How to design corrosion sersors ？

This is a method for investigating electrode reaction mechanisms by analyzing the response of a metal (electrode) to sinusoidal alternating current. The equivalent circuit for a rust layer consists of polarization resistance, solution resistance, and double-layer capacitance. While this method indirectly calculates corrosion rates via polarization resistance, the reliance on proportionality constants derived from anodic and cathodic polarization curves leads to significant error margins. Consequently, direct calculation methods are preferable when assessing corrosion rates or the extent of corrosion. Once the current density is determined, Faraday's law can be applied to calculate the corrosion rate.

The electrical resistance method is one approach for directly calculating the extent of corrosion; it converts the increase in electrical resistance caused by corrosion into a measure of corrosion loss. Sensors utilizing this method are referred to as ER (Electrical Resistance) sensors. Due to concerns regarding corrosion monitoring and waterproofing, this method has not historically been applied to assess the corrosion behavior of steel in outdoor atmospheric environments.
Discrepancies exist between the corrosion measurements obtained by ER sensors and those from standard corrosion test coupons in high-salinity environments. This is because, in such environments, the sensing element undergoes localized pitting corrosion—with pits approximately 0.5 to 1.0 mm in diameter and 250 µm deep—that can penetrate the sensor. This significantly increases the resistance in the affected area, causing it to dominate the total resistance and thereby impairing sensor performance. Since this localized corrosion is a result of the atmospheric environment itself, eliminating it would alter the very conditions being studied; therefore, we are refining the sensor concept to prevent localized corrosion from affecting the total resistance, even if pitting occurs.
Modifying the sensor geometry offers a solution to this issue by minimizing the impact of localized corrosion within the measurement zone.
We are continuously working to improve the accuracy of corrosion sensors by mitigating the influence of localized corrosion on average corrosion measurements. We welcome discussions with peers regarding the precision of corrosion rate measurements.