Determine dissolved oxygen

The dissolved oxygen concentration is usually in mg/L (dissolved oxygen per liter of water) or ppm (parts per million). Some meters compare the calculated oxygen content to the observed concentration to give a percentage of saturation (O2% sat.)

There are two ways to determine dissolved oxygen, polarographic and galvanic. Polarographic electrodes require instrument input and voltage to electrode polarization. 

Since the applied voltage may take 15 minutes to stabilize, the polarographic electrode is usually preheated before use to ensure proper polarization of the electrode. The two poles of the galvanic cell type are composed of two different metals capable of generating a voltage by spontaneous polarization. Since the galvanic cell voltage is generated spontaneously rather than externally, the galvanic cell electrode does not require the "preheating" required for polarographic electrode polarization.