BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of the sensing component of the invention adapted to sense the capacitance of the ice slurry;
FIG. 2 is a diagram of the invention as shown in FIG. 1 including a temperature sensor;
FIG. 3 is a diagram of an alternative sensing component of the invention adapted to sense the capacitance of the ice slurry;
FIG. 4 is a diagram of an RC oscillator circuit;
FIG. 5 is a diagram of a sensing circuit to measure the ice fraction of an ice slurry;
FIG. 6 is a diagram of the sensing component of the invention adapted to sense the impedance of the ice slurry; and
FIG. 7 is a diagram of an alternative sensing circuit to measure the ice fraction of an ice slurry.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 an embodiment of the electrical property sensing part 100 of an ice fraction sensor is shown, connectable in line in ice slurry flow to, in use, sense the ice fraction of the slurry passing therethrough by capacitive means. The sensing part comprises body section 102 made of a plastics molding, preferably one with good low temperature characteristics, for example polypropylene. Encapsulated within the body section 102 are electrode plates 104106, made of electrically conductive materials, in spaced relationship to one another and arranged such that in use the ice slurry passing through the sensing part 100 passes between plates 104 and 106. The plates 104106 are encapsulated wholly within the body 102 such that the body forms a barrier between the plates 104106 and the slurry passing therebetween. The body 102 is of an electrically insulating material so as to prevent conduction from one plate to the other via the ice slurry. Electrode plates 104106 are connected to a sensing circuit by connectors 108110.
Referring to FIG. 2 the electrical property sensing part of FIG. 1 is shown which in addition has a temperature sensor 202 for detecting the temperature of the ice slurry passing through the sensor. The temperature sensor is connected to the sensing circuit by means of electrical connection 204 to carry a signal, indicative of the temperature of the ice slurry passing therethrough, to the sensing circuit. The sensor may be directly in contact with the fluid as shown in the Figure or may be isolated therefrom by the body section 206 in the same manner as are the plates 208210 to protect the temperature sensor from the ice slurry.
Referring to FIG. 3 the electrical property sensing part an alternative arrangement of the sensing part shown in FIG. 1 also adapted, in use, to sense the ice fraction of the slurry passing therethrough by capacitive means, is shown. The sensing part 300 comprises an electrically conductive joining element 302 having a central bore therethrough for joining two sections of tube 304, 306 such that an ice slurry can pass from one tube to the other via the central bore 308 of the joining element such that said ice slurry passing through the central bore 308 comes into electrical contact therewith. Surrounding both of the tubes 304, 306, sufficiently spaced from the ends thereof such that when assembled onto the joining element 302 there is no overlap therewith, is an electrically conductive collar 310, 312. The collars 310 are insulated from electrical contact with the ice slurry by means of the tube 304, 306 walls and are together connected to an electrical sensing circuit by connector 314. The joining element 302 is connected to the same sensor circuit by connector 316 such that the joining element 302 and the two collars 310, 312 form electrodes of a capacitor. The sensing part 300 may also include a temperature sensor as described in relation to FIG. 2 for sensing the temperature of the ice slurry passing therethrough.
In use, the sensing part as described in reference to FIGS. 1 to 3 is used as the capacitor 404 of an RC oscillator circuit shown in FIG. 4 comprising an oscillator chip 402 (which could be for example a CD74HC132 chip from “Texas Instruments”), a capacitor 404 and a resistor 406. Referring to FIG. 5, the changing capacity of the sensing part 100, 200, 300 as the ice fraction of the slurry passing therethrough varies, results in a change in the output frequency of the RC oscillator circuit 502 (as shown in FIG. 4). The output 504 of the oscillator circuit 502 is inputted into a controller 506 which outputs a varying electrical signal 508 of 4-20 mA, the magnitude of output signal directly indicative of the ice fraction. The controller 506 includes a processor 510 and a first look up table 512 which contains data correlating the frequency of the oscillator to the ice fraction of the slurry. Where a temperature sensor is included in the sensing part 100, 200, 300, the controller 506 monitors the temperature and detects the temperature at which ice formation begins. This temperature can then be used in association with a second look up table 514 to detect an offset, related to the to concentration of a freezing point suppressant in the ice slurry, the offset being used to offset either the frequency of the oscillator prior to inputting it to the lookup table, or alternatively to offset the output from the lookup table, or a processed signal dependant thereon to compensate the outputted ice fraction for varying concentrations freezing point suppressant within the ice slurry.
Referring to FIG. 6 an embodiment of the sensing part 600 of an ice fraction sensor is shown, connectable in line in ice slurry flow to sense the ice fraction of the slurry passing therethrough by inductive means. The sensing part comprising a body section 602 made of a plastics moulding, preferably one with good low temperature characteristics, for example polypropylene. Encapsulated within the body section 602 are two electrically conductive plates 604, 606 forming electrodes in spaced relationship to one another and arranged such that they are in electrical contact with the ice slurry passing therebetween thereby using the impedance of the sensing part to influence an electrical circuit as shown in FIG. 5 by means of electrical connection 608, 610 therewith. The sensing part of this arrangement is used to replace the resistor 406 of the RC oscillator of FIG. 4. The oscillating output signal from the RC oscillator is processed by a controller, in the same way as described in reference to FIG. 5, to generate an output signal indicative of the ice fraction.
Referring to FIG. 7 sensing part 701 of an ice fraction sensor has a pair of electrodes and a temperature sensor. A sinusoidal wave generator 703 supplies an oscillating signal to the sensing part 701 and a impedance analyzer 702 (for example part number AD8302 from Analogue Devices) creates output signals 704 relating to the amplitude and phase of the impedance of the circuit containing the electrodes. A signal processing means 705 includes a microcontroller 706 which receives the signals 704 and performs an algorithm on them to calculate either the conductivity or the reactance of the circuit as described hereinbefore. The microcontroller also receives a signal 709 relating to the temperature of the fluid passing through the sensing part 701.
When the fluid is in its fully liquid state the wave generator 703 creates a low frequency signal of around 1 MHz and the microcontroller calculates the conductivity R of the circuit. The microcontroller 706 then compares the temperature and the conductivity to a look-up table 707 to calculate an offset relating to the percentage antifreeze in the fluid being measured. When the fluid is part ice and part liquid the wave generator 703 creates a high frequency signal in excess of 25 MHz and the microcontroller 706 calculates the conductivity R of the circuit. The microcontroller 706 then compares the conductivity to a look up table 708 and offsets the correlated ice fraction by the offset calculated when the fluid was in its fully liquid phase to calculate a measured ice fraction of the ice liquid mixture and outputs a signal 710 indicative of the ice fraction.
Patent Application
20080088321
