Methods and apparatus for measuring electrical conductivity

Apparatus for use in indicating the electrical conductivity of a liquid in an electrical conductivity cell having a pair of terminals wherein said liquid is disposed in series between said terminals, said apparatus comprising:

• an oscillator having a resistance-capacitance network which includes said cell;
• a capacitor connected in series with said oscillator;
• an electronic device having sensing leads connected in series with said capacitor, said electronic device having different conductance conditions in response to application of high potential and low potential, respectively, across said sensing leads;
• a reference conductance;
• a source of electrical potential;
• means for applying potential from said source to said resistance-capacitance network to charge said capacitor through said cell until the increase in potential resulting from such charge causes said electronic device to change its conductance condition to permit the capacitor to discharge through said cell and reduce the potential applied to said capacitor, thereby causing the electronic device to again change its conductance condition, thereby completing an operating cycle;
• whereby the time period of said operating cycle is proportional to the conductivity of said liquid.

In a method of measuring the electrical conductivity of liquid in a conductivity cell, the steps of:

• (a) passing current in a first direction through said conductivity cell and through a capacitor connected in series with said conductivity cell until a first predetermined voltage appears across said capacitor;
• (b) in response to said first predetermined voltage appearing across said capacitor, passing current in a second direction, opposite said first direction, through said conductivity cell and said capacitor until the voltage across the capacitor reaches a second predetermined level;
• (c) in response to the voltage across said capacitor reaching said second predetermined level, repeating steps (a) and (b) cyclically;
• whereby the times required for the voltage across the capacitor to reach said first and second predetermined levels depends upon the conductance of said conductivity cell.