Sensor and sensor system for liquid conductivity, temperature and depth

Abstract

Liquid conductivity and temperature are measured in respective sensitivity fields that are collocated—i. e., in volumes that nearly match by mathematical, geometrical, or functional criteria. Collocation is as distinct from mere adjacency or proximity; and is with respect to measurement volumes, not measuring hardware. Preferably pressure too is measured with sensitivity very generally collocated to the conductivity and temperature sensitivity. Preferably, respective temporal/spatial bandwidths of the two (or three) sensors are matched. Preferably the pressure sensor is a MEMS transducer, the conductivity sensor is a four-terminal device, the thermometer is a thermistor encapsulated in a silkscreened glass wall, and circuits (1) compensate for time lag between conductivity and temperature measurement, (2) remove artifacts due to detritus in or near either sensor, and (3) derive secondary parameters of the liquid.

What is claimed is:  
     
         1 . Apparatus for determining parameters of a liquid; said apparatus comprising: 
 a conductivity sensor for measuring electrical conductivity of such liquid; and    a thermometer for measuring temperature of such liquid;    wherein a sensitivity field of the conductivity sensor and a sensitivity field of the thermometer are substantially collocated.    
     
     
         2 . The apparatus of  claim 1 , wherein substantial collocation is defined as satisfying at least one of these criteria: 
 a crosscorrelation coefficient for the two fields, calculated geometrically without regard to characteristics of such liquid, and assuming no mixing of such liquid and no spatial lag, is between 0.01 and unity,    a ratio of (a) crosscorrelation coefficient for the two fields in their actual relative locations to (b) crosscorrelation coefficient for said two fields in ideal relative locations but without change of relative size, both coefficients being calculated geometrically without regard to characteristics of such liquid, and assuming no mixing of such liquid and no spatial lag, is between 0.9 and unity,    one sensor is positioned between plural primary lobes of the other's sensitivity function,    one of the sensors is positioned within a most direct path of sensitivity field lines of the other sensor,    the two fields effectively monitor substantially identical volumes of such liquid,    the two fields effectively monitor volumes of such liquid that are nested, and    the two sensors both monitor volumes of such liquid sampled from a common mixing volume.    
     
     
         3 . The apparatus of  claim 1 , further comprising: 
 a pressure sensor for measuring pressure in a pressure-measurement volume of such liquid;    wherein a sensitivity field of the pressure sensor is very generally collocated with the conductivity- and temperature-measurement sensitivity fields.    
     
     
         4 . The apparatus of  claim 3 , wherein: 
 the conductivity sensor has a temporal response bandwidth and a spatial response bandwidth;    the thermometer has a temporal response bandwidth and a spatial response bandwidth;    the temporal bandwidths of the conductivity sensor and thermometer are effectively matched to each other; and    the spatial bandwidths of the conductivity sensor and thermometer are effectively matched to each other.    
     
     
         5 . The apparatus of  claim 1 , wherein: 
 the conductivity sensor has a temporal response bandwidth and a spatial response bandwidth;    the thermometer has a temporal response bandwidth and a spatial response bandwidth;    the temporal bandwidths of the conductivity sensor and thermometer are effectively matched to each other; and    the spatial bandwidths of the conductivity sensor and thermometer are effectively matched to each other.    
     
     
         6 . The apparatus of  claim 5 , further comprising: 
 a pressure sensor for measuring pressure in a pressure-measurement volume of such liquid;    wherein a sensitivity field of the pressure sensor is very generally collocated with the conductivity- and temperature-measurement sensitivity fields.    
     
     
         7 . The apparatus of  claim 1 , further comprising: 
 a pressure sensor mounted in a common unitary assembly with the conductivity and temperature sensors.    
     
     
         8 . The apparatus of  claim 10 , wherein: 
 the pressure sensor is a MEMS transducer.    
     
     
         9 . The apparatus of  claim 1 , wherein: 
 the conductivity sensor is a four-terminal device.    
     
     
         10 . The apparatus of  claim 9 , wherein: 
 the thermometer is a thermistor encapsulated within a silkscreened glass wall.    
     
     
         11 . The apparatus of  claim 1 , wherein:: 
 the thermometer is a thermistor encapsulated within a silkscreened glass wall.    
     
     
         12 . The apparatus of  claim 1 , further comprising: 
 a data-acquisition and -processing system connected to receive measurement signals from the conductivity sensor and thermometer, representing collocated values of conductivity and temperature;    the data-acquisition and -processing system comprising a circuit for correcting at least one of the measurement signals to compensate for time lag between measurements of conductivity and temperature.    
     
     
         13 . The apparatus of  claim 1 , further comprising: 
 a data-acquisition and -processing system connected to receive measurement signals from the conductivity sensor and thermometer, representing collocated values of conductivity and temperature;    the data-acquisition and -processing system comprising a circuit for modifying at least one of the measurement signals to remove signal artifacts due to detritus passing by or through the conductivity sensor or the thermometer.    
     
     
         14 . The apparatus of  claim 1 , further comprising: 
 a data-acquisition and -processing system fabricated in a substantially unitary assembly with the sensors, and connected to receive measurement signals from the sensors representing collocated values of conductivity and temperature;    the data-acquisition and -processing system comprising circuits for deriving from said measurement signals secondary parameters of such liquid for said substantially identical measurement volumes.    
     
     
         15 . The apparatus of  claim 14 , wherein: 
 the secondary parameters comprise density of such liquid and speed of sound in such liquid.    
     
     
         16 . The apparatus of  claim 14 , further comprising: 
 a pressure sensor for determining pressure of such liquid; and wherein:    the data-acquisition and -processing system further receives pressure-measurement signals from the pressure sensor representing values of pressure that are associated with values of conductivity and temperature measured by the conductivity sensor and thermometer; and    the data-acquisition and -processing system further derives, from said pressure-measurement signals, depth of such liquid.    
     
     
         17 . Apparatus for determining parameters of liquid; said apparatus comprising: 
 a conductivity sensor for measuring electrical conductivity of such liquid, said sensor having a temporal response bandwidth and a spatial response bandwidth; and    a thermometer for measuring temperature of such liquid, said thermometer having a temporal response bandwidth and a spatial response bandwidth; and wherein:    the temporal response bandwidths of the conductivity sensor and thermometer are effectively matched; and    the spatial response bandwidths of the conductivity sensor and thermometer are effectively matched.    
     
     
         18 . The apparatus of  claim 17 , further comprising: 
 a pressure sensor for measuring pressure, said pressure sensor having a temporal response bandwidth and a spatial response bandwidth; and wherein:    the temporal bandwidth of the pressure sensor is effectively matched to the temporal bandwidths of the conductivity sensor and thermometer; and    the spatial bandwidth of the pressure sensor is effectively matched to the spatial bandwidths of the conductivity sensor and thermometer.    
     
     
         19 . Apparatus for determining parameters of a liquid; said apparatus comprising: 
 a conductivity sensor for measuring electrical conductivity of such liquid;    a thermometer for measuring temperature of such liquid; and    a data-acquisition and -processing system connected to receive measurement signals from the conductivity sensor and thermometer;    the data-acquisition and -processing system comprising a circuit for correcting at least one of the measurement signals to compensate for time lag between measurements of conductivity and temperature.    
     
     
         20 . The apparatus of  claim 19 , wherein: 
 the data-acquisition and -processing system is fabricated in a substantially unitary assembly with the sensors and comprises circuits for deriving from said measurement signals secondary parameters of such liquid for said substantially identical measurement volumes.    
     
     
         21 . Apparatus for determining parameters of a liquid; said apparatus comprising: 
 a conductivity sensor for measuring electrical conductivity of such liquid;    a thermometer for measuring temperature of such liquid; and    a data-acquisition and -processing system connected to receive measurement signals from the conductivity sensor and thermometer, representing conductivity and temperature;    the data-acquisition and -processing system comprising a circuit for modifying at least one of the measurement signals to remove signal artifacts due to detritus passing by or through the conductivity sensor or the thermometer.    
     
     
         22 . The apparatus of  claim 21 , wherein: 
 the data-acquisition and -processing system is fabricated in a substantially unitary assembly with the sensors and comprises circuits for deriving from said measurement signals secondary parameters of such liquid.    
     
     
         23 . The apparatus of  claim 22 , wherein: 
 the secondary parameters comprise density of such liquid and speed of sound in such liquid.    
     
     
         24 . The apparatus of  claim 22 , further comprising: 
 a pressure sensor for determining pressure of such liquid; and wherein:    the data-acquisition and -processing system further receives pressure-measurement signals from the pressure sensor representing values of pressure that are associated with values of conductivity and temperature measured by the conductivity sensor and thermometer; and    the data-acquisition and -processing system further derives, from said pressure-measurement signals, depth of such liquid.    
     
     
         25 . The apparatus of  claim 24 , wherein: 
 the pressure sensor is a MEMS transducer.    
     
     
         26 . The apparatus of  claim 25 , wherein: 
 the transducer is embedded in a common chip that provides the data-acquisition and -processing system.    
     
     
         27 . The apparatus of  claim 21 , for use with said liquid being ocean, estuarine, or brackish water; and further comprising: 
 hardware for mooring the sensors in, or a vehicle and associated hardware for vehicle-mounting them in or towing them through such ocean, estuarine or brackish water.    
     
     
         28 . The apparatus of  claim 21 , wherein: 
 the circuit substitutes a signal representative of at least one period before or after the passing of the detritus, or both, in place of signal generated in response to the detritus.    
     
     
         29 . Apparatus for determining parameters of a liquid; said apparatus comprising: 
 two conductivity sensors for measuring electrical conductivity of such liquid; and    at least one thermometer for measuring temperature of such liquid; and    a structural assembly for supporting the sensor and thermometer, said assembly comprising at least two circuit cards or ceramic cards having structural strength to provide mechanical integrity to the assembly and mutually disposed in a parallel, substantially aligned relationship and having the two conductivity sensors at mutually opposed faces of two of said cards.    
     
     
         30 . The apparatus of  claim 29 , further comprising: 
 third and fourth circuit cards or ceramic cards also having structural strength to provide mechanical integrity to the assembly and disposed at substantially right angles, to, and for structural interconnection between, the first-mentioned two cards;    the four cards forming a substantially rectangular or square frame open at two ends for circulation of such liquid therethrough.    
     
     
         31 . The apparatus of  claim 30 , wherein: 
 the at least one thermometer comprises a resistance wire mounted across the frame.    
     
     
         32 . The apparatus of  claim 31 , wherein: 
 the resistance wire is connected at its two ends to points on the frame respectively associated with the two conductivity sensors.    
     
     
         33 . The apparatus of  claim 29 , wherein: 
 the at least one thermometer comprises a resistance wire mounted across the frame.    
     
     
         34 . The apparatus of  claim 33 , wherein: 
 the resistance wire is connected at its two ends to points on the frame respectively associated with the two conductivity sensors.    
     
     
         35 . The apparatus of  claim 34 , wherein: 
 the resistance wire is connected at its two ends to centerpoints of the two conductivity sensors respectively.    
     
     
         36 . The apparatus of  claim 30 , wherein: 
 at least one of the two conductivity sensors has concentric electrodes; and    the at least one thermometer comprises a thermistor mounted at a centerpoint of the concentric electrodes.    
     
     
         37 . The apparatus of  claim 29 , further comprising: 
 pillar-type standoffs also having structural strength to provide mechanical integrity to the assembly and disposed at substantially right angles to, and for structural interconnection between, the two cards;    the two cards and the pillar-type standoffs forming a substantially rectangular or square frame, generally open at four faces for circulation of such liquid therethrough.    
     
     
         38 . The apparatus of  claim 37 , wherein: 
 the at least one thermometer comprises a resistance wire mounted across the frame.    
     
     
         39 . The apparatus of  claim 38 , wherein: 
 the resistance wire is connected at its two ends to points on the frame respectively associated with the two conductivity sensors.    
     
     
         40 . The apparatus of  claim 38 , wherein: 
 the resistance wire is connected at its two ends to centerpoints of the two conductivity sensors respectively.    
     
     
         41 . The apparatus of  claim 37 , wherein: 
 at least one of the two conductivity sensors has concentric electrodes; and    the at least one thermometer comprises a thermistor mounted at a centerpoint of the concentric electrodes.    
     
     
         42 . The apparatus of  claim 29 , wherein: 
 the maximum dimension of each conductivity electrode is 1.5 centimeter.    
     
     
         43 . Apparatus for determining parameters of a liquid; said apparatus comprising: 
 at least one conductivity sensor for measuring electrical conductivity of such liquid; and    at least one thermometer for measuring temperature of such liquid;    circuitry connected to receive and manipulate electrical signals from the sensor and thermometer; and    a common ceramic substrate holding the sensor, thermometer and circuitry.    
     
     
         44 . The apparatus of  claim 43 , wherein: 
 the thermometer is a thermistor chip applied directly to a substrate holding the circuitry.    
     
     
         45 . The apparatus of  claim 43 , wherein: 
 the thermometer is a thermistor bead mounted in a niche in the circuitry.    
     
     
         46 . The apparatus of  claim 43 , wherein the circuitry comprises: 
 an analog-to-digital converter digitizing the signals;    memory means holding calibration coefficients for each sensor and each thermometer;    a data bus transmitting the signals with embedded calibration coefficients to a processing unit.    
     
     
         47 . The apparatus of  claim 46 , wherein: 
 the processing unit is programmed for plotting and data archiving.    
     
     
         48 . The apparatus of  claim 46 , wherein: 
 the processing unit is disposed, remote from the sensor and thermometer, in a vehicle or shore facility.    
     
     
         49 . The apparatus of  claim 43:   wherein the thermometer is a thermistor, having an asymptotic time-response function; and    the circuitry comprises a module that executes a program for calculating a limit value from early response data.    
     
     
         50 . Apparatus for determining parameters of a liquid; said apparatus comprising: 
 a tube for passage of such liquid therethrough;    at least one slot formed through a side wall of the tube;    a generally planar substrate mounted in the slot and extending inward from the slot across the tube interior, and also extending outward from the slot and projecting from the tube;    a conductivity sensor, formed on opposite sides of the portion of the substrate that extends across the tube interior, for measuring electrical conductivity of such liquid;    a thermometer for measuring temperature of such liquid.    
     
     
         51 . The apparatus of  claim 50 , wherein: 
 the conductivity sensor comprises electrodes extending along the substrate and across the tube, on said opposite sides of the substrate.    
     
     
         52 . The apparatus of  claim 51 , wherein: 
 the electrodes comprise, on each side of the substrate, two generally parallel current-driving electrodes, and a sensing electrode generally parallel to and between the driving electrodes.    
     
     
         53 . The apparatus of  claim 52 , wherein: 
 conductivity measurement paths extend through such liquid within and generally parallel to the tube, between the electrodes on one side of the substrate and the electrodes on the opposite side of the substrate, by passing around at least one edge of the substrate.    
     
     
         54 . The apparatus of  claim 53 , wherein: 
 the paths comprise two paths passing around two opposite edges of the substrate; and    said two paths define two conductivity-measurement sensitivity lobes extending in opposite generally axial directions within the tube from the sensing electrode on one side of the substrate to the sensing electrode that is on the side opposite said one side.    
     
     
         55 . The apparatus of  claim 54 , wherein: 
 the thermometer is mounted substantially between the two conductivity-measurement sensitivity lobes.    
     
     
         56 . The apparatus of  claim 54 , wherein: 
 the thermometer comprises two temperature sensors, one on each side of the substrate, each temperature sensor disposed substantially between the two conductivity-measurement sensitivity lobes.    
     
     
         57 . The apparatus of  claim 50 , wherein: 
 the electrodes are silkscreened on the substrate.    
     
     
         58 . The apparatus of  claim 50 , wherein: 
 the tube is of alumina.    
     
     
         59 . Apparatus for determining parameters of a liquid; said apparatus comprising: 
 a conductivity sensor for measuring electrical conductivity of such liquid, the sensor having concentric annular electrodes; and    a thermometer for measuring temperature of such liquid, the thermometer being disposed within an innermost of the annular electrodes.    
     
     
         60 . A process for manufacturing apparatus for measuring liquid conductivity; said process comprising the steps of: 
 manufacturing a conductivity sensor that provides good measurement characteristics for any one of multiple different measurement applications;    providing a circuit substrate that is compatible with the sensor and with any of the multiple different measurement applications;    selecting a circuit configuration, for use with the sensor, from multiple different circuit configurations associated with the multiple measurement applications respectively;    causing the selected circuit configuration to be formed on the substrate and interconnected with the sensor; and    encapsulating the circuit and substrate.