Apparatus for measuring ph with temperature compensating diode means

Claim 1

IN A PH MEASURING AND CONTROLLING APPARATUS HAVING A GLASS MEASURING ELECTRODE, A REFERENCE ELECTRODE, AMPLIFYING MEANS ARRANGED TO AMPLIFY A DIFFERENCE IN POTENTIAL BETWEEN SAID MEASURING ELECTRODE AND SAID REFERENCE ELECTRODE, AS A REPRESENTATION OF THE PH OF A TEST FLUID AND PH CONTROL APPARATUS RESPONSIVE TO AN OUTPUT SIGNAL FROM SAID AMPLIFYING MEANS AND ARRANGED TO CONTROL THE PH OF SAID TEST FLUID AT A DESIRED PH, THE IMPROVEMENT COMPRISING A RECTIFYING SEMICONDUCTOR MEANS HAVING A FORWARD VOLTAGE DROP HAVING A TEMPERATURE DEPENDENCE WHICH IS SUBSTANTIALLY THE SAME AS THAT OF THE MEASURING ELECTRODE, THERMALLY CONDUCTIVE, ELECTRICALLY INSULATING MEANS ENCLOSING SAID RECTIFYING MEANS AND ADAPTED TO THERMALLY EXPOSE SAID RECTIFYING MEANS TO SAID TEST FLUID WHILE ELECTRICALLY ISOLATING SAID RECTIFYING MEANS FROM SAID TEST FLUID, AND CIRCUIT MEANS CONNECTING SAID RECTIFYING MEANS IN SERIES WITH SAID MEASURING ELECTRODE SUCH THAT THE VOLTAGE DROP ACROSS THE SAID RECTIFYING MEANS IS SUBTRACTED FROM THE POTENTIAL BETWEEN THE SAID ELECTRODES.