Marine salinity measuring arrangement and method

Abstract

The invention relates to an arrangement for measuring salinity in water, which arrangement is part of an impressed current cathodic protection system having an electrical circuit comprising a source of electrical power (310); at least one first electrode (315) connected to a positive pole of the power source (310); at least one second electrode (317) connected to a negative pole of the power source (310); a voltage sensor (341); a current sensor (342); and a control unit (313). The control unit is arranged to initiate a measurement sequence at predetermined intervals, wherein the control unit is arranged to connect at least one first electrode (315) to the negative pole of the power source (310) to act as a cathode; connect at least one passive electrode (326) to the positive pole of the power source (310) to act as an active anode; register the output voltage; register the current; determine the circuit resistance using the output voltage and the current; and calculate the resistivity of the electrolyte based on the determined circuit resistance and at least one stored electrode property value, which resistivity is inversely proportional to the salinity. The invention further relates to a vessel provided with such a measuring arrangement and a method for its operation.

1 .- 15 . (canceled) 
     
     
         16 . Arrangement for measuring salinity in water, which arrangement comprises an impressed current cathodic protection system having an electrical circuit comprising:
 a source of electrical power from a direct current power source;   at least one first electrode connected to a positive pole of the power source whereby the at least one first electrode is an active anode;   at least one second electrode connected to a negative pole of the power source whereby the at least one second electrode is a cathode;   at least one sacrificial electrode normally disconnected from the circuit;   a voltage sensor detecting an output voltage impressed on the circuit;   a current sensor detecting a current supplied to the circuit; and   a control unit for controlling the impressed current cathodic protection system;   
       characterized in that the control unit is operable to initiate a measurement sequence at predetermined intervals, during which measurement sequence the control unit is operable to;
 connect at least one first electrode to the negative pole of the power source whereby the at least one first electrode is a cathode; 
 connect at least one sacrificial electrode to the positive pole of the power source whereby the at least one sacrificial electrode is an active anode; wherein the control unit is operable to register the output voltage and the current in order to determine the circuit resistance; and further operable to perform a calculation of the resistivity of the electrolyte based on the determined circuit resistance and at least one stored electrode property value, which resistivity is inversely proportional to the salinity. 
 
     
     
         17 . Arrangement according to  claim 16 , characterized in that the at least one stored electrode property value is the surface area of the sacrificial electrode. 
     
     
         18 . Arrangement according to  claim 17 , characterized in that the control unit is operable to calculate the resistivity using the formula: 
       
         
           
             
               
                 R 
                 c 
               
               = 
               
                 k 
                 * 
                 ρ 
                 * 
                 
                   ( 
                   
                     1 
                     
                       
                         A 
                         a 
                       
                     
                   
                   ) 
                 
               
             
           
         
       
       wherein: R c  is the circuit resistance;
 k is a correlation factor; 
 A a  is the surface area of the active electrode. 
 
     
     
         19 . Arrangement according to  claim 17 , characterized in that a further electrode property value is the surface area of the first electrode connected to the negative pole. 
     
     
         20 . Arrangement according to  claim 19 , characterized in that the control unit is operable to calculate the resistivity using the formula: 
       
         
           
             
               
                 R 
                 c 
               
               = 
               
                 k 
                 * 
                 ρ 
                 * 
                 
                   ( 
                   
                     
                       1 
                       
                         
                           A 
                           a 
                         
                       
                     
                     + 
                     
                       1 
                       
                         
                           A 
                           c 
                         
                       
                     
                   
                   ) 
                 
               
             
           
         
       
       wherein: R c  is the circuit resistance;
 k is a correlation factor; 
 A a  is the surface area of the sacrificial electrode; 
 A c  is the surface area of the electrode acting as a cathode. 
 
     
     
         21 . Arrangement according to  claim 16 , characterized in that the control unit is operable to maintain the impressed current cathodic protection system in operation if the determined resistivity is above a set threshold value. 
     
     
         22 . Arrangement according to  claim 16 , characterized in that the control unit is operable to determine a current salinity value based on the determined resistivity and to generate an output signal indicating the salinity value to a user. 
     
     
         23 . Arrangement according to  claim 16 , characterized in that the control unit is operable to monitor changes in the determined resistivity; to compare an increase in the determined resistivity to stored values for resistivity; and to determine if the increase is indicative of an electrical circuit malfunction. 
     
     
         24 . Arrangement according to  claim 16 , characterized in that the control unit is operable to disconnect each second electrode from the negative pole of the power source during the measuring sequence. 
     
     
         25 . Marine vessel characterized in that the marine vessel is provided with an impressed current cathodic protection system comprising an arrangement for measuring salinity according to  claim 16 . 
     
     
         26 . A method for measuring salinity in water using an impressed current cathodic protection system onboard a marine vessel; the impressed current cathodic protection system having an electrical circuit comprising:
 a source of electrical power from a direct current power source
 at least one first electrode connected to a positive pole of the power source to act as an active anode; 
   at least one second electrode connected to a negative pole of the power source to act as a cathode;   at least one sacrificial electrode normally disconnected from the circuit;   a voltage sensor detecting an output voltage impressed on the circuit;   a current sensor detecting a current supplied to the circuit; and   a control unit for controlling the impressed current cathodic protection system;   
       characterized by performing the following steps:
 initiating a measurement sequence at predetermined intervals; and 
 
       during the measurement sequence performing the further steps of:
 connecting the at least one first electrode to the negative pole of the power source; 
 connecting the at least one sacrificial electrode to the positive pole of the power source; 
 registering the output voltage; 
 registering current; 
 determining the circuit resistance using said output voltage and current, and 
 calculating the resistivity of the electrolyte based on the determined circuit resistance and at least one stored electrode property value, which resistivity is inversely proportional to the salinity. 
 
     
     
         27 . A method according to  claim 26 , characterized by calculating the resistivity of the electrolyte based on the determined circuit resistance and the surface area of the sacrificial electrode. 
     
     
         28 . A method according to  claim 27 , characterized by calculating the resistivity of the electrolyte based on the determined circuit resistance and the surface area of the first electrode connected to the negative pole. 
     
     
         29 . A method according to  claim 27 , characterized by calculating the resistivity of the electrolyte based on the determined circuit resistance and the combined surface area of each electrode connected to the negative pole. 
     
     
         30 . Method according to any one of  claim 26 , characterized by maintaining the impressed current cathodic protection system in operation if the determined resistivity is above a set threshold value.