Complex Impedance Moisture Sensor and Sensing Method

Abstract

An insulated pipe includes an elongated tube having a first end, a second end, and a sidewall extending therebetween, including an inner surface and an outer surface. The insulated pipe also includes an insulating member covering a portion of the outer surface of the sidewall and a planar moisture sensor. The planar moisture sensor is positioned in the insulating member or between the insulating member and the outer surface of the tube sidewall. The planar moisture sensor includes: a first electrode having a flat conductive member having an inner surface and an outer surface; a second electrode spaced apart from the first electrode having a flat conductive member having an inner surface and an outer surface, and a dielectric layer. The dielectric layer includes an absorbent dielectric polymer material positioned between and in electrical contact with the inner surfaces of the first electrode and the second electrode.

The invention claimed is: 
     
         1 . An insulated pipe comprising:
 a hollow, elongated member comprising an open first end, an open second end, and a sidewall extending therebetween, the sidewall comprising an inner surface and an outer surface;   at least one coaxial moisture sensor on the outer surface of the elongated member; and   insulation at least partially covering a portion of the outer surface of the sidewall of the elongated member and the at least one coaxial moisture sensor,   wherein the at least one coaxial moisture sensor comprises:
 a dielectric sleeve defining a center hole formed from an absorbent dielectric material, 
 an outer electrode electrically connected with an outer surface of the dielectric sleeve, and 
 an inner electrode comprising a wire extending through the center hole of and electrically connected with an inner surface of the dielectric member. 
   
     
     
         2 . The insulated pipe of  claim 1 , further comprising sensor electronics operatively connected to the first electrode and/or the second electrode of the at least one coaxial moisture sensor to measure an electrical property of the at least one coaxial moisture sensor to determine an amount of moisture absorbed by the dielectric sleeve, wherein the sensor electronics comprise:
 a power source for applying alternating electrical current to at least one of the inner electrode and the outer electrode; and   an electrical measurement device configured to measure a complex impedance (ohms) of the dielectric member.   
     
     
         3 . The insulated pipe of  claim 2 , wherein the sensor electronics further comprise a controller operatively connected to the power source and to the electrical measurement device, and wherein the controller is configured to cause the power source to periodically apply the alternating electrical current to at least one of the inner electrode or the outer electrode. 
     
     
         4 . The insulated pipe of  claim 3 , wherein the controller is further configured to determine an amount of moisture absorbed by the dielectric sleeve based on the measured complex impedance. 
     
     
         5 . The insulated pipe of  claim 1 , wherein the dielectric sleeve is in electrical contact with the inner electrode and the outer electrode, and maintains the inner electrode and the outer electrode spaced from one another. 
     
     
         6 . The insulated pipe of  claim 1 , wherein the at least one coaxial moisture sensor is wrapped around at least a portion of the outer surface of the elongated member forming a coil. 
     
     
         7 . The insulated pipe of  claim 1 , wherein the at least one coaxial moisture sensor extends axially along at least a portion of the outer surface of the elongated member along a line parallel to a curvilinear central longitudinal axis of the elongated member. 
     
     
         8 . The insulated pipe of  claim 1 , comprising multiple coaxial moisture sensors spaced about a circumference of the sidewall of the elongated member and extending axially along at least a portion of the outer surface of the elongated member along lines parallel to a curvilinear central longitudinal axis of the elongated member. 
     
     
         9 . The insulated pipe of  claim 1 , wherein the insulation comprises at least one of open cell foam insulation, closed cell foam insulation, fiber glass insulation, cellulose insulation, cotton batts, mineral wool, or wool batts. 
     
     
         10 . The insulated pipe of  claim 1 , wherein the dielectric material comprises a dielectric polymer. 
     
     
         11 . The insulated pipe of  claim 1 , wherein the dielectric material comprises at least one of nylon 4-6, nylon 6, nylon 6-6, nylon 6-12, nylon 11, polyamide-imide, polybenzimidazole, polyethersulfone, or polysulfone. 
     
     
         12 . The insulated pipe of  claim 1 , wherein the outer electrode comprises a moisture permeable sleeve, which permits moisture to pass to the dielectric sleeve. 
     
     
         13 . The insulated pipe of  claim 1 , wherein the first electrode or the second electrode comprise at least one of ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, gold, copper, tin, nickel, chromium, aluminum, or mixtures, alloys, or combinations thereof. 
     
     
         14 . The insulated pipe of  claim 1 , wherein a maximum outer diameter of the at least one coaxial sensor is less than 0.060 inch. 
     
     
         15 . A method of assembling an insulated pipe comprising:
 providing a hollow, elongated member comprising an open first end, an open second end, and a sidewall extending therebetween, the sidewall comprising an inner surface and an outer surface;   attaching at least one coaxial moisture sensor on an outer surface of the elongated member; and   attaching insulation to the outer surface of the elongated member, such that the insulation at least partially covers a portion of the outer surface of the sidewall of the elongated member and the at least one coaxial moisture sensor,   wherein the at least one coaxial moisture sensor comprises:
 a dielectric sleeve defining a center hole formed from an absorbent dielectric material, 
 an outer electrode electrically connected with an outer surface of the dielectric sleeve, and 
 an inner electrode comprising a wire extending through the center hole of and electrically connected with an inner surface of the dielectric member. 
   
     
     
         16 . The method of  claim 15 , further comprising operatively connecting the inner electrode and the outer electrode to sensor electronics to measure an electrical property of the at least one coaxial moisture sensor to determine an amount of moisture absorbed by the dielectric sleeve, wherein the sensor electronics comprise:
 a power source for applying alternating electrical current to at least one of the inner electrode and the outer electrode; and   an electrical measurement device configured to measure a complex impedance (ohms) of the dielectric member.   
     
     
         17 . The method of  claim 15 , wherein attaching the at least one coaxial moisture sensor on the outer surface of the elongated member comprises wrapping the at least one coaxial moisture sensor around at least a portion of the outer surface of the elongated member forming a coil. 
     
     
         18 . The method of  claim 15 , wherein attaching the at least one coaxial moisture sensor on the outer surface of the elongated member comprises attaching the at least one coaxial moisture sensor to the outer surface of the elongated member along a line parallel to a curvilinear central longitudinal axis of the elongated member. 
     
     
         19 . The method of  claim 15 , wherein attaching the at least one coaxial moisture sensor on the outer surface of the elongated member comprises attaching multiple coaxial moisture sensors to the elongated member, such that the multiple coaxial moisture sensors are spaced about a circumference of the sidewall of the elongated member and extend axially along at least a portion of the outer surface of the elongated member along lines parallel to a curvilinear central longitudinal axis of the elongated member. 
     
     
         20 . A method for detecting moisture in insulation surrounding a pipe, the method comprising:
 applying an alternating electrical current to at least one coaxial moisture sensor positioned between an outer surface of a hollow, elongated member and insulation covering at least a portion of the outer surface of the elongated member, the at least one coaxial moisture sensor comprising: a dielectric sleeve defining a center hole formed from an absorbent dielectric material, an outer electrode electrically connected with an outer surface of the dielectric sleeve, and an inner electrode comprising a wire extending through the center hole of and electrically connected with an inner surface of the dielectric member;   continually or periodically measuring a complex impedance of the absorbent dielectric material with sensor electronics connected to the inner and/or the outer electrode; and   determining an amount of moisture within the insulation based on the measured complex impedance.