Principle of dissolved oxygen electrode (reproduced in Baidu literature)

Dissolved oxygen electrode is based on the polarographic principle of the determination of dissolved in the liquid oxygen of the current-type electrode, the common dissolved oxygen analyzer used diaphragm electrode as a transducer, the dissolved oxygen concentration (actually oxygen pressure) converted into electrical signals, and then amplified, adjusted (including salinity, temperature compensation), by the analog-to-digital conversion display.

1. There are two types of membrane electrodes for the determination of dissolved oxygen: polarographic (polarography) and primary battery type (galvanic cell).

Polarographic (polarography): In the electrode, the Gold (Au) Ring or PT (PT) Golden Circle as the cathode; silver-silver chloride (or mercury-mercuric chloride) as anode. The electrolyte is potassium chloride solution. The outer surface of the cathode is covered with a layer of oxygen permeable film. The film can be made of PTFE, polyvinyl chloride, polyethylene, silicone rubber and other breathable materials. The polarization voltage between the two electrodes is applied 0.5~1.5 volts. Some polarization voltage is 0.7 volts.

Primary battery Type: The cathode is usually composed of precious metals, such as platinum, gold or silver, and the anode is composed of lead. In the presence of electrolytes such as KCL or lead acetate, PbCl2 or PB (AcO) 2 is formed, and the primary battery-type electrode does not require an external voltage. The reduction current at 28 ℃ is 5-25μa, therefore, the use of a dedicated circuit amplifier can be directly connected to the whole 5 or ten MV of the automatic potential difference recorder.

2. Principle: When dissolved oxygen through the film to reach the gold cathode surface, the following reaction occurs on the electrode. Cathode is restored: o2+h2o+4e→4oh-

At the same time, the anode is oxidized: 4CL-+4AG-4E→4AGCL
Under normal conditions, the i∞ value of the diffusion current generated by the reduction-oxidation reaction is proportional to the dissolved oxygen concentration (PS: The current generated by the metal ions that are diffused from the solution body to the electrode surface in the polarographic analysis). The following formula can be used to indicate:
I∞=NFA (pm/l) Cs
In the formula: i∞-steady State diffusion current
N-Gain Electronic number
F-Faraday constant (96500 coulomb) A-cathode surface area (square centimeter) pm-membrane permeability coefficient (cm 2/sec) L-thin film thickness (cm) cs-dissolved oxygen concentration (ppm)
When the electrode structure and the film are determined, the formula A, Pm, L, n, etc. are constant. k= NFA (pm/l), in the formula: I∞=KCS.
Therefore, the concentration of dissolved oxygen can be measured as long as the diffusion current i∞ measured. To eliminate the effects of temperature, salinity and barometric pressure, each model product is compensated by its own technology.

Principle of dissolved oxygen electrode (reproduced in Baidu literature)