Sensor for measuring the electrical conductivity of a fluid medium

Abstract

The invention relates to an inductively operating sensor ( 1 ) for measuring the electrical conductivity of a fluid medium ( 2 ), having an excitation coil ( 3 ), to which an input signal is fed, and a receiver coil ( 4 ) coupled with the former via the fluid medium ( 2 ), which provides an output signal (I Ind ), which is a measurement for the conductivity of the fluid medium ( 2 ). To make possible the timely detection of damage to the windings of the excitation coil ( 3 ) or the receiver coil ( 4 ), or respectively a service cable for the sensor ( 1 ), which leads to leak currents or short circuits, it is proposed by the invention that the sensor ( 1 ) has means ( 5 ) for measuring a variable signal at the input of the excitation coil ( 3 ). The excitation coil ( 3 ) of the sensor is preferably fed by an input voltage (U Err ), and the means ( 5 ) for measuring the variable signal preferably measure the input current (I Err ) at the input of the excitation coil ( 3 ).

What is claimed is:  
     
         1 . An inductively operating sensor ( 1 ) for measuring the electrical conductivity of a fluid medium ( 2 ), having an excitation coil ( 3 ), to which an input signal is fed, and a receiver coil ( 4 ) coupled with the former via the fluid medium ( 2 ), which provides an output signal (I Ind ), which is a measurement for the conductivity of the fluid medium ( 2 ), characterized in that the sensor ( 1 ) has means ( 5 ) for measuring a variable signal at the input of the excitation coil ( 3 ).  
     
     
         2 . The sensor ( 1 ) in accordance with  claim 1 , characterized in that the sensor ( 1 ) has a voltage source, which feeds an input voltage (U Err ) to the excitation coil ( 3 ), and that the means ( 5 ) for measuring the variable signal pick up the input current (I Err ) at the input of the excitation coil ( 3 ).  
     
     
         3 . The sensor ( 1 ) in accordance with  claim 2 , characterized in that the means ( 5 ) for measuring the input current (I Err ) have a multiplier (R) and measure the voltage (U) dropping across the multiplier (R).  
     
     
         4 . The sensor ( 1 ) in accordance with one of  claims 1  to  3 , characterized in that the sensor ( 1 ) has a measured value transducer for receiving the output signal (I Ind ), which is connected with the means ( 5 ) for measuring the variable signal at the input of the excitation coil ( 3 ), that the means ( 5 ) generate a status signal, which is a function of the measured value of the variable signal at the input of the excitation coil ( 3 ), and that the means ( 5 ) feed the status signal to the measured value transducer.  
     
     
         5 . The sensor ( 1 ) in accordance with  claim 4 , characterized in that the measured value transducer corrects the output signal (I Ind ) as a function of the strength of the status signal.  
     
     
         6 . The sensor ( 1 ) in accordance with  claim 4  or  5 , characterized in that the measured value transducer causes a signal to be issued, if the status signal lies outside of a defined threshold range.