as a permeate
tube. The thermocouple probe 12 includes a pair of calibration wires 20, 22 which are
connected to form a conventional thermocouple junction 24 located adjacent to me end of
the probe 12.
In mis embodiment, the thermocouple 12 is illustrated as being a sheath type
probe, specific examples of which are illustrated in FIGS. 6-10. An unsheathed probe
also could be utilized. The sheath protects the junction 24 from the effects of the fluid
flow 14.
A simple, preferably electronic, control unit 26 is illustrated in block form. The
control unit 26 may be located at a site remote from the thermocouple probe 12, as shown
for example in Figure 14, in which the thermocouple probe is located at the distal end of
support tube 173 and control unit 26 may be located within recording device 174. The

unit 26 includes a power supply 28 which is coupled to one of the wires 22 through a
pulsing switch 30.
The unit includes a voltage measuring instrument 32, which is coupled to a
voltage versus time recorder 34. The voltage and time measurements are coupled to a
calculation unit 36, which correlates the fluid flow velocity from the temperature decay or
time constant of the probe 12. The calculation unit 36 is coupled to an output or display
unit 38, which can generate a visual and/or hard copy output.
The cyclic operation of the device 10 and the probe 12 is best illustrated with
respect to FIG. 2. At a time t1, the pulse switch 30 is closed, coupling a relatively high
voltage puke across the wires 20 and 22 for a time period of (to -t1). The temperature of
the probe 12 near the junction 24 is raised by resistance heating to a temperature above
that of the fluid to be measured. For example, in typical fluid flow measurements, the
temperature of the probe can be raised 5 to 10° F above that of the fluid. As described
hereinafter, the power pulse does not require accurate control or measurement
At-time to, the switch 30 is opened to remove the power from the wires 20, 22.
When the power is removed, the temperature distribution in the thermocouple 12 begins
to relax. At time t1 the temperature T1 of the junction 24 is measured by the instrument
32 which couples the measurement to (he recorder 34. At a second time t2, the
temperature T2 of the junction 24 again is measured by the instrument 32 and again is
coupled to tile recorder 34.
The two measurements, T1 and T2, then are utilized in the unit 36 to calculate the
corresponding flow velocity of the flow 14 in accordance with the analysis provided
hereinafter with respect to FIGS. 3 and 4. At time t3, the cycle again can be repeated if
desired. The temperatures T1 and T3 are totally unrelated and do not need to be the same
value. A second conventional reference thermocouple junction may be required where the
fluid bulk temperature is not substantially constant.
A mathematical analysis of the temperature decay of the junction 24 is
characterized by the graph illustrated in FIG. 3. Initially, at time to, the junction 24 has
some arbitrary temperature profile described by a temperature function, f(r). Modeling
the probe 12 as an infinitely long, homogeneous solid cylinder, the temperature
distribution as functions of radius 'r' and time 't' can be described by the classical series
solution of equation 5 below. This discussion is made under the zero reference theory,
where the fluid temperature is assumed to be zero, so that the probe temperature T

actually represents a difference from the reference temperature. In actual practice, the
fluid temperature would be measured and known, so that the corresponding measured
difference between the fluid and probe temperatures could easily be correlated
mathematically.
Where:
T=temperature differential between probes and fluid at given radius and time
r=radius
a=outside radius of cylinder
t=time
H=convective coefficient at cylinder surface
h=HTK
k=K/pC
p=density
C=heat capacity
K=thermal conductivity within the cylinder
Jo=Bessel function of order zero
αn=roots of the transcendental equation 2

After a sufficient decay time, to-t1, the initial temperature conditions in the probe
12 relaxes and all terms, in the same series, approach zero, accept one. The decay
equation after time, t1, can be approximated by:

where

A1 is a constant for fixed initial conditions, flow conditions and radial position, r;
and α1, is the smallest root (eigenvalue) of the transcendental equation 6.
A semi-log plot of equation 7 starting at time, t1, and normalized to T1, is shown
in FIG. 4. The slope of this curve is constant and approximated by equation 8.

Significantly, the initial conditions cancel and, therefore, the slope is independent of the
power pulse's shape, duration, radial position and magnitude. Utilizing equation 8 and
from equation 6 recognizing that H is a function of a,, the convective coefficient, H, can
be determined by using equation 8 A.

From fluid dynamic considerations, the convective coefficient at the surface of the
probe can be approximated using a correlation for fluid cross flow over a cylinder in the
form of equation 9.

Where
Re=vd/γ (Reynolds Number) (9A)
d=outside diameter of cylinder
v=local fluid velocity
γ=dynamic viscosity
and C and n are known empirical constants over large ranges of Re numbers. Substituting
equation 9A into equation 9 yields equation 10.

Thus, with measured temperature values, T1 and T2, the local flow velocity, v, can
be calculated using equations 6, SA and 10.
For small internal thermal resistances (Biot #=bd<1) local fluid velocity is
approximately related to the slope in equation 8 utilizing equation 11. Hence, for fixed
fluid and probe properties, a log-log plot of v vs. slope, results in a straight line with slope
n.
The above constant is a calibration constant dependent upon fixed probe and fluid
properties. A database for different fluids and/or fluid temperatures can men be

developed. The exponent 'n' is a known constant over large ranges of Re numbers and is
given as 0.466 for the range of Re numbers from 40 to 4,000.
Thus, with measured normalized slope values (from equation 8) the local flow
velocity, v, can be calculated using equation 11. The total flow in the duct 16 based upon
the local velocity reading or readings then can be calculated utilizing Quid conditions,
duct size, probe location, etc. as utilized in many conventional flow measurement
methods.
A generalized block and schematic logic circuit of another embodiment of an
anemometer which may be used in an embodiment is designated generally by the
reference numeral 40 in FIG. 5. A thermocouple junction 42 is coupled by a pair of
calibration wires 44 and 46 to an amplifier 48. The wire 44 conveniently can be grounded
and the wire 46 is coupled to a pulse switch SO via a line 52. The pulse switch SO is
coupled to a power supply 54 via a line 56.
The amplifier 48 is coupled via wires 58 and 60 to an analog-to-digital converter
(A/D) 62. The output of the A/D converter 62 is coupled to a processor 64 via a line 66,
The processor 64, such as a microcomputer or microprocessor, also is coupled via a line
68 to the switch 50 and via a line 70 to a display 72. Although not illustrated, appropriate
filtering can be provided at the input to the amplifier 48 to isolate the amplifier 48 from
the transient power pulses applied to the junction 42, if desired.
in the device 40, the processor 64 controls the timing of the pulses applied to the
junction 42 by the pulse switch 50 and the power supply 54. The voltage from the
junction 42 is amplified by the amplifier 48 and converted into digital signals to be
utilized by the digital process which then can be displayed in the display 72. Although
digital signals are most preferable along with the utilization of a microprocessor for the
processor 64, an analog logic processor also could be utilized in which case the processor
64 and associated circuitry could be eliminated.
The devices 10 and 40 have good stability, repeatability and sensitivity. The
devices 10 and 40 readily can be adapted for simultaneous multiple flow measurement
techniques. Thermocouples have an established history of reliability, accuracy and
durability and the devices 10 and 40 benefit from the incorporation of the thermocouple
concept Specific thermocouple designs are illustrated in FIGS. 6-10.
In conventional thermocouples, the entire thermocouple length is heated by
applying sufficient power thereto. A decrease in power consumption can be obtained by

heating only the tip area of the thermocouple around the thermocouple junction. The
following probes described especially in FIGS. 6-10 are designed to utilize standard
fabrication techniques to minimize manufacturing costs. The utilization of sheath type
thermocouples allows their established history of reliability, accuracy and durability to be
incorporated into the devices 10 and 40. Further, the thermocouples are modified to
minimize the power requirements for decreasing operating costs and to enhance portable
battery powered applications.
Referring to FIG. 6, a first embodiment of a sheath type thermocouple probe 74 is
best illustrated. The probe 74 includes a sheath outer body 76 ending in a closed tip 78.
A first calibration wire 80 is formed to have a relatively low electrical resistance by
forming the wire 80 from a highly conductive material and/or a large wire diameter. A
second calibration wire 82 is formed to have a relatively high electrical resistance by
forming the wire 82 from a poor conductive material and/or a small wire diameter.
A junction 84 is formed adjacent the tip 78 and me wire 82 is grounded to the tip
78 and hence the sheath body 76. The tip 78 is locally heated adjacent the junction 84.
The local heating of the tip 78 is accomplished by applying a relatively high voltage
across the low resistance wire 80 and the sheath body 76. The current thus flows through
the wire 80 to the junction 84 with negligible resistance heating. From the junction 84,
the current flows through the high resistance wire 82 to the grounded tip 78. The wire 82
is thus heated between the junction 84 and the tip 78 to locally heat the tip 78. The
current flow through the sheath body 76 generates a minimal or negligible resistance
heating. The temperature sensing of the probe 74 is performed by utilizing the Seebeck
effect between the wires 80 and 82 at the junction 84.
A second embodiment of a sheath type thermocouple probe 86 is illustrated in
FIG. 7. The probe 86 includes a sheath body 88 with a tip 89. A first low resistance
calibration wire 90 is connected at a junction 92, just prior to the tip 89, to a high
resistance wire portion 94 which is grounded to the tip 89. A second low resistance
calibration wire 96 is also grounded to the tip 89.
The local heating of the tip 89 during the applied power pulse is accomplished by
applying a relatively high voltage across the wires 90 and 96. Due to the high electrical
conductivity of the wires 90 and 96, the only significant resistance heating occurs in the
high resistance wire portion 94 adjacent the tip 89. The temperature sensing of the probe
86 is accomplished by utilizing the Seebeck effect between the wires 90 and 96. The wire

96 also can be eliminated and the voltage then can be applied across the wire 90 and the
sheath body 88.
A third sheath type thermocouple probe embodiment is designated generally by
the numeral 98 in FIG. 8. The probe 98 also has a low resistance sheath body 100,
however, the probe 98 has a tip 102 formed from a high electrical resistance material. A
pair of low resistance calibration wires 104 and 106 are grounded to the tip 102. The tip
102 is locally heated by applying a relatively high voltage across the wires 104 and 106
which are of high conductivity causing the only significant resistance heating to occur in
the tip 102. Temperature sensing is again accomplished by utilizing the Seebeck effect
between the wires 104 and 106. Alternatively the voltage can be applied across me sheath
body 100 and one of the calibration wires, which eliminate the need for the other
calibration wire to be formed of a low resistance wire.
Another sheath type probe embodiment 108 is illustrated in FIG. 9. The probe
108 includes a sheath body 110 having a tip 112. A pair of relatively low resistance wires
114 and 116 are connected adjacent the tip 112 by a portion of high resistance wire 118.
The tip 112 is locally heated by applying a relatively high voltage pulse across the pair of
wires 114 and 116 which resistance heats the portion 118 to in turn heat the tip 112.
Temperature sensing of the probe 108 again is accomplished by utilizing the Seebeck
effect between the pair of wires 114 and 116.
A film embodiment of a sheath type thermocouple probe 120 is illustrated in FIG.
10. The probe 120 includes a sheath body 122 having a tip 124. A Low electrical
resistance wire 126 is grounded to the tip 124. To accomplish local heating of the tip 124,
either the tip 124 can be a high resistance material such as the tip 102 (FIG. 8) or the wire
126 can include a high resistance portion at the tip such as the wire portion 94 (FIG. 7). A
pair of calibration wires 128 and 130 are utilized for temperature sensing by utilizing the
Seebeck effect between the wires 128 and 130.
Alternatively, four or more multi-wire configurations also can be utilized. For
example, two wires can be utilized for providing the power pulse and two separate
calibration wires can be utilized for the Seebeck effect temperature sensing. Another
alternative is leaving the calibration wires 128 and 130 ungrounded in a similar fashion to
a conventional ungrounded thermocouple.
A flow diagram of the operation of the flow measuring device 10 is illustrated in
FIG. 11. The thermocouple (t/c) 12 is first pulsed as indicated by a block 146 such, as

over time period to -t1 in FIG. 2. The temperature is then measured, as indicated by a
block 148, at least twice, such as at times t1, t2, etc. in FIG. 2, as the junction temperature
decays. The slope of the decay curve is then calculated as indicated by a block 150, in
accordance with Equation S. The fluid velocity then is determined from the slope, as
indicated by a block 152 in accordance with Equation 11.
The velocity determined from each power pulse set of measurements men can be
displayed as indicated by a block 154. Alternatively or in addition, the velocity
determined by a power pulse can be stored and averaged with succeeding pulse
measurements, as indicated by a block 156. Each velocity value can be displayed, and the
average also can be displayed, or only the average velocity need be displayed. The
average can be a running average or can be for a fixed time period. After each velocity is
determined, the sequence again can be repeated as indicated by a line 158.
Modifications and variations are possible in light of the above teachings. The
heating of the probes can be effected as described by electrical resistance heating (Joule
heating). The heating or cooling of the probes relative the fluid also can be effected by
Peltier heating or cooling. The sheath type probes can include a conventional potting
material if desired. The calibration wires generally are formed from thermocouple alloys.
The addition in some probe embodiments of a separate wire portion or the probe tip
between the calibration wires, does not affect the measurement as long as the junctions
are maintained substantially at the same temperature. It is therefore to be understood mat
thermal anemometers useful in preferred embodiments include those that are otherwise
than as specifically described.
Alternate embodiments of the flow meters comprise rotatable members. Such
liquid flow meters can comprise an impeller or turbine mounted in the liquid flow path
and the inlet end of the support tube, wherein the number of rotations of the impeller or
turbine provide a measure of the liquid flow volume therethrough. The liquid flow meters
may provide an electrical circuit for detecting the rotation of movement of me impeller or
turbine, wherein it is typical to connect a magnetic element to the rotatable shaft and to
provide a coil or inductive pickup circuit in proximity to the magnet, wherein the rotating
magnet generates varying magnetic fields to influence the circuitry coupled to the pickup,
and to thereby generate electrical signals representative of shaft rotation. The electrical
signals are subsequently amplified and converted to drive signals for energizing some
form of indicating device, such as an RFID tag.

One embodiment comprises a liquid flow meter, wherein a magnet is affixed to the
rotatable impeller shaft. A magnetic field sensor, in the form of a ferromagneto resistive
circuit, is placed in physical proximity to the rotatable magnet, and the magnetic field
induces an electrical signal in the sensor, which signal is amplified and shaped to drive a
suitable logic network, the logic network serving to both count the sensed signals and to
calculate a corresponding flow volume indication.
Another embodiment of the flow meter utilizes magnets. For example, a first
magnet is affixed to the rotatable impeller shaft, and a second magnet is placed in
proximity to the first magnet, but outside of the liquid flow chamber. Rotation of the
second magnet is induced by the rotating field of the first magnet, and the rotating field
generated by the second magnet is detected by an inductive sensor to generate an
electrical signal representative of the shaft rotation. The electrical signal is then utilized to
drive an indicator circuit to provide a readout of the volume flow detected by the device.
Another embodiment comprises a flow meter utilizing shaft-mounted magnets.
For example, a meter has a first magnet attached to a rotor shaft and a second magnet
attached to as indicator shaft, the second magnet being rotatably and magnetically
coupled to the first magnet, so as to provide corresponding rotation of the indicator shaft
when the rotor shaft is rotated by the flow of fluid through the meter housing.
Another embodiment comprises a liquid flow meter of the rotating turbine or
impeller type, wherein liquid flow through the meter results in positive rotatable
displacement of a shaft made from a nonmagnetic material. A permanent magnet is
embedded proximate one end of the shaft, and the impeller end shaft is rotatably mounted
in a housing made from nonmagnetic materials. A magnetically-operated reed switch is
positioned outside the housing proximate the shaft end embedding the permanent magnet,
and each complete revolution of the shaft causes two magnetically-induced closures of the
reed switch. The reed switch is electrically coupled to a battery-operated logic circuit,
including counters and an electronic readout, so that switch closures of the reed switch are
converted into flow volume data provided to an RFID tag, for example.
The internal design of the rotatable impeller and flow meter cavity are controlled
to provide predetermined volumetric displacement characteristics, wherein each
revolution of the impeller is matched to the logic circuit so as to provide a predetermined
fractional relationship between the liquid flow volume passed during a single revolution
of the shaft and the unit of measure in which the logic circuit and display are adapted to

count and display unite. The unit of measurement may therefore be modified by merely
changing one linear dimension of the rotatable turbine or impeller.
Preferred embodiments also comprise measuring devices which monitor the
electrical properties of the permeate stream. The operation of devices that measure water
conductivity are preferably based on a measurement of the water resistivity between two
electrodes. A resistivity measuring sensor can preferably be mounted at the some position
as the flow measuring device. As described above, the permeate flow is measured using a
thermal anemometer.
Preferred embodiments of a permeate conductivity measuring device comprise
measuring devices which monitor the electrical properties of a liquid. The operation of
devices mat measure water conductivity are preferably based on measurement of liquid
resistivity between two electrodes. A device that measures current flow between at least
two electrodes can preferably be located on or within in a core tube of a reverse osmosis
filter device and/or system. Examples of such devices are disclosed in patents 3,867,688,
and 4,132,944, which are hereby incorporated in their entirety by reference. Electric
energy required to power such devices can be supplied by radio frequency radiation, a
rechargeable battery, power transferred from an RFID tag, electromagnetic energy, or
other forms of energy known to those skilled in the art.
The permeate conductivity measuring device of the preferred embodiments
consists of a conductivity cell which has an integrally mounted thermocouple. As shown
in Figure 13, the electrodes of the conductivity measuring device 170 are installed within
open shield 171 of the measuring device. When the conductivity cell is connected across
an a.c. sine wave excitation source, the resulting current is proportional to the cell
admittance. This current is resolved into two orthogonal components: a charging current
which leads the excitation voltage by 90° and is proportional to the dielectric constant (k)
of the liquid between the electrodes of the conductivity cell, and an ohmic current which
is in phase with the excitation voltage and is proportional to the reciprocal of the
resistance, or conductance, of the liquid.
Temperature compensation for the real component of the admittance
(conductance) can be based on the Arrhenius absolute rate model. Accordingly,
conductance is preferably a function of the thermal energy (RT), and the activation energy

AErh which separates equilibrium positions of the conducting species. The conductance G
at a process temperature T may be corrected to a conductance Go at the reference
temperature To by the equation:

The thermocouple embedded in the permeate conductivity measuring device
produces a signal proportional to the process liquid temperature T, while constant signals
analogous to the reference temperature T0 and to b are generated by appropriate circuitry.
These analog signals proportional to T, T0 and b, are combined to form a signal
representing the expression b(T0 -T). The log G function is generated from the signal
representative of the conductance G, added to the signal representing b (T0 -T), and sent
to an antilog amplifier, whose output signal is representative of the desired conductance
value G0 of the liquid.
The imaginary component of the admittance when divided by the excitation
frequency in radians per second is the capacitance C of the liquid at the processing
temperature T. Based on the simple volume expansion for the liquid and the Debye
model for dilute solutions of polar molecules, the temperature dependence of the
dielectric constant k of the liquid takes the form

as reported in the National Bureau of Standards circular 514. In terms of measured
capacitance,

where Co is the capacitance of the liquid at the reference temperature To, Ko is the
dielectric constant of the liquid at the reference temperature T0, a is the volume expansion
coefficient, and a = Α/KP.
This equation assumes that the capacitance C0 of the cell in air at the reference
temperature To is approximately equal to the capacitance C of the liquid at the measured

process temperature T divided by the dielectric constant k of the liquid at the process
temperature T. This assumption was made to allow the use of different conductivity cells
having different Co values, without changing any of the circuit values, and is accurate so
long as the dielectric constant variation with temperature is no more than plus or minus
ten percent, which is the case for water at the temperatures and pressures normally found
inRO filtration systems.
A signal proportional to a(To - T) is generated by the same method used to form
the b(To - T) term in the conductance compensation circuit. The signal proportional to the
capacitance C of the liquid and the signal proportional to a(T0 - T) are supplied to an
analog multiplier which generates a signal proportional to the product of these two
signals, aC(To - T). This product signal is then electrically subtracted from the
capacitance signal C to produce a signal proportional to the capacitance C0 of the liquid at
the reference temperature To.
For example, in one preferred embodiment of a permeate conductivity measuring
device, as shown in Figure 15, a quadrature oscillator 217 generates a 1000 Hz sine wave
voltage, which is amplified by an amplifier 218 and applied to a conductivity cell 219 of a
. liquid sensor probe immersed in the liquid being processed through shielded lines. The
current flowing through the conductivity cell 219 is converted into a proportional voltage
by a current transducer 222, and amplified by a narrow band amplifier 223. This
amplified voltage signal is men divided into two signals of opposite polarity by the phase
splitter 224, which are supplied to respective circuits of a first multiplier 225 and a second
multiplier 226.
In the first multiplier 225, the phase splitter output signals are preferably
multiplied by a square wave voltage signal generated by the quadrature oscillator 217
which is in phase with the voltage applied across the conductivity cell 219, to produce an
output signal proportional to the real component of the current flowing through the
conductivity cell 219, and thus proportional to the conductance G of the liquid.
In the second multiplier 226, the phase splitter signals are preferably multiplied by
a second square wave voltage signal, generated by the quadrature oscillator 217, winch is
90° out-of-phase with the voltage applied across the conductivity cell 219, to produce an
output signal proportional to the imaginary component of the current flowing through
liquid in the conductivity cell 219, and thus proportional to the capacitance C of the liquid
at its processing temperature T.

The liquid tensor probe also preferably includes a thermocouple 228 embedded in
it, which produces a signal proportional to the temperature of the liquid at the probe. This
temperature signal is amplified, and made linear with temperature in an amplifier and
compensation circuit 230.
In preferred embodiments, mis compensated temperature signal is directly
proportional to the liquid process temperature T, and is utilized in the temperature
compensation circuit of Figure 16, together with a signal proportional to the reference
temperature TOF to convert the signals proportional to the conductance G and the
capacitance C of the liquid at the measured temperature T to respective signals
proportional to the conductance G0 and the capacitance Co of the liquid at the reference
temperature To. In most applications of this monitoring apparatus, the reference
temperature T0 is selected to be about the average temperature of the liquid during the
processing operation, so mat temperature compensation is only made over the range from
the highest to the lowest temperature of the liquid during the processing operation.
In Figure 16, an amplifier is preferably used to produce a signal proportional to the
reference temperature T0, from which the signal proportional to the process liquid
temperature T can be electrically subtracted. An input of the amplifier 232 is connected
to a positive voltage source through the reference voltage resistor 234, and a feedback
resistor 236 is connected between the input and the output of the amplifier and is directly
proportional to the reference temperature T0, the value of the reference temperature
resistor 234 is inversely proportional to the reference temperature T0, and can be a
variable resistor, to allow selection of the reference temperature T0. Also, since the output
signal from the amplifier 232 must be equal to the output temperature signal from the
thermocouple amplifier at the selected temperature To, the value of the feedback resistor
236 is determined by the signal characteristics of the thermocouple amplifier 230.
Assuming the voltage output signal of the thermocouple amplifier 230 is 10 volts at
500°C, and varies with the temperature T at a rate of 0.02 volts per degree C, the output
voltage signal of the reference temperature amplifier 232 is preferably proportional to .02
(- T0) volts. Thus, if the positive voltage source is 15 volts, and the value of the
teno?erature resistance 234 is selected to equal 1/T0 x 107 ohms, the value of the feedback
resistor 236 is preferably approximately 13,300 ohms (13.3 K) to produce an output signal
of 0.02 (- T0) volts.

This 0.02 (- To) voltage signal is preferably supplied to an input of a gumming
amplifier 238 through a 10K resistor, and the 0.02 (T) voltage signal from the
thermocouple amplifier 230 is also supplied to the same input of the amplifier through
another 10K resistor 242. A 100K feedback resistor 244 is connected between the input
and the output of the amplifier 238, to produce an output temperature compensation signal
of 0.2 (T0 - T) volts, which is supplied to both the conductance and capacitance
compensation rircuits. When the measured liquid temperature T is equal to the reference
temperature Tw there will be no temperature compensation signal.
This 0.2 (T0 - T) temperature compensation signal is preferably supplied to an
input of the amplifier 246 through a conductance compensation resistor 248, having a
value of 1/b 102 ohms, which may be a variable resistor to allow this apparatus to be
used with different liquids having different "b" values. A 10K feedback resistor 250 is
preferably connected between its input and output The output of the amplifier 246,
representing 20b(To -T), is supplied to an input of the summing amplifier 2S2 through a
200K scaling resistor 254.
The output signal from the first multiplier 225, which is proportional to the liquid
conductance G, is preferably supplied to the input of a log amplifier 258 through a resistor
260. Assuming mat the maximum value of this conductance signal is + 5 volts full scale,
the resistor 260 can be selected to have an ohmic value of 50K, to thus allow a maximum
input current of 100µA to the log amplifier 258, and the log amplifier 258 may be selected
to have a transfer function of µ log (Amperes input current/100µA), so mat the voltage
output of the log amplifier 258 will preferably be - log G volts.
In preferred embodiments, this - log G signal is also supplied to the input of the
summing amplifier 252 through a 10K resistor 255, to produce an output signal of log G +
b (To -T) volts or log Go volts, since, as discussed earlier, log Gc - log G + b (To -T). This
log Go voltage signal is preferably supplied to an input of an amplifier 256 through a 10K
resistor 259, and a 10K feedback resistor 260 is connected between mis input and the
output of the amplifier 256, to invert the input signal and produce an output signal from
the amplifier 256 of - log G0 volts. This - log Go signal is then supplied to the input of
analog amplifier 262 having a transfer function of 10 x 10-x, where x is the input signal,
to produce an output signal of o to 10 volte that is directly proportional to the conductance
Go of the liquid.

In this permeate conductivity measuring device, the maximum value of the
capacitance signal from the second multiplier 226 is - 5 volte, and since a full scale
positive output of 10 volte proportional to the capacitance Q, of the liquid is desired, the
input signal from the second multiplier 226 is shown as - C/2 volts.
The 0.2 (T0 - T) volt temperature compensation signal from the amplifier 238 is
also supplied to an input of another amplifier 264 through a capacitance compensation
resistor 266, having an ohmic value of 1/a x 102. This capacitance compensation resistor
266 can be a variable resistor, which can be adjusted for use with different liquids having
different "a" values. A 5K amplifier feedback resistor 268 is preferably connected
between the input and the output of the other amplifier 264, to produce an output signal of
that amplifier of -10 [a (T0 - T)] volts, which is supplied to a first input of an analog
multiplier 270. The -C/2 volt signal from the second multiplier 226 is supplied to a
second input of the analog multiplier 270. The analog multiplier 270 has a transfer
function of one-tenth of the product of the two input signals, to produce an output signal
of a (To - T) C/2 volts. This output signal of the analog multiplier is supplied to an input
of a summing amplifier 272 through a 1 OK resistor 274. The -C/2 volt signal from the
second multiplier 226 is also supplied to the same input of the amplifier 272 through a
10K resistor 276. A 20K feedback resistor 278 is preferably connected between the input
and the output of the amplifier, to produce an output voltage signal proportional to C -
aC(To - T), or to the capacitance C of the liquid, since, as discussed earlier, Co = C -
aC(T0 - T).
m a preferred embodiment of a permeate conductivity measuring device, a
relatively high frequency of 1000 Hz is selected for the voltage applied across the
electrodes of the conductivity cell to reduce the effects of charge transfer kinetics
(Faradaic impedance) and electrode polarization, and to enhance the capacitive coupling
of the electrodes with the liquid (double layer capacitance). Also, the operational
amplifiers and other electronic components used in this embodiment are readily available
commercially at this operating frequency. However, the present disclosure is not limited
to devices employing this frequency, any frequency within an approximate range of 100
Hz to 107 Hz may be used. Also, the nominal operating temperature ranges maximum
deviation of the process temperature T from the reference temperature T0, and the
maximum absolute signal correction is preferably determined by the choice of circuit
components.

In another embodiment of a permeate conductivity measuring device, conductance
is measured by an electrodeleaa device. In such a device, noncontact measurement of the
conductance of the liquid is obtained by charging a capacitor in series with the primary
winding of a first transformer ring core. The capacitor is periodically discharged so that
across the primary winding, a damped oscillatory signal is produced as a result of the
capacitor, the inductance of the winding, and inherent resistivity. A loop including for at
least a portion of its path the liquid acts as a one-turn secondary winding for the first ring
core and as a one-turn primary winding for a second transformer ring core. At the instant
the discharge is initiated, a constant voltage appears across by loop regardless of the
resistance of Hie loop so that by measuring the peak current in a secondary winding of the
second core, which will appear at the initiation of discharge and which corresponds to the
current in me loop at the initiation of the discharge, the conductance of the liquid can be
determined using Ohm's law.
It should be appreciated that the conductivity measurement described above is not
limited to an assessment of the salinity of the liquid passing through the RO filtration
device, but may as easily be applied by those of skill in the art to the measurement of total
dissolved solids (TDS).
Additionally, it is not absolutely necessary that the conductance of the liquid be
obtained in order to measure salinity or TDS; other means known in the art, such as the
density method, or the refractance method, may be employed.
The system of this disclosure may be employed in the pressure vessel shown in
Figure 12. The pressure vessel is a cylindrical pipe 161 with number of membrane
elements 163 inside. The elements are connected to the end plates using adaptors 162 and
to each other through interconnectors 164. The pressure vessel has feed and concentrate
ports 165 & 166. Permeate leaves the pressure vessel through permeate ports 167. One
permeate port is closed with a cap 168. The pressure vessel could be a part of a pressure
vessel assembly (RO train), which may contain a large number of pressure vessels
connected in parallel. As shown in Figure 12, membrane elements are enclosed in a
pressure vessel, which operates under a pressure of 100 - 1200 psi. During operation of
the RO train the membrane elements are not accessible. Therefore, any complete
measurement of element performance has to be conducted by stopping the RO train,
removing elements from the pressure vessel and testing them individually in a separate

test unit. During operation it is possible to measure the conductivity of the combined
permeate from the pressure vessel. It is also possible to measure composite conductivity
along the pressure vessel by inserting a small-diameter probing tube through cap 168.
Samples of permeate collected at the other end of the probing tube correspond to specific
locations in the pressure vessel. However, conductivity results alone are not sufficient to
calculate element performance. To calculate element performance, the values of permeate
flow along the pressure vessel are required as well. The results of a measurement of
permeate flow, permeate conductivity and data of feed pressure, concentrate pressure,
feed salinity and temperature enable the calculation of normalized element performance.
There has been up to now no convenient way to measure permeate flow of individual
membrane elements while they are in operation in an RO unit
In an embodiment, an integrated sensor, shown in Figure 13, comprises a thermal
anemometer probe 169 and conductivity probe 170 mounted on a small diameter pipe and
protected by an open flow shield 171, As shown in Figure 14, to conduct measurement,
the integrated probe mounted on the supporting small diameter tube 173 is inserted
through a small opening in plug 168 into a permeate tube 172. The sensor is connected
via wiring to at least one recording device 174. In a preferred embodiment, the recording
device is an RFID tag attached to the individual reverse osmosis membrane element in
which the inlet side of the probing tube is located. Alternatively, the sensor can generate
a signal and send it wirelessly to the recording device. The opening in the plug 168 is
normally closed with a small diameter ball valve. Permeate leaves the pressure vessel
through the permeate port on the other end of the pressure vessel, which is connected to
the permeate manifold. This arrangement enables inserting the probe through the opening
of the valve during plant operation while assuring a minimal amount of permeate water
leaking outside during the flow and conductivity measurement process. The supporting
tubing, with the sensors mounted thereon, is progressively moved inside the connected
permeate tubes of the adjacent elements, and permeate flow and conductivity readings are
recorded and can be related to specific positions inside the length of the pressure vessel.
This may be accomplished in a variety of ways known in the art For example, the
sensors may transmit data to the closest RFID tag, which would be the tag associated with
the element in which the inlet side of the probe then resided. Alternatively,
electromagnetic radiation generated by a recording device located on a track outside the
pressure vessel could be used to serially activate the RFID tags of the individual elements,

which would then receive data from the season as the probe passed through each element.
Such communication would enable the measured values to be linked directly to the
individual element in which the sensors were located, which would facilitate die
determination of the performance of the individual elements. Alternatively, the measured
values could be linked to the individual elements by measuring the length to which die
support tubing was inserted into a pressure vessel.
The permeate flowing inside the connected permeate tubes of membrane elements
in me pressure vessel has an aggregate rate of permeate flow and permeate conductivity.
By talcing measurements along the length of connected permeate tubes, it is possible to
calculate the contribution of the permeate to the combined flow and conductivity at a
given point. The measured values, combined with historical data of the past performance
of an element, is important in determining the current condition of the elements in the
system. It also provides information required for the selection of elements that have to be
replaced to improve system performance.
Because conductivity of me permeate corresponding to specific locations in the
pressure vessel may be measured at the outlet end of the probing tube, it is not necessary
that conductivity be measured at the inlet end of the probing tube. In an embodiment, the
probing tube comprises only a mechanism for measuring permeate flow at the inlet end,
while permeate conductivity is measured at the outlet end.
Although all possible embodiments are not listed, the present disclosure
encompasses different embodiments that incorporate various changes, corrections and
modifications based on the knowledge of those skilled in the art. It should be clearly
understood mat the forms of the present disclosure are illustrative only and not intended
to limit the scope thereof. Modifications to these embodiments are also included in the
scope of the present disclosure, as long as they do not deviate from the spirit of the
disclosure.

1. A system that permits assessment of performance of a reverse osmosis
membrane element, comprising:
said reverse osmosis membrane element;
a permeate tube within said reverse osmosis membrane element;
an elongated probing tribe within the permeate tube of said reverse osmosis
membrane element;
at least one sensor configured to measure a value used to assess said
performance and disposed at an inlet side of said probing tube; and
a recording device in electronic communication with said sensor so as to
record results of said measurement.
2. The system of Claim 1, wherein said sensor configured to measure a value
used to assess said performance comprises a sensor for measuring permeate flow.
3. The system of-Claim 2, wherein said sensor for measuring permeate flow
comprises a thermal anemometer sensor.
4. The system of Claim 1, further comprising a sensor for measuring permeate
conductivity.
5. The system of Claim 4, wherein said sensor for measuring permeate
conductivity comprises a conductivity cell with an integrally mounted thermocouple.
6. The system of Claim 1, wherein a power source powers said sensor.
7. The system of Claim 6, wherein said power source comprises at least one radio
frequency identification (RFID) tag.
8. The system of Claim 1, wherein said electronic communication is conducted
via wiring connecting said recording device and said sensor.
9. The system of Claim 1, wherein said electronic communication is conducted
via a wireless connection connecting said recording device and said sensor.
10. The system of Claim 1, wherein said sensor is additionally provided with an
RFID tag, and said value is linked to a reverse osmosis membrane element via
communication between said RFID tag and an RFID tag mounted on said element.
11. A method of assessing performance of reverse osmosis membrane elements,
said method comprising:
a) providing a system in accordance with Claim 1 in a pressure vessel
containing at least one said element;

b) measuring at least one said value;
c) transmitting results of said measurement to said recording device; and
d) assessing said performance based on said results.

12. A method of assessing performance of reverse osmosis membrane elements in
accordance with Claim 11, wherein said at least one value comprises data relating to
permeate flow.
13. A method of assessing performance of reverse osmosis membrane elements in
accordance with Claim 12, wherein said at least one value additionally comprises data,
relating to permeate conductivity.
14. A method of assessing performance of reverse osmosis membrane elements in
acoordance with Claim 11, wherein said sensor is additionally provided with an RFIDtag,
and said value is linked to a reverse osmosis membrane element via communication
between said RFID tag and an RFID tag mounted on said element.
15. A method of assessing performance of reverse osmosis membrane elements in
accordance with Claim 11, additionally comprising:
e) replacing said element if said assessment indicates replacement is
required to improve system performance.

The present disclosure relates to a system comprising integrated sensors (169, 170) for measurement of permeate flow and permeate
conductivity of individual membrane elements (163) while the are in operation in an RO unit. The flow and conductivity measuring
integrated sensors (169, 170) are of a small size that enables them to be inserted into the permeate tube (172) of connected membrane
elements (163) during RO unit operation. Measured flow and conductivity information is transferred to the recording device (174)
through electric wires or through wireless transmission.