How Do Dissolved Oxygen Probes Work?
Dissolved oxygen probes deal with redox (redox) reactions, providing continuous and real-time measurements. Because they have an applied voltage, most DO probes require a "warm-up time" before use to polarize the electrodes before measuring DO in water.
After connecting the dissolved oxygen probe to the meter, immerse the electrode sensor (dissolved oxygen probe) into the solution to be measured. When the DO sensor is connected to the meter, voltage can be applied to the internal electrodes. Oxygen (O2) molecules reach the membrane and diffuse through the permeable/semi-permeable membrane to the electrodes. A small electric current flows between the electrodes (cathode and anode). The amount of current flowing between the electrodes is proportional to the O2 concentration in the solution. The amount of dissolved oxygen in solution is measured by measuring the current using a calibrated meter.
However, dissolved oxygen sensors do have disadvantages when performing DO measurements. The amount of O2 it consumes from solution is equal to the amount diffused in the sensor. As a result, the amount of O2 in the vicinity of the DO probe is reduced, so if a current probe is used, the DO probe must be stirred in the solution to obtain an accurate measurement.
Electrodissolved oxygen sensor probe
The original electrokinetic DO probe generates a voltage when O2 diffuses through the probe membrane. A thin, semipermeable membrane allows oxygen to pass through and blocks everything else.
As the O2 passes through the membrane and electrolyte to the electrode, it dissolves inside the probe cap containing the buffered electrolyte, allowing the O2 to react with the cathode (platinum electrode) to gain electrons. It is this electron that is donated to the O2 molecule to create a voltage between the anode (silver chloride electrode) and cathode within the DO probe.
Once the DO probe detects the current, the connected meter can convert the reading to DO concentration.
Polarographic dissolved oxygen sensor probe
Polarized DO probes also contain a thin semipermeable membrane, however, a voltage is applied between the anode and cathode of the DO probe. When the O2 reaches the cathode, an electron is added to the O2 molecule, creating an electric current. It is this voltage that drives the O2 reaction and determines the DO concentration.