Method and apparatus for measuring accumulated and instant rate of material loss or material gain

Abstract

Apparatus for measuring accumulated and instant rate of material loss or material gain of metal elements for the detection of metal deposition and corrosion includes a metal probe that is inserted into a measurement environment, causing the probe to experience metal deposition or corrosion. The probe has a corrosion-resistant first section and a corrodible second section. A temperature-compensated circuit receives an input signal from each of the first and second sections of the probe, whereby the circuit maintains a substantially constant voltage across the first section and generates a reference signal and a measurement signal. The circuit conditions and converts the reference signal and the measurement signal to produce first and second digitized output signals for inputting to a microprocessor.

1 . An apparatus for measuring a rate of corrosion of a corrosive medium, comprising: 
 a metal element exposed to the corrosive medium and having a corrosion-resistant first section and a corrodible second section;    a temperature-compensated circuit receiving an input signal from each of the first and second sections of the metal element, whereby the circuit maintains a substantially constant voltage across the first section, the circuit generating a reference signal and a measurement signal; and    means in the circuit for conditioning and converting the reference signal and the measurement signal to produce first and second digitized output signals for inputting to a microprocessor.    
   
   
       2 . The apparatus of  claim 1 , wherein the first section of the metal element comprises a coated section, and wherein the second section of the metal element comprises a non-coated section.  
   
   
       3 . The apparatus of  claim 1 , wherein the metal element further comprises an interface providing electrical and thermal connection between the first and second sections.  
   
   
       4 . The apparatus of  claim 3 , wherein the circuit comprises: 
 a first current generator that directs a first current to the interface, and to the first and second sections through first balancing means, thereby generating the first and second input signals respectively representing a first voltage across the first section and a second voltage across the second section;    a first voltage sensor, connected between the first and second sections, that generates the measurement signal representing the difference between the first and second voltages in response to the first and second input signals, respectively;    a second current generator that directs a second current to the interface, and to the first and second sections through second balancing means, thereby generating the first and second input signals respectively representing the first voltage across the first section and the second voltage across the second section; and    a second voltage sensor, connected between the first section and the interface, that generates the reference signal representing the first voltage in response to the first input signal.    
   
   
       5 . The apparatus of  claim 4 , further comprising temperature compensation means that receives the reference signal from the second voltage sensor, and that generates first and second temperature-compensating feedback signals to the first and second current generators, respectively.  
   
   
       6 . The apparatus of  claim 5 , wherein the first and second feedback signals are proportional to the reference signal.  
   
   
       7 . The apparatus of  claim 1 , wherein the first and second sections of the metal element respectively have first and second resistances, and wherein the circuit comprises: 
 first and second resistors respectively connected to the first and second sections of the metal element, the first and second resistors having a third resistance that is substantially larger than the first and second resistances; and    a power transmitter amplifier that provides first and second excitation current signals that are respectively fed to the first and second sections of the metal element via the first and second resistors, respectively;    whereby a first voltage representing the reference signal is generated across the first section, and a second voltage representing the measurement signal is generated across the second section.    
   
   
       8 . The apparatus according to  claim 7 , wherein said first and second resistances of said metal element are in a range from about 4 μΩ to about 4 KΩ.  
   
   
       9 . The apparatus of  claim 7 , wherein the circuit further comprises: 
 a differential sensor amplifier connected across both the first and second sections of the metal element so as to generate a DC output signal representing the difference between the first and second voltages.    
   
   
       10 . The apparatus of  claim 9 , wherein the power transmitter amplifier is a first power transmitter amplifier that generates the first and second excitation current signals having a first frequency in response to a first analog voltage input signal, wherein the DC output signal is a first DC output signal, and wherein the circuit further comprises: 
 third and fourth resistors respectively connected to the first and second sections of the metal element, the third and fourth resistors having a fourth resistance that is of the same order of magnitude as the third resistance;    a second power transmitter amplifier that generates third and fourth excitation current signals having a second frequency in response to a second analog voltage input signal, and that are respectively fed to the first and second sections of the metal element via the third and fourth resistors, respectively; and    input signal generating means for generating the first and second analog voltage input signals, wherein the amplitudes of the first and second analog voltage input signals are substantially equal and are controlled on the basis of a feedback signal generated in response to a second DC output signal representing a voltage across the first section of the metal element.    
   
   
       11 . The apparatus of  claim 10 , wherein the input signal generating means comprises first and second potentiometers, the resistances of which are adjusted in response to the feedback signal to maintain a substantially constant voltage across the first and second sections of the metal element.  
   
   
       12 . The apparatus according to  claim 3 , wherein the metal element defines a predetermined cross sectional shape, wherein the metal element comprises a metallic composition, and wherein the interface comprises a structure selected from the group consisting of at least one of an electrically and thermally conductive wire, a direct contact between the first and second sections, and a boundary between the first and second sections that includes a metal piece.  
   
   
       13 . The apparatus of  claim 10 , wherein the first analog voltage input signal has a first frequency in the range of about 1 Hz to about 100 KHz; wherein the second analog voltage input signal has a second frequency in the range of about 1 Hz to about 100 KHz; wherein the first power transmitter amplifier provides the first excitation current signal comprising a square-wave signal having the first frequency; wherein the second power transmitter amplifier provides the second excitation current signal comprising a square-wave signal having the second frequency; and wherein the apparatus further comprises: 
 a first sensor amplifier that provides a selective amplification of part of the first DC output signal constituted by the first frequency; and    a second sensor amplifier that provides a selective amplification of part of the second DC output signal constituted by the second frequency.    
   
   
       14 . The apparatus of  claim 10 , wherein the first and second DC output signals have voltages in the range of about −24V to about +24V.