CA1245721A - Frazil ice concentration measuring apparatus - Google Patents
Frazil ice concentration measuring apparatusInfo
- Publication number
- CA1245721A CA1245721A CA000464700A CA464700A CA1245721A CA 1245721 A CA1245721 A CA 1245721A CA 000464700 A CA000464700 A CA 000464700A CA 464700 A CA464700 A CA 464700A CA 1245721 A CA1245721 A CA 1245721A
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- electrodes
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- ice
- temperature
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/22—Measuring resistance of fluids
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- General Physics & Mathematics (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A frazil ice concentration measuring instrument is described in which constant currents are supplied to a reference probe and sensor probe and used to generate voltages across the electrodes in these probes. The sensing and reference voltages are amplified and compared in signal processing circuitry to generate an output voltage which is then integrated to give an average value of frazil ice concentration in a given time. A
heating system using oil as the heat transfer medium is used to supply and maintain the electrodes of the sensing and reference probes just above freezing to prevent ice accumulation on the electrodes. The apparatus can also be used as general conductivity measuring instrument or for determining the concentration of a lesser conducting material in a more conducting liquid.
A frazil ice concentration measuring instrument is described in which constant currents are supplied to a reference probe and sensor probe and used to generate voltages across the electrodes in these probes. The sensing and reference voltages are amplified and compared in signal processing circuitry to generate an output voltage which is then integrated to give an average value of frazil ice concentration in a given time. A
heating system using oil as the heat transfer medium is used to supply and maintain the electrodes of the sensing and reference probes just above freezing to prevent ice accumulation on the electrodes. The apparatus can also be used as general conductivity measuring instrument or for determining the concentration of a lesser conducting material in a more conducting liquid.
Description
2~
FRAZIL, ICE CONCENTRATION MEASURING APPARTUS
The present invention relates to apparatus for measurlng the conductivity of a liquid and especially the concentration of a lesser conductive substance in a more conductive liquid. In particular, but not exclusively, the apparatus is suited to measure the concentration of frazil ice in fresh and saline water.
In turbulent water, whether in a flowing river or in the open sea, any ice formed is in the form of fine crystals suspended in water and is known as "frazil" ice. Depending on the degree of supercooling and the salinity of the water, the crystallographic shape and evolutin of frazil ice can vary. For fresh water under most natural conditions, however, the frazil ice is in the form of discoids that grow into dendritic crystals. As frazil ice crystals grow, agglomerate, pack and solldify, ice pans and flocs are produced which thicken as water continuously freezes to their undersides. The packing together of pans and flocs produces a continuous ice cover.
Frazil ice can greatly affect the flow properties of the water and it can also adhere to objects in the water to form anchor ice. In both cases the flow capacity of a water course can be substantially reduced and when, for example, frazil ice adheres to submerged water intake structures it often can completely block off the water intake and cause water supply or power production problems. The physical properties of frazil ice are ultimately determined by the structure of the crystals that constitute it. The crystal structure is determined by the thermal and hydrodynamic processes by which they are produced.
, ~ .
Knowledge of the formation, of the crystallographic evolution, and of the physical properties of frazil ice are also important for many northern industrial processes, such as the production of process water by desalination. In the Arctic region, a very feasible way to obtain process water is to draw water from the sea, produce frazil ice ln the saline water and then drain the brine and remelt the frazil ice to obtain low salinity process water. Knowledge of the formation and properties of saline frazil ice under different conditions could facilitate the development of an effective and efficient industrial desalination process. Also, in order to best utilize water resources during winter months, the properties and effect of frazil ice on water flow should be studied. This requires that a suitable instrument be constructed for the purposes of measuring the concentration of Erazil ice in water~
Pure water is well known to be of such high resistivity as to be electrically substantially non-conductive, and in fact its conductivity or resistivity is frequently used as a measure of its purity. However, natural water is more electrically conductive because of its mineral content. When water turns into ice, the impurities are rejected and remain in the ambient liquid because the orderly arrangement of molecules in ice crystals inhibits inclusion of these impurities therein.
Consequently, ice crystals are electrically much less conductive than the ambient liquid containing them. Therefore by measuring the change in the electrical conductivity of the water/frazil ice mixture because of the inclusion of the frazil ice, the amount of frazil ice in the mixture can be evaluated. Several techniques and apparatus for measuring the volume concentration of frazil ice have been proposed. Kristinsson, in a publication on an ice monitoring apparatus, Proc. IAH~, Symposium on Ice and its Action on Hydraulic Structures, Reyjavi~, Iceland, September 1970, reported constructing an instrument using the above principle in which two wires were spirally wound on an insulated rod which was immersed in frazil ice laden water. The resistance measured between the two wires was correlated with the concentration of frazil ice over the depth of the rod. This instrument was developed mainly empirically and it was difficult with it to correlate the resistance measurements with frazil ice concentration. Gilfilian, et al disclosed in a paper entitled:
"Ice formation in a small Alaskan stream, UNESCO-5; Properties and process of River and Lake Ice", published in 1972, that by measurin~ the conductivity changes o;E river water they were able to calculate the amount of ice formed in the river. Frazil ice has also been measured with apparatus based on calorific principles.
An instrument based on laser dopler phenomenon was developed by Schmidt & Glover, as reported in "A frazil ice concentration measuring sytem using a laser doppler velocimeter, Journ. of E~ydraulic Research, IAHR, Vol. 13, No. 3, 1975 pp.
229-314". The concentration of frazil ice and the velocity of the ice crystals were measured from the scattering of the laser beam by frazil ice crystals. This instrument was found to have a number of disadvantages because it was not only expensive and complex, but only gave accurate measurements at an early stage of ice formation, and even then, when the frazil ice concentration was low.
The principal object of the present invention is to provide a new frazil ice measuring instrument.
In the apparatus of the invention for measurement of the amount of frazil ice in water, this quantity is measured by providing a reference probe and sensing probe for insertion in the frazil ice/water mixtureO The reference probe contains or permits entrance of water without frazil ice while the sensing probe contains or allows the frazil ice-water mixture to flow through it. Each probe has two electrodes separated by its respective liquid and, in response to currents from a constant current source, reEerence and sensing voltages are measured between the separated electrodes respectively of the reEerence and sensing probes. The sensing and reference voltages are compared and processed to give an output signal which is proportional to the concentration of frazil ice in the water.
This signal can be processed to give an indication of the average concentration of the frazil ice. Preferably the electrodes of both the reference and sensing probes are heated to prevent buildup of frazil ice on the surface of the electrodes.
According to one aspect of the present invention there is provided apparatus for determining the concentratin of a lesser conductive substance in a more conductive liquid medium the apparatus comprising:
sensor means consisiting of sensor electrode means and reference electrode means, said sensor electrode means and said reference electrode means each having respective first and second electrically conductive electrodes spaced apart from one another which are inserted into the liquid medium, said llquid medium associated with said sensor electrode means having said lesser conductive substance therein, and said liquid medium associated with said reference electrode means being the same liquid medium without the lesser conductive substance therein;
power supply means for supplying respective reversible currents to said sensor electrode means and to said reference electrode means, said reversible currents flowing between respective first and second electrodes oE the sensor electrode means and the reference electrode means when said sensor means is immersed in said liquid medium;
voltage measuring means for measuring the respective voltages between said first and second electrodes of said sensor electrodes and said reference electrodes, and signal processing means for processing said measured voltages and for providing an output signal representative of the amount of said lesser conductive substance in the conductive liquid medium.
Preferably, the apparatus is used for determining the concentration of frazil ice in a frazil ice/fresh water or frazil ice/sea water mixture and the sensor electrode means is immersed in a frazil ice/water mixture which i5 between the two spaced electrodes there of and the reference electrode means is immersed in water free of frazil ice. when the apparatus is being used to measure frazil ice concentrations heating means are also provided for heating said first and second electrically conductive electrodes of the sensor and reference electrode means to prevent the accumulation of frazil ice on the surface ~2~s72~L
of these electrodes adjacent to the~~aterO
In a preferred embodiment of the invention the electric output signal from the sensor means is compared with an external reference voltage and the difference is integrated to give an average value of the differential voltage during the interval of integration. Thi5 averaged signal then gives the average concentration of frazil ice above a predetermined concentration which corresponds to the predetermined reference voltage~ In this way, the signals are counted and used to determine the ? average concentration of the frazil ice above any concentrative r level in the frazil ice/water mixture.
These and other aspects of the present invention will become apparent from the following description when taken in combination with the accompanying drawings in which:
Fig. 1 is a schematic block diagram of a frazil ice monitoring ice system for fresh water employing a preferred embodiment of the invention;
Fig. 2 is a side view of the sensor probe used in the system of Fig. 1 and showing the electrode housing and conduits for connecting the electrode housing to an oil reservoir and to associated signal processing and power supply apparatus;
Fig. 3 is a view of the probe of Fig. 2 taken in the direction of arrow "A" and showing the spacing between two sensor probe electrodes;
Fig. 4, is a circuit diagram of a constant current supply for the sensor and reference electrodes;
Fig. 5 is a circuit diagram of the current switching and the voltage signal processing shown schematically in Fig. l;
Fig. 6 (on same sheet as Fig. 4), is a circuit diagram of an integrating circuit used to integrate the output signal from the signal processing circuit shown in Fig. 5 and for determining the average value of the frazil ice concentration;
Fig. 7 is a diagrammatic view of heating apparatus used for maintaining the electrodes at a temperature just above 0 Celsius;
Fig. 8 is a circuit diagram of a circuit used to control the heating apparatus of Fig. 7 to maintain the electrodes at a predetermined temperature;
Fig~ 9 is a general wiring diagram of the apparatus.
Fig. 10 is a circuit diagram of a preamplifier and switching circuitry near the sensors used to measure frazil ice concentration in sea water;
Fig. 11 i9 a view of~ a probe similar to Figs. 2 and 3 showing the location of pre-amplifier circuitry in poximity to the sensors;
Fig. 12 is a more detailed and broken away view of the pre-amplifier housing shown in Fig. 11;
Fig. 13 is a general wiring diagram of the apparatus for use with fresh and sea water, and Fig. 14 is a diagrammatic view of a frazil ice sensor package assembly for measuring frazil ice concentration in sea water.
Reference is first made to Fig. 1 of the drawings which shows a schematic view of apparatus in accordance with a preferred embodiment of the invention. The apparatus comprises a probe, indicated generally by reference numeral 20 including a sensor probe and reEerence probe connected to probe power supplies 21, to signal processing and recording circuits generally indicated by reference numeral 22 and to sensor probe heating apparatus generally indicated by reference numeral 24.
The interrelation and operation of these elements will be described below.
The probe consists of a sensor probe 26, and a reference probe 28 which are adapted to be inserted into water where the frazil ice concentration is to be measured. The sensor and reference probes are identical and each probe has a pair of spaced electrode plates 32. In use the reference probe 28 is inserted in water which is free of frazil ice while the sensor probe 26 is inserted in a mixture of frazil ice and the water. Power is supplied to the sensor and reference probes from respective constant current sources 21. Each constant current source is adjustable as described below to provide the stable DC current. To avoid polarising the electrodes, t,he current between each pair of plates is inverted periodically or alternated in either direction and this is achieved by using solid state reversing switches controlled by an oscillating circuit, generally indicated by reference numeral 36. The voltage drops across the electrode plates of the sensor probe and reference probe are measured respectively between conductors 38 and between conductors 40 to give a sensing voltage Vs, and a reference voltage Vr respectively. These voltages are propor~ional to the resistivity of the liquid between the electrodes, the resistivity in the sensor probe being a function of the concentration by volume of the relatively non-conductive ~2~
frazil ice in the much more conductive liquid. The reference voltage and sensor voltage are processed in a voltage signal processing circuit generally indicated by reference numeral 42 to provide a voltage output signal which is a function of ratio of the resistance between the~electrodes of the sensor probe and the resistance between the electrodes of the reference probe.
This voltage output signal in normal use varies with time and can be applied to an external tape recorder or chart recorder for display and analysis. The analog output of the voltage processing circuit 42 can also be integrated in a difference integrator 44 to obtain the average analog signal.
The analog signal can also be compared with a signal from a reference voltage source 47 before integration. the reference voltage can be set to any desired threshold; only those levels of signal exceeding this threshold will be integrated and counted in a counter 48, and used to provide a signal representing average frazil ice concentration per unit volume above the pre-determined concentration corresponding to the reference voltage, as will be later explained.
Both the sensor probe and the reference probe require to be kept at a temperature slightly above freezing point of the liquid to prevent the deposition of fra il ice on the electrodes from the liquid contents, and this is achieved by a heating circuit generally indicated by the reference numeral 24. The heating medium is oil which is retained in an oil reservoir 5 and is heated by a heater 52. The heated oil is pumped by a discharge pump 53 through a delivery conduit 54 then through the reference probe 28 and the sensor probes 26 in paralleL, before g returning back to the oil reservoir 50 via return conduit 55.
The temperature of the return oil and the reservoir is measured by temperature sensors 57 and 58 respectively and the resultant temperature signals are compared in an oil heater power supply and control unit 56 with predetermined re~erence signals. The control unit 56 5uppl ies power to the heater 52 to maintain the temperature of the oil in the reservoir and that in the oil return conduit substantially constant.
The sensor probe 26 will now be described in greater j detail; it will be appreciated that because both probes are identical the parts described will correspond to like parts of the other probe. ~s seen in Figs. 2 and 3, the probe consists of two hollow shells, generally indicated by reference numeral 60, spaced apart and having flat inner surfaces 61 facing each other. The centre portion of each flat surface 61 iæ provided by a circular stainless steel electrode plate 62. The hollow shell is machined out of suitable plastic material to deEine a chamber 64 having its interior connected to the interiors of stainless steel conduits 66 and 68 for respectively delivering heating oil into and from the chamber 64. The two tubes 66 merge at their upper end into a common conduit 66a, while the two tubes 68 similarly merge into a common conduit 68a. The inlet conduit 66 also serves as a guide enclosing a conductor 67 for connection of the external circuits to the circular stainless steel plate 62. The shell is non-conductive either by using non-conductive material or by coating with an electrically non-conducting matrial. In this specific embodiment the outside diameter of the shell is about 8.5 centimeters (3-3/8"). The ~5~2~
heated oil is circulated through the chamber 64 by means of the stainless steel tubes 66 and 68, which are sealed to the shells to prevent leakage of oil into the water and vice versa. The oil is kept at a temperature sufficient to maintain the temperature of the electrode about 0 n 1 or 0.2 C above the freezing point of the liquid to prevent frazil ice from adhering to the electrode surface. The stainless steel tubes 66 and 68 also serve as a probe support and shields conductors 67 and 69 which connect the two spaced electrode plates 62 of the probe to an electrical connector 72 at the top of the probe, by which the probe can readily be connected and disconnected from the circuit. The circulation of the heating oil also prevents the formation of sheet ice on the support at the air/water interface. In this embodiment the diameter of the electrode plates 62 is 5 cm (2") and the plates are 5cm (2") apart, giving in this embodiment a sample volume of approximately 100 cm3 (6.25 in3). To avoid disturbing as much as possible smooth laminated flow of the liquid between the electrode surfaces 61, so as not to disturb the sample probe, the shells 60 forming the probe have edge surfaces 65 chamferred to be at an angle of 45 to the faces 61. The shells are also made as thin as possible and in this embodiment are about 1.6 cm (5/8") thick and are of overall length of about 1.25 m (4'). The probes and their supports are rigidly constructed and so as to stand the reasonably rugged use to which they are subjected in normal operation. The stainless steel tubes 66a and 68a, are mechanically held together by a clamp 70 to further rigidify the structure, the conductors 67 and 69 being taken out through ~s~
terminal connector 72 which is mechanically connected to the tube 66a as seen in Fig. 2. Conduits 66a and 68a are connectad to oil inlet conduit 54 and oil outlet conduit 55 respectively for delivering heating oil to the chamber 64 and removing it therefrom.
The reference probe must be immersed in a part of the ambient water that is as similar as possible in temperature and salinity, and is as free as possible from entrained frazil ice.
To this end advantage can be taken of the characteristic of the ice that its density is much lower than that of the water, so that it will always tend to float upward in the water. For example, the sample in which the reference electrode is immersed can be a portion that is diverted from the main stream into a chamber below the main stream, so that the ice tends not to enter it; the chamber can also be provided with openings in its upper part through which the ice will float upward back into the main stream. The passage of the main stream over these openings tending to suck the ice up out of the chamber back into the main stream. Again the reference electrode can be located at a place where the stream changes direction suddenly upwards and/or sideways when the less dense frazil ice will be concentrated in the outer longer-path part of the stream, leaving the inner shorter-path part substantially ice-free. The reference probe may al90 be placed in a shielded cage into which only water but not frazil ice can enter.
Reference is now made to Fig. 4 of the drawings which is a circuit diagram of constant current power supplies 78 and 76 respectively for the sensor probe 26 and the rsference probe .
28. Rach power supply consists of two operational amplifiers 80 and 82 for supply 76, and 84 and 86 for supply 78. Adjustment of respective potentiometers Pl and P2 permits the output currents from the two current sources to be adjustable within the range 3.5 to 4.5 milliamps, above in this preferred embodiment the currents normally being set to ~ (four) milliamps~ The range of variation of the constant currents can be increased from zero to 25 milliamps by changing the reference voltage supplies 92. The constant output currents from the constant current sources 76,78 pass through resistors R 43, R44 respectively which are used for current measurement purposes by measurement of the voltage drop across them.
Reference is now made to Fig. 5 which illustrates a circuit diagram of the voltage signal processing circuitry 42.
The constant curxent supply currents Ir and Is from current supplies 76 and 78 respectively are passed to solid state switches 94 and 96 respectively. These solid state switches are switched by an oscillator 97 at a rate of 1024 hertz with a transient time of switching of less than 10 6 seconds, so that the constant D.C. currents supplied by sources 7~ and 78 are fed to the probe electrodes as respective alternating currents of constant amplitudes. The oscillator 97 is o~ a stable crystal controlled type and gives a consistent frequency output. The potential differences across the reference probe electrodes and the sensor probe electrodes are used to provide the reference output voltage signal Vr and a sensor output voltage signal Vs on output leads 98 and 100 respec~ively, whi,ch are passed to respective inverting amplifiers 102, 104. Differential ~457~
amplifier 106 receives the outputs from inverting amplifiers 102, 104 and produces an output signal VO which is given by the following ~quation:
VO = 5-1 [(-Vs)-( Vr)] ~1) The output signal VO can be fed directly to a location on a test panel but it is also passed through a divider 108 which is necessary according to the theory of operation to avoid the effect of salinity and temperature on the output signal. The theory states that because, the reference voltage drop Vr is a function of the salinity and temperature of the water, while Vs is proportional to salinity, temperature and frazil ice concentration, so that the division of one by the other cancels the effects of salinity and temperature. It is found particularly important to reduce temperature effects as much as possible, since these can affect the measurements much more than the other parameters. The invertion of Vr and Vs is required because the denominator voltage signal applied to the divider 108 has to be negative. The divider output Vsig is given by the equation Vsig ~ 10 VO = 51.0 (Vs~vr) -~Vr Vr ~2) The divider output is then buffered by a buffer amplifier 110 to reduce the source impedence of the final output signal Vsig:
~ ~24~5~
In this embodiment the range of Vsi~ is 0 to 10 volts and can be fed directly to a display output or a chart recorder or the like or integrated to get an average signal value as described with reference to Fig. 1.
The salinity of naturally occurring waters varies over the range of 0-35 parts per thousand, fresh water usually being characterised as having less than 1 part (per thousand~ potable water as having about 1 to about 4 parts, brackish water as having from about 4 parts to about 10 parts, and usual seawaters i as having from about 18 to about 30 parts. The salinity of the - water at a given temperature is approximately linearly related to its conductivity and a standard salinity meter operating by measurement of conductivity has the following calibration (at 17~):
Salinity Conductivitv mMHOS/cm .. ~ .
O O
31 ~ ~0 With the probe embodiments described a fresh water such as tap water will result in a measurement of 400-500 ohms at the respective probe, while a saline water such as sea water will result in a measurement of about 5 ohms. The concentrations of the frazil ice normally measured are usually in the range of 0-10~ by volume. In the case of the fresh water measurement a 1~ concentration results in a measured change in resistance of 7~
about 4-S ohms, while the same concentration in sea water results in a measured change of only about 0.05 ohms. The crystal size of the ice varies widely and can in extreme cases be as much as 1 cm square.
Referring now to Fig. 9, panel zero, generally indicated by numeral 114, is provided with a precision potentiometer mounted on the test or front panel of the instrument and is used for initial zeroing of the signal outputs in both the reference probe and the sensor probe. The panel zero ad~ustment through amplifier 104 causes the output ~Vs of the amplifier 104 to be equal to the output ~Vr of the amplifier 102, and this thus makes the signal output Vsig at 112 from buffer ampLifier 110 equal to zero.
Reference i5 now made to Fig. 6, which shows the signal integration circuitry of this embodiment. In a subtractor 117, the output signal Vsig subtracts a reference signal Vref supplied from an external source. The output of the subtractor is fed to a voltage to frequency converter 118 which provides an output of 1000 hertz per volt input. The output 123 of the frequency converter is divided by a factor of 512 in a divider 120 and the output of the divider 120 is further processed using a monostable multivibrator 122 to provide a better recognisable recording signal by generating short pulses which are used to drive t-he event marker of a chart recorder (not shown) Using the integration circuitry described, for a given ti~e period, the total number N of short pulses marked by the event marker will be given by equation (3):
N= ~ (Vsi -Vref) l000dt (3) r 512 where voltage is in volts and time in secondsO It will be appreciated that the voltage to frequency converter 118 only works when the voltage is positive, or in other words only when the difference Vsig~Vref is greater than 0- Rearranging equation 3 gives $(Vsig-Vref)dt = 0.512N Volt-sec (4 When Vref is equal to zero, the above integration represents the area between the signal output curve and the zero voltage axis. The average value of VSi~-Vref in equation 4 may be expressed as follows:
V i -V = 0.512 N Volts (5) The integrating circuitry also permits the counting of pulses before the frequency divider using output line 123. In this case when the monitoring point is used the average Vsig-Vref value is given by equation:
Vsig~Vref 1000 Volts (6) ~ his signal represents the average concentraton o~
frazil ice passing between the electrodes of the sensor probe 26 in a predetermined time.
Reference will now be made to Figs. 7 and 8 to explain the operation of the oil heating apparatus 2~ illustrated thereby, using wherever possible ~he same references as are used in Fig. 1. As shown in Fig. 7, oil reservoir 50 is located in a reservoir container 126 which has insulated walls 128 and an insulated lid 130 which retains a top plate 132 and overlies a diaphragm 134. The reservoir container and pump and sensor are located in an enclosing housing 139. The heater 52 is connected by conductors via electrical connector 133 to the power supply in control unit 56. In this embodiment the reservoir has approximately 1 litre capacity and the heating oil is a silicone oil (Dow Corning 200). The warm oil in the reservoir 50 is pumped to the probes by a DC year pump 53 (Tuthill Pump Co., California, Model 9037) which has the advantage of providing additional flow control by varying the power input through the use of a rheostat or similar device. The temperature of the returning oil in the probes is sensed just before it returns to the reservoir by sensor 57 and the temperature signal sent to the control unit 56. If the returning oil temperature is less than the preset temperature (7C in this embodiment), the heater control will be activated and a current will be fed to the heater 52 to heat the oil in the reservoir. The temperature of the oil in the reservoir is also sensed by oil temperature sensor 58 and the respective temperature signal is again sent to the control box 56. If the oil temperature is hi~her than the preset maximum temperature limit (70~C in this embodiment), both the heater control and pump control will be activated to cut off currents to the heater and pump respectively. This provision prevents possible runaway heating and boiling of the oil in the case of pump failure. Flexible conduits 131 are used for conveyance of oil ~etween the housing 139 and the probes.
The heater control circuit of this e~bodiment is illustrated by circuit diagram Fig. 8 There are two modes of heater control, an automatic mode and a manual mode, and normally the automatic mode is used. The temperature sensing elements in temperature sensors 57 and 58 are provided by two diodes Dl and D2, the diode Dl senses the temperature in the reservoir and the diode D2 senses the temperature of the returning oil. The returning oil t~mperature signal from sensor 57 is ~mplified in amplifier 137 and i5 compared with a reference voltage set b~ adjusting potentiometer P7 of~
comparator 138. This reference voltage sets the desired returning oil temperature, i.e. (7C). The output of the comparator 138 is fed to another comparator 140, which controls the supply power to the heater through a series of transistor switches of which only Ql and Q2 are shown . As a safety measure, the reservoir or temperature signal produced by diode Dl in sensor 58 is amplified by amplifiers 136 and 144 and is then fed to a comparator 146. Should the temperature exceed 70C then a heater disable signal will be sent from the output of the comparator 146 to disconnect the heater 52 from its power supply.
In this emhodiment there is no automatic control for the pump 53 because it is turned on and off by the operator.
For the heater control to function automatically, the pump has to be on. Normally the heater is automatically controlled, and the heater control switch 147 (Fig. 93 on the front panel 156 is in the AUTO position. However, the switch could also be turned to the ON/OFF position by the operator and this manual operation overrides the automatic control.
' The apparatus has three power supplies; a f lSv DC
i power supply for all electronic circuits; a 16v DC power supply 152 for the pump 53 and a 100v DC power supply 154 for the heater 52. The general circuit wiring is illustrated in Fig.
9. The electronic circuit includes four electronic cards 150, the two transformer power supplies 152 and 154, the front test panel 156 and a recorder control circuit 15~ contained in an electronics box. The h~ater 52, pump S3 and temperature sensors 57 and 58 are contained in a separate box and connected to the electronic box by cables and connectors. Reservoir oil temperature and returning oil temperature can be measured using test points Tl and T~ respectively, on the front panel. A
recorded signal can also be fed into the front panel for integration. The "Int" terminal on the front panel is for direct frequency measurement from the voltage frequency connector which provides additional means to analyse the signal.
It will be appreciated that the instrument must be cabibrated before use and this is achieved by comparing measured concentrations with a theoretically calculated concentrations.
The measured concentration and theoretical concentration is for 7~L
different flow rates and is described in "Development and Calibration of the ~ Frazil Instrument by Gee Tsang and Manuel Pedrosa, Environmental Hydraulics Section, Hydraulics Division, National Water Research Institute, Canada Centre for Inland Waters, October 1983".
The high conductivity of sea water makes the voltage drop across the probes low relative to the voltage drops caused by lines and switches and this makes it difficult to obtain the ratio (Vs-Vr)/Vr with the circuitry shown in Figs. 1 - 9.
An alternative embodiment will now be described with reference to Figs. 10-13 which is suitable for measuring the concentration of frazil ice in sea water. Fig. 10 is a circuit diagram of the circuitry applied to the sensing probe and it will be appreciated that the reference probe has identical circuitry. In this circuit, switches 200 and 202 correspond to switch~s 94 and 96 in the first embodiment, and oscillator 204 replaces the crystal controLled oscillator and inverters lC2 (in Fig. 5), which are included in oscillator 204 to give outputs CL
and CL.
The signal from switches 200 and 202 is amplified in a pre-amplifier 206 to a comparable magnitude for further processing in the original cicuitry of Fig. 5, i.e. for amplifiers 102 and 104. To minimize the line resistance and line capactance effect on solid state switches 200 and 202 the pre-amplifier circuitry is located in a housing 208 close (about 6 inches) to the reference and sensing probes 210 and 212 as shown in Figs. 11 and 14. The housing has a cavity 214 (see Fig. 12) for containing the circuitry and is filled with oil at f~ i7~
r a constant temperature to ensure the stability of a circuit operation.
Fig. 12 shows the housing in more detail; the circuitry is mounted on a small printed circuit board 216 fixed to the inside of a plastic tubular enclosure 218 with watertight seals 219 located in the cavity 214. Oil flows around the enclosure 218 when returning ko the oil reservoir 50 from the probes.
The circuitry shown in Fig. 13 is similar to Fig. 9 but includes a terminal strip 220 (also shown in Fig. 10~. ~Jith this circuit the apparatus is capable of measuring the concentration of frazil ice in salt water and in fresh water.
When the instrument is to be used to measure fresh water, fresh water frazil probes are used, as shown in Figs 2 and 3, and use two jumpers Jl and J2 on terminal strip 220. The circuit of Fig. 13 is connected to measure ~resh water frazil ice concent:ration .
In order to measure the concentration oE frazil ice in sea water, the fresh water probes are replaced by the sea water probes and the jumpers Jl and J2 are removed. Tha complete apparatus for measuring the concentration of frazil ice in sea water is shown in Fig. 1~. The probes 210 and 212 are connected to a heater and pump box 222 which is in turn connected to the electronics house in a container 224.
Variou9 modifications may ~e made to the embodiment hereinbefore described without departing from the scope of the invention. For example, the design of the sensor and referen~e probes described is by way of example only and it will be appreciated that many different designs of probes could be :L~2~
utilized which fulfill ths same functions of providing a pair of electrodes defining a space between which liquid can be placed, and also having means for heating the ~lectrodes to maintain them above the temperature of the frazil ice/water mixture.
Also it will be appreciated that the principle of using conductivity measure~ent can be applied to determine the concentration of non-conducting particles in conducting liquids, and not necessarily at a liquid-solid phase change temperature so that there would be no requirement for heating the electrodes. In addition, although separate reference and sensor probes are shown, it will be appreciated that the electrodes can be combined into a signal probe with the sensor and reference electrodes partitioned, so that one pair of electrodes receives only frazil ice/water mixture or a mixture of the conducting medium and non-conducting material and the other electrode receiv~s the water or purely the conducting medium to act as the reference electrode. Also althouyh heating oil is used in this embodiment as the heating medium, this can be achieved by any heating fluid. In addition, although a single sensor probe was described it will be appreciated that several sensor probes could be used and the output voltage signals of the sensor probes multiplexed and averaged against a common reference probe. Such an arrangement would also work but would be more complex and costly than that disclosed in the present embodiment.
The invention has application in measuring the frazil ice content in the intake of cooling water for ships and the like, as well as for assessing the potency of waterways.
FRAZIL, ICE CONCENTRATION MEASURING APPARTUS
The present invention relates to apparatus for measurlng the conductivity of a liquid and especially the concentration of a lesser conductive substance in a more conductive liquid. In particular, but not exclusively, the apparatus is suited to measure the concentration of frazil ice in fresh and saline water.
In turbulent water, whether in a flowing river or in the open sea, any ice formed is in the form of fine crystals suspended in water and is known as "frazil" ice. Depending on the degree of supercooling and the salinity of the water, the crystallographic shape and evolutin of frazil ice can vary. For fresh water under most natural conditions, however, the frazil ice is in the form of discoids that grow into dendritic crystals. As frazil ice crystals grow, agglomerate, pack and solldify, ice pans and flocs are produced which thicken as water continuously freezes to their undersides. The packing together of pans and flocs produces a continuous ice cover.
Frazil ice can greatly affect the flow properties of the water and it can also adhere to objects in the water to form anchor ice. In both cases the flow capacity of a water course can be substantially reduced and when, for example, frazil ice adheres to submerged water intake structures it often can completely block off the water intake and cause water supply or power production problems. The physical properties of frazil ice are ultimately determined by the structure of the crystals that constitute it. The crystal structure is determined by the thermal and hydrodynamic processes by which they are produced.
, ~ .
Knowledge of the formation, of the crystallographic evolution, and of the physical properties of frazil ice are also important for many northern industrial processes, such as the production of process water by desalination. In the Arctic region, a very feasible way to obtain process water is to draw water from the sea, produce frazil ice ln the saline water and then drain the brine and remelt the frazil ice to obtain low salinity process water. Knowledge of the formation and properties of saline frazil ice under different conditions could facilitate the development of an effective and efficient industrial desalination process. Also, in order to best utilize water resources during winter months, the properties and effect of frazil ice on water flow should be studied. This requires that a suitable instrument be constructed for the purposes of measuring the concentration of Erazil ice in water~
Pure water is well known to be of such high resistivity as to be electrically substantially non-conductive, and in fact its conductivity or resistivity is frequently used as a measure of its purity. However, natural water is more electrically conductive because of its mineral content. When water turns into ice, the impurities are rejected and remain in the ambient liquid because the orderly arrangement of molecules in ice crystals inhibits inclusion of these impurities therein.
Consequently, ice crystals are electrically much less conductive than the ambient liquid containing them. Therefore by measuring the change in the electrical conductivity of the water/frazil ice mixture because of the inclusion of the frazil ice, the amount of frazil ice in the mixture can be evaluated. Several techniques and apparatus for measuring the volume concentration of frazil ice have been proposed. Kristinsson, in a publication on an ice monitoring apparatus, Proc. IAH~, Symposium on Ice and its Action on Hydraulic Structures, Reyjavi~, Iceland, September 1970, reported constructing an instrument using the above principle in which two wires were spirally wound on an insulated rod which was immersed in frazil ice laden water. The resistance measured between the two wires was correlated with the concentration of frazil ice over the depth of the rod. This instrument was developed mainly empirically and it was difficult with it to correlate the resistance measurements with frazil ice concentration. Gilfilian, et al disclosed in a paper entitled:
"Ice formation in a small Alaskan stream, UNESCO-5; Properties and process of River and Lake Ice", published in 1972, that by measurin~ the conductivity changes o;E river water they were able to calculate the amount of ice formed in the river. Frazil ice has also been measured with apparatus based on calorific principles.
An instrument based on laser dopler phenomenon was developed by Schmidt & Glover, as reported in "A frazil ice concentration measuring sytem using a laser doppler velocimeter, Journ. of E~ydraulic Research, IAHR, Vol. 13, No. 3, 1975 pp.
229-314". The concentration of frazil ice and the velocity of the ice crystals were measured from the scattering of the laser beam by frazil ice crystals. This instrument was found to have a number of disadvantages because it was not only expensive and complex, but only gave accurate measurements at an early stage of ice formation, and even then, when the frazil ice concentration was low.
The principal object of the present invention is to provide a new frazil ice measuring instrument.
In the apparatus of the invention for measurement of the amount of frazil ice in water, this quantity is measured by providing a reference probe and sensing probe for insertion in the frazil ice/water mixtureO The reference probe contains or permits entrance of water without frazil ice while the sensing probe contains or allows the frazil ice-water mixture to flow through it. Each probe has two electrodes separated by its respective liquid and, in response to currents from a constant current source, reEerence and sensing voltages are measured between the separated electrodes respectively of the reEerence and sensing probes. The sensing and reference voltages are compared and processed to give an output signal which is proportional to the concentration of frazil ice in the water.
This signal can be processed to give an indication of the average concentration of the frazil ice. Preferably the electrodes of both the reference and sensing probes are heated to prevent buildup of frazil ice on the surface of the electrodes.
According to one aspect of the present invention there is provided apparatus for determining the concentratin of a lesser conductive substance in a more conductive liquid medium the apparatus comprising:
sensor means consisiting of sensor electrode means and reference electrode means, said sensor electrode means and said reference electrode means each having respective first and second electrically conductive electrodes spaced apart from one another which are inserted into the liquid medium, said llquid medium associated with said sensor electrode means having said lesser conductive substance therein, and said liquid medium associated with said reference electrode means being the same liquid medium without the lesser conductive substance therein;
power supply means for supplying respective reversible currents to said sensor electrode means and to said reference electrode means, said reversible currents flowing between respective first and second electrodes oE the sensor electrode means and the reference electrode means when said sensor means is immersed in said liquid medium;
voltage measuring means for measuring the respective voltages between said first and second electrodes of said sensor electrodes and said reference electrodes, and signal processing means for processing said measured voltages and for providing an output signal representative of the amount of said lesser conductive substance in the conductive liquid medium.
Preferably, the apparatus is used for determining the concentration of frazil ice in a frazil ice/fresh water or frazil ice/sea water mixture and the sensor electrode means is immersed in a frazil ice/water mixture which i5 between the two spaced electrodes there of and the reference electrode means is immersed in water free of frazil ice. when the apparatus is being used to measure frazil ice concentrations heating means are also provided for heating said first and second electrically conductive electrodes of the sensor and reference electrode means to prevent the accumulation of frazil ice on the surface ~2~s72~L
of these electrodes adjacent to the~~aterO
In a preferred embodiment of the invention the electric output signal from the sensor means is compared with an external reference voltage and the difference is integrated to give an average value of the differential voltage during the interval of integration. Thi5 averaged signal then gives the average concentration of frazil ice above a predetermined concentration which corresponds to the predetermined reference voltage~ In this way, the signals are counted and used to determine the ? average concentration of the frazil ice above any concentrative r level in the frazil ice/water mixture.
These and other aspects of the present invention will become apparent from the following description when taken in combination with the accompanying drawings in which:
Fig. 1 is a schematic block diagram of a frazil ice monitoring ice system for fresh water employing a preferred embodiment of the invention;
Fig. 2 is a side view of the sensor probe used in the system of Fig. 1 and showing the electrode housing and conduits for connecting the electrode housing to an oil reservoir and to associated signal processing and power supply apparatus;
Fig. 3 is a view of the probe of Fig. 2 taken in the direction of arrow "A" and showing the spacing between two sensor probe electrodes;
Fig. 4, is a circuit diagram of a constant current supply for the sensor and reference electrodes;
Fig. 5 is a circuit diagram of the current switching and the voltage signal processing shown schematically in Fig. l;
Fig. 6 (on same sheet as Fig. 4), is a circuit diagram of an integrating circuit used to integrate the output signal from the signal processing circuit shown in Fig. 5 and for determining the average value of the frazil ice concentration;
Fig. 7 is a diagrammatic view of heating apparatus used for maintaining the electrodes at a temperature just above 0 Celsius;
Fig. 8 is a circuit diagram of a circuit used to control the heating apparatus of Fig. 7 to maintain the electrodes at a predetermined temperature;
Fig~ 9 is a general wiring diagram of the apparatus.
Fig. 10 is a circuit diagram of a preamplifier and switching circuitry near the sensors used to measure frazil ice concentration in sea water;
Fig. 11 i9 a view of~ a probe similar to Figs. 2 and 3 showing the location of pre-amplifier circuitry in poximity to the sensors;
Fig. 12 is a more detailed and broken away view of the pre-amplifier housing shown in Fig. 11;
Fig. 13 is a general wiring diagram of the apparatus for use with fresh and sea water, and Fig. 14 is a diagrammatic view of a frazil ice sensor package assembly for measuring frazil ice concentration in sea water.
Reference is first made to Fig. 1 of the drawings which shows a schematic view of apparatus in accordance with a preferred embodiment of the invention. The apparatus comprises a probe, indicated generally by reference numeral 20 including a sensor probe and reEerence probe connected to probe power supplies 21, to signal processing and recording circuits generally indicated by reference numeral 22 and to sensor probe heating apparatus generally indicated by reference numeral 24.
The interrelation and operation of these elements will be described below.
The probe consists of a sensor probe 26, and a reference probe 28 which are adapted to be inserted into water where the frazil ice concentration is to be measured. The sensor and reference probes are identical and each probe has a pair of spaced electrode plates 32. In use the reference probe 28 is inserted in water which is free of frazil ice while the sensor probe 26 is inserted in a mixture of frazil ice and the water. Power is supplied to the sensor and reference probes from respective constant current sources 21. Each constant current source is adjustable as described below to provide the stable DC current. To avoid polarising the electrodes, t,he current between each pair of plates is inverted periodically or alternated in either direction and this is achieved by using solid state reversing switches controlled by an oscillating circuit, generally indicated by reference numeral 36. The voltage drops across the electrode plates of the sensor probe and reference probe are measured respectively between conductors 38 and between conductors 40 to give a sensing voltage Vs, and a reference voltage Vr respectively. These voltages are propor~ional to the resistivity of the liquid between the electrodes, the resistivity in the sensor probe being a function of the concentration by volume of the relatively non-conductive ~2~
frazil ice in the much more conductive liquid. The reference voltage and sensor voltage are processed in a voltage signal processing circuit generally indicated by reference numeral 42 to provide a voltage output signal which is a function of ratio of the resistance between the~electrodes of the sensor probe and the resistance between the electrodes of the reference probe.
This voltage output signal in normal use varies with time and can be applied to an external tape recorder or chart recorder for display and analysis. The analog output of the voltage processing circuit 42 can also be integrated in a difference integrator 44 to obtain the average analog signal.
The analog signal can also be compared with a signal from a reference voltage source 47 before integration. the reference voltage can be set to any desired threshold; only those levels of signal exceeding this threshold will be integrated and counted in a counter 48, and used to provide a signal representing average frazil ice concentration per unit volume above the pre-determined concentration corresponding to the reference voltage, as will be later explained.
Both the sensor probe and the reference probe require to be kept at a temperature slightly above freezing point of the liquid to prevent the deposition of fra il ice on the electrodes from the liquid contents, and this is achieved by a heating circuit generally indicated by the reference numeral 24. The heating medium is oil which is retained in an oil reservoir 5 and is heated by a heater 52. The heated oil is pumped by a discharge pump 53 through a delivery conduit 54 then through the reference probe 28 and the sensor probes 26 in paralleL, before g returning back to the oil reservoir 50 via return conduit 55.
The temperature of the return oil and the reservoir is measured by temperature sensors 57 and 58 respectively and the resultant temperature signals are compared in an oil heater power supply and control unit 56 with predetermined re~erence signals. The control unit 56 5uppl ies power to the heater 52 to maintain the temperature of the oil in the reservoir and that in the oil return conduit substantially constant.
The sensor probe 26 will now be described in greater j detail; it will be appreciated that because both probes are identical the parts described will correspond to like parts of the other probe. ~s seen in Figs. 2 and 3, the probe consists of two hollow shells, generally indicated by reference numeral 60, spaced apart and having flat inner surfaces 61 facing each other. The centre portion of each flat surface 61 iæ provided by a circular stainless steel electrode plate 62. The hollow shell is machined out of suitable plastic material to deEine a chamber 64 having its interior connected to the interiors of stainless steel conduits 66 and 68 for respectively delivering heating oil into and from the chamber 64. The two tubes 66 merge at their upper end into a common conduit 66a, while the two tubes 68 similarly merge into a common conduit 68a. The inlet conduit 66 also serves as a guide enclosing a conductor 67 for connection of the external circuits to the circular stainless steel plate 62. The shell is non-conductive either by using non-conductive material or by coating with an electrically non-conducting matrial. In this specific embodiment the outside diameter of the shell is about 8.5 centimeters (3-3/8"). The ~5~2~
heated oil is circulated through the chamber 64 by means of the stainless steel tubes 66 and 68, which are sealed to the shells to prevent leakage of oil into the water and vice versa. The oil is kept at a temperature sufficient to maintain the temperature of the electrode about 0 n 1 or 0.2 C above the freezing point of the liquid to prevent frazil ice from adhering to the electrode surface. The stainless steel tubes 66 and 68 also serve as a probe support and shields conductors 67 and 69 which connect the two spaced electrode plates 62 of the probe to an electrical connector 72 at the top of the probe, by which the probe can readily be connected and disconnected from the circuit. The circulation of the heating oil also prevents the formation of sheet ice on the support at the air/water interface. In this embodiment the diameter of the electrode plates 62 is 5 cm (2") and the plates are 5cm (2") apart, giving in this embodiment a sample volume of approximately 100 cm3 (6.25 in3). To avoid disturbing as much as possible smooth laminated flow of the liquid between the electrode surfaces 61, so as not to disturb the sample probe, the shells 60 forming the probe have edge surfaces 65 chamferred to be at an angle of 45 to the faces 61. The shells are also made as thin as possible and in this embodiment are about 1.6 cm (5/8") thick and are of overall length of about 1.25 m (4'). The probes and their supports are rigidly constructed and so as to stand the reasonably rugged use to which they are subjected in normal operation. The stainless steel tubes 66a and 68a, are mechanically held together by a clamp 70 to further rigidify the structure, the conductors 67 and 69 being taken out through ~s~
terminal connector 72 which is mechanically connected to the tube 66a as seen in Fig. 2. Conduits 66a and 68a are connectad to oil inlet conduit 54 and oil outlet conduit 55 respectively for delivering heating oil to the chamber 64 and removing it therefrom.
The reference probe must be immersed in a part of the ambient water that is as similar as possible in temperature and salinity, and is as free as possible from entrained frazil ice.
To this end advantage can be taken of the characteristic of the ice that its density is much lower than that of the water, so that it will always tend to float upward in the water. For example, the sample in which the reference electrode is immersed can be a portion that is diverted from the main stream into a chamber below the main stream, so that the ice tends not to enter it; the chamber can also be provided with openings in its upper part through which the ice will float upward back into the main stream. The passage of the main stream over these openings tending to suck the ice up out of the chamber back into the main stream. Again the reference electrode can be located at a place where the stream changes direction suddenly upwards and/or sideways when the less dense frazil ice will be concentrated in the outer longer-path part of the stream, leaving the inner shorter-path part substantially ice-free. The reference probe may al90 be placed in a shielded cage into which only water but not frazil ice can enter.
Reference is now made to Fig. 4 of the drawings which is a circuit diagram of constant current power supplies 78 and 76 respectively for the sensor probe 26 and the rsference probe .
28. Rach power supply consists of two operational amplifiers 80 and 82 for supply 76, and 84 and 86 for supply 78. Adjustment of respective potentiometers Pl and P2 permits the output currents from the two current sources to be adjustable within the range 3.5 to 4.5 milliamps, above in this preferred embodiment the currents normally being set to ~ (four) milliamps~ The range of variation of the constant currents can be increased from zero to 25 milliamps by changing the reference voltage supplies 92. The constant output currents from the constant current sources 76,78 pass through resistors R 43, R44 respectively which are used for current measurement purposes by measurement of the voltage drop across them.
Reference is now made to Fig. 5 which illustrates a circuit diagram of the voltage signal processing circuitry 42.
The constant curxent supply currents Ir and Is from current supplies 76 and 78 respectively are passed to solid state switches 94 and 96 respectively. These solid state switches are switched by an oscillator 97 at a rate of 1024 hertz with a transient time of switching of less than 10 6 seconds, so that the constant D.C. currents supplied by sources 7~ and 78 are fed to the probe electrodes as respective alternating currents of constant amplitudes. The oscillator 97 is o~ a stable crystal controlled type and gives a consistent frequency output. The potential differences across the reference probe electrodes and the sensor probe electrodes are used to provide the reference output voltage signal Vr and a sensor output voltage signal Vs on output leads 98 and 100 respec~ively, whi,ch are passed to respective inverting amplifiers 102, 104. Differential ~457~
amplifier 106 receives the outputs from inverting amplifiers 102, 104 and produces an output signal VO which is given by the following ~quation:
VO = 5-1 [(-Vs)-( Vr)] ~1) The output signal VO can be fed directly to a location on a test panel but it is also passed through a divider 108 which is necessary according to the theory of operation to avoid the effect of salinity and temperature on the output signal. The theory states that because, the reference voltage drop Vr is a function of the salinity and temperature of the water, while Vs is proportional to salinity, temperature and frazil ice concentration, so that the division of one by the other cancels the effects of salinity and temperature. It is found particularly important to reduce temperature effects as much as possible, since these can affect the measurements much more than the other parameters. The invertion of Vr and Vs is required because the denominator voltage signal applied to the divider 108 has to be negative. The divider output Vsig is given by the equation Vsig ~ 10 VO = 51.0 (Vs~vr) -~Vr Vr ~2) The divider output is then buffered by a buffer amplifier 110 to reduce the source impedence of the final output signal Vsig:
~ ~24~5~
In this embodiment the range of Vsi~ is 0 to 10 volts and can be fed directly to a display output or a chart recorder or the like or integrated to get an average signal value as described with reference to Fig. 1.
The salinity of naturally occurring waters varies over the range of 0-35 parts per thousand, fresh water usually being characterised as having less than 1 part (per thousand~ potable water as having about 1 to about 4 parts, brackish water as having from about 4 parts to about 10 parts, and usual seawaters i as having from about 18 to about 30 parts. The salinity of the - water at a given temperature is approximately linearly related to its conductivity and a standard salinity meter operating by measurement of conductivity has the following calibration (at 17~):
Salinity Conductivitv mMHOS/cm .. ~ .
O O
31 ~ ~0 With the probe embodiments described a fresh water such as tap water will result in a measurement of 400-500 ohms at the respective probe, while a saline water such as sea water will result in a measurement of about 5 ohms. The concentrations of the frazil ice normally measured are usually in the range of 0-10~ by volume. In the case of the fresh water measurement a 1~ concentration results in a measured change in resistance of 7~
about 4-S ohms, while the same concentration in sea water results in a measured change of only about 0.05 ohms. The crystal size of the ice varies widely and can in extreme cases be as much as 1 cm square.
Referring now to Fig. 9, panel zero, generally indicated by numeral 114, is provided with a precision potentiometer mounted on the test or front panel of the instrument and is used for initial zeroing of the signal outputs in both the reference probe and the sensor probe. The panel zero ad~ustment through amplifier 104 causes the output ~Vs of the amplifier 104 to be equal to the output ~Vr of the amplifier 102, and this thus makes the signal output Vsig at 112 from buffer ampLifier 110 equal to zero.
Reference i5 now made to Fig. 6, which shows the signal integration circuitry of this embodiment. In a subtractor 117, the output signal Vsig subtracts a reference signal Vref supplied from an external source. The output of the subtractor is fed to a voltage to frequency converter 118 which provides an output of 1000 hertz per volt input. The output 123 of the frequency converter is divided by a factor of 512 in a divider 120 and the output of the divider 120 is further processed using a monostable multivibrator 122 to provide a better recognisable recording signal by generating short pulses which are used to drive t-he event marker of a chart recorder (not shown) Using the integration circuitry described, for a given ti~e period, the total number N of short pulses marked by the event marker will be given by equation (3):
N= ~ (Vsi -Vref) l000dt (3) r 512 where voltage is in volts and time in secondsO It will be appreciated that the voltage to frequency converter 118 only works when the voltage is positive, or in other words only when the difference Vsig~Vref is greater than 0- Rearranging equation 3 gives $(Vsig-Vref)dt = 0.512N Volt-sec (4 When Vref is equal to zero, the above integration represents the area between the signal output curve and the zero voltage axis. The average value of VSi~-Vref in equation 4 may be expressed as follows:
V i -V = 0.512 N Volts (5) The integrating circuitry also permits the counting of pulses before the frequency divider using output line 123. In this case when the monitoring point is used the average Vsig-Vref value is given by equation:
Vsig~Vref 1000 Volts (6) ~ his signal represents the average concentraton o~
frazil ice passing between the electrodes of the sensor probe 26 in a predetermined time.
Reference will now be made to Figs. 7 and 8 to explain the operation of the oil heating apparatus 2~ illustrated thereby, using wherever possible ~he same references as are used in Fig. 1. As shown in Fig. 7, oil reservoir 50 is located in a reservoir container 126 which has insulated walls 128 and an insulated lid 130 which retains a top plate 132 and overlies a diaphragm 134. The reservoir container and pump and sensor are located in an enclosing housing 139. The heater 52 is connected by conductors via electrical connector 133 to the power supply in control unit 56. In this embodiment the reservoir has approximately 1 litre capacity and the heating oil is a silicone oil (Dow Corning 200). The warm oil in the reservoir 50 is pumped to the probes by a DC year pump 53 (Tuthill Pump Co., California, Model 9037) which has the advantage of providing additional flow control by varying the power input through the use of a rheostat or similar device. The temperature of the returning oil in the probes is sensed just before it returns to the reservoir by sensor 57 and the temperature signal sent to the control unit 56. If the returning oil temperature is less than the preset temperature (7C in this embodiment), the heater control will be activated and a current will be fed to the heater 52 to heat the oil in the reservoir. The temperature of the oil in the reservoir is also sensed by oil temperature sensor 58 and the respective temperature signal is again sent to the control box 56. If the oil temperature is hi~her than the preset maximum temperature limit (70~C in this embodiment), both the heater control and pump control will be activated to cut off currents to the heater and pump respectively. This provision prevents possible runaway heating and boiling of the oil in the case of pump failure. Flexible conduits 131 are used for conveyance of oil ~etween the housing 139 and the probes.
The heater control circuit of this e~bodiment is illustrated by circuit diagram Fig. 8 There are two modes of heater control, an automatic mode and a manual mode, and normally the automatic mode is used. The temperature sensing elements in temperature sensors 57 and 58 are provided by two diodes Dl and D2, the diode Dl senses the temperature in the reservoir and the diode D2 senses the temperature of the returning oil. The returning oil t~mperature signal from sensor 57 is ~mplified in amplifier 137 and i5 compared with a reference voltage set b~ adjusting potentiometer P7 of~
comparator 138. This reference voltage sets the desired returning oil temperature, i.e. (7C). The output of the comparator 138 is fed to another comparator 140, which controls the supply power to the heater through a series of transistor switches of which only Ql and Q2 are shown . As a safety measure, the reservoir or temperature signal produced by diode Dl in sensor 58 is amplified by amplifiers 136 and 144 and is then fed to a comparator 146. Should the temperature exceed 70C then a heater disable signal will be sent from the output of the comparator 146 to disconnect the heater 52 from its power supply.
In this emhodiment there is no automatic control for the pump 53 because it is turned on and off by the operator.
For the heater control to function automatically, the pump has to be on. Normally the heater is automatically controlled, and the heater control switch 147 (Fig. 93 on the front panel 156 is in the AUTO position. However, the switch could also be turned to the ON/OFF position by the operator and this manual operation overrides the automatic control.
' The apparatus has three power supplies; a f lSv DC
i power supply for all electronic circuits; a 16v DC power supply 152 for the pump 53 and a 100v DC power supply 154 for the heater 52. The general circuit wiring is illustrated in Fig.
9. The electronic circuit includes four electronic cards 150, the two transformer power supplies 152 and 154, the front test panel 156 and a recorder control circuit 15~ contained in an electronics box. The h~ater 52, pump S3 and temperature sensors 57 and 58 are contained in a separate box and connected to the electronic box by cables and connectors. Reservoir oil temperature and returning oil temperature can be measured using test points Tl and T~ respectively, on the front panel. A
recorded signal can also be fed into the front panel for integration. The "Int" terminal on the front panel is for direct frequency measurement from the voltage frequency connector which provides additional means to analyse the signal.
It will be appreciated that the instrument must be cabibrated before use and this is achieved by comparing measured concentrations with a theoretically calculated concentrations.
The measured concentration and theoretical concentration is for 7~L
different flow rates and is described in "Development and Calibration of the ~ Frazil Instrument by Gee Tsang and Manuel Pedrosa, Environmental Hydraulics Section, Hydraulics Division, National Water Research Institute, Canada Centre for Inland Waters, October 1983".
The high conductivity of sea water makes the voltage drop across the probes low relative to the voltage drops caused by lines and switches and this makes it difficult to obtain the ratio (Vs-Vr)/Vr with the circuitry shown in Figs. 1 - 9.
An alternative embodiment will now be described with reference to Figs. 10-13 which is suitable for measuring the concentration of frazil ice in sea water. Fig. 10 is a circuit diagram of the circuitry applied to the sensing probe and it will be appreciated that the reference probe has identical circuitry. In this circuit, switches 200 and 202 correspond to switch~s 94 and 96 in the first embodiment, and oscillator 204 replaces the crystal controLled oscillator and inverters lC2 (in Fig. 5), which are included in oscillator 204 to give outputs CL
and CL.
The signal from switches 200 and 202 is amplified in a pre-amplifier 206 to a comparable magnitude for further processing in the original cicuitry of Fig. 5, i.e. for amplifiers 102 and 104. To minimize the line resistance and line capactance effect on solid state switches 200 and 202 the pre-amplifier circuitry is located in a housing 208 close (about 6 inches) to the reference and sensing probes 210 and 212 as shown in Figs. 11 and 14. The housing has a cavity 214 (see Fig. 12) for containing the circuitry and is filled with oil at f~ i7~
r a constant temperature to ensure the stability of a circuit operation.
Fig. 12 shows the housing in more detail; the circuitry is mounted on a small printed circuit board 216 fixed to the inside of a plastic tubular enclosure 218 with watertight seals 219 located in the cavity 214. Oil flows around the enclosure 218 when returning ko the oil reservoir 50 from the probes.
The circuitry shown in Fig. 13 is similar to Fig. 9 but includes a terminal strip 220 (also shown in Fig. 10~. ~Jith this circuit the apparatus is capable of measuring the concentration of frazil ice in salt water and in fresh water.
When the instrument is to be used to measure fresh water, fresh water frazil probes are used, as shown in Figs 2 and 3, and use two jumpers Jl and J2 on terminal strip 220. The circuit of Fig. 13 is connected to measure ~resh water frazil ice concent:ration .
In order to measure the concentration oE frazil ice in sea water, the fresh water probes are replaced by the sea water probes and the jumpers Jl and J2 are removed. Tha complete apparatus for measuring the concentration of frazil ice in sea water is shown in Fig. 1~. The probes 210 and 212 are connected to a heater and pump box 222 which is in turn connected to the electronics house in a container 224.
Variou9 modifications may ~e made to the embodiment hereinbefore described without departing from the scope of the invention. For example, the design of the sensor and referen~e probes described is by way of example only and it will be appreciated that many different designs of probes could be :L~2~
utilized which fulfill ths same functions of providing a pair of electrodes defining a space between which liquid can be placed, and also having means for heating the ~lectrodes to maintain them above the temperature of the frazil ice/water mixture.
Also it will be appreciated that the principle of using conductivity measure~ent can be applied to determine the concentration of non-conducting particles in conducting liquids, and not necessarily at a liquid-solid phase change temperature so that there would be no requirement for heating the electrodes. In addition, although separate reference and sensor probes are shown, it will be appreciated that the electrodes can be combined into a signal probe with the sensor and reference electrodes partitioned, so that one pair of electrodes receives only frazil ice/water mixture or a mixture of the conducting medium and non-conducting material and the other electrode receiv~s the water or purely the conducting medium to act as the reference electrode. Also althouyh heating oil is used in this embodiment as the heating medium, this can be achieved by any heating fluid. In addition, although a single sensor probe was described it will be appreciated that several sensor probes could be used and the output voltage signals of the sensor probes multiplexed and averaged against a common reference probe. Such an arrangement would also work but would be more complex and costly than that disclosed in the present embodiment.
The invention has application in measuring the frazil ice content in the intake of cooling water for ships and the like, as well as for assessing the potency of waterways.
Claims (15)
1. Apparatus for determining the amount of a lesser conductive substance in a more conductive liquid medium comprising:
sensor means consisiting of sensor electrode means and reference electrode means, said sensor electrode means and said reference electrode means each having respective first and second electrically conductive electrodes spaced apart from one another which are inserted into the liquid medium, said liquid medium associated with said sensor electrode means having said lesser conductive substance therein, and said liquid medium associated with said reference electrode means being the same liquid medium without the lesser conductive substance therein;
power supply means for supplying respective reversible currents to said sensor electrode means and to said reference electrode means, said reversible currents flowing between respective first and second electrodes of the sensor electrode means and the reference electrode means when said sensor means is immersed in said liquid medium;
voltage measuring means for measuring the respective voltages between said first and second electrodes of said sensor electrodes and said reference electrodes, and signal processing means for processing said measured voltages and for providing an output signal representative of the amount of said lesser conductive substance in the conductive liquid medium.
sensor means consisiting of sensor electrode means and reference electrode means, said sensor electrode means and said reference electrode means each having respective first and second electrically conductive electrodes spaced apart from one another which are inserted into the liquid medium, said liquid medium associated with said sensor electrode means having said lesser conductive substance therein, and said liquid medium associated with said reference electrode means being the same liquid medium without the lesser conductive substance therein;
power supply means for supplying respective reversible currents to said sensor electrode means and to said reference electrode means, said reversible currents flowing between respective first and second electrodes of the sensor electrode means and the reference electrode means when said sensor means is immersed in said liquid medium;
voltage measuring means for measuring the respective voltages between said first and second electrodes of said sensor electrodes and said reference electrodes, and signal processing means for processing said measured voltages and for providing an output signal representative of the amount of said lesser conductive substance in the conductive liquid medium.
2. Apparatus as claimed in claim 1, where said liquid medium is water and said substantially non-conducting substance is frazil ice, said apparatus including heating means for heating and maintaining said first and second electrically conductive electrodes at a temperature sufficient to prevent frazil ice from adhering to the surface of the electrodes.
3. Apparatus as claimed in claim 2, wherein the heating means comprises container means containing a reservoir of oil to be heated for heating said first and second electrically conductive electrodes, supply and return conduit means for connecting said reservoir to said electrodes, pump means for recirculating said heating means from said reservoir through said electrodes and back to said reservoir, temperature sensor means for sensing the temperature of the oil reservoir and the temperature of the oil in the return conduit means, and heating power supply and control means response to the temperature signals for controlling the switching of said heater to maintain the oil at a temperature sufficient to prevent frazil ice adhering to the surface of said electrodes.
4. Apparatus as claimed in any one of claims 1 to 3, wherein said signal processing means includes integrating means for integrating said measured voltages, said integrating means having subtraction means for subtracting a predetermined reference voltage from the measured voltages to generate a difference signal, and voltage to frequency conversion means for generating a number of pulses proportional to said voltage difference in a predetermined time, and pulse processing means for processing said pulses to give an average output value of the difference signal, said average output value being proportional to the frazil ice concentration.
5. Apparatus as claimed in any one of claims 1 to 3, wherein said current supply means consists of a constant current supply for said sensor electrode means and a separate constant current supply for said reference electrode means, and solid state switching means associated with each constant current supply for reversing the current from said constant current supply and applying the respective reversing current across the electrodes of the respective sensor means.
6. Apparatus as claimed in any one of claims 1 to 3, wherein said signal processing means includes integrating means for integrating said measured voltages, said integrating means having subtraction means for subtracting a predetermined reference voltage from the measured voltages to generate a difference signal, and voltage to frequency conversion means for generating a number of pulses proportional to said voltage difference in a predetermined time, and pulse processing means for processing said pulses to give an average output value of the difference signal, said average output value being proportional to the frazil ice concentration.
7. Apparatus as claimed in any one of claims 1 to 3, wherein said current supply means consists of a constant current supply for said sensor electrode means and a separate constant current supply for said reference electrode means, and solid state switching means associated with each constant current supply for reversing the current from said constant current supply and applying the respective reversing current across the electrodes of the respective sensor means.
8. Apparatus as claimed in claim 2, wherein the conductive medium is sea water and pre-amplifier means for amplifying the measured signal are located in proximity to the sensor means, said amplifier means being located in a sealed unit in a housing which is connected in line in said oil return conduit to maintain the temperature of said pre-amplifier means substantially constant.
9. Apparatus as claimed in any one of claims 1 to 3 and comprising separate sensor means for measuring the concentration of frazil ice in sea water and fresh water interchangeably connectable in said apparatus.
10. Apparatus as claimed in claim 3, wherein the conductive medium is sea water and pre-amplifier means for amplifying the measured signal are located in proximity to the sensor means, said amplifier means being located in a sealed unit in a housing which is connected in line in said oil return conduit to maintain the temperature of said pre-amplifier means substantially constant.
11. Apparatus as claimed in any one of claims 1 to 3, wherein the sensor probe spaced electrodes define a volume for receiving a mixture of said lesser conductive substances and said conductive liquid medium, and the reference probe spaced electrodes define a volume for receiving said liquid medium without the lesser conductive substance, each electrode comprising a housing and having a surface for contacting said respective media, each housing having means for connecting an electrical conductor between said electrode and said apparatus.
12. Apparatus as claimed in any one of claims 1 to 3, wherein each electrode comprises a housing, each housing defines a chamber, and each chamber has a wall portion formed by the electrode, the apparatus comprising conduit means connected to the chamber for connecting the interior of said chamber to a heating means, said heating means delivering by conduit means heating fluid to said chamber to maintain the temperature of said electrodes at a predetermined value.
13. Apparatus as claimed in any one of claims 1 to 3, wherein each electrode comprises a housing, the housing of the sensor probe and the reference probe each being discoid in shape and having a surface angled away from the respective volume between the pair of electrodes.
14. Apparatus as claimed in any one of claims 1 to 3, wherein said electrodes are circular metal discs.
15. Apparatus as claimed in any one of claims 1 to 3, and for measuring the concentration of frazil ice in sea water, the sensor probe spaced electrodes bounding a volume for receiving a mixture of said frazil ice and sea water and the reference probe spaced electrodes bounding a volume for receiving sea water without said frazil ice, each electrode comprising a housing and having a surface for contacting the respective medium, each housing having means for connecting an electrical conductor between said electrode and said apparatus, each housing defining a chamber and, each chamber having a wall portion formed by said electrode, conduit means connected to the chamber for connecting the interior of said chamber to a heating means, said heating means delivering by conduit means heating fluid to said chamber to maintain the temperature of said electrodes at a paredetermined value, pre-amplifier means located in proximity to said electrodes for amplifying the measured signal;
said pre-amplifier means being located in a sealed unit in a housing located in-line in one of said conduits to maintain the temperature of the pre-amplifier means substantially constant.
said pre-amplifier means being located in a sealed unit in a housing located in-line in one of said conduits to maintain the temperature of the pre-amplifier means substantially constant.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000464700A CA1245721A (en) | 1984-10-03 | 1984-10-03 | Frazil ice concentration measuring apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000464700A CA1245721A (en) | 1984-10-03 | 1984-10-03 | Frazil ice concentration measuring apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1245721A true CA1245721A (en) | 1988-11-29 |
Family
ID=4128842
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000464700A Expired CA1245721A (en) | 1984-10-03 | 1984-10-03 | Frazil ice concentration measuring apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1245721A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013177695A1 (en) * | 2012-05-31 | 2013-12-05 | UNIVERSITé LAVAL | Method and apparatus for determining an icing condition status of an environment |
-
1984
- 1984-10-03 CA CA000464700A patent/CA1245721A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013177695A1 (en) * | 2012-05-31 | 2013-12-05 | UNIVERSITé LAVAL | Method and apparatus for determining an icing condition status of an environment |
| US9846261B2 (en) | 2012-05-31 | 2017-12-19 | UNIVERSITé LAVAL | Method and apparatus for determining an icing condition status of an environment |
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