ACM Corrosion sensors

This type of sensor is used to assess corrosion in high-humidity atmospheres, salt-spray environments, or areas of high humidity beneath low-temperature insulation. It
consists of two dissimilar metals that are electrically insulated from each other.
Condensation and rainfall can bridge the gap between the substrate layer and the conductive layer. When a conductive path forms, an electric current is generated due to the
potential difference between the two metals, leading to corrosion of the substrate. This corrosion current can be measured and analyzed, allowing for a quantitative
assessment of the corrosivity of the installation environment. Because the distance between the two metals is very small, a water film forms easily under conditions of high
humidity or condensation. Corrosion occurs not only in liquid solutions but also in atmospheric environments; the sensor effectively simulates the condensation caused by physical phenomena in high-humidity conditions, which can otherwise lead to corrosion issues.

Can integrate temperature and humidity sensors.

How it works

1. Corrosive gases and moisture reach the silver probe
The sensor is exposed to the surrounding air. Pollutants such as H₂S, SO₂, chlorine compounds, NOx, together with humidity, can react with the metal surface.

2. The silver surface slowly corrodes
For a silver corrosion sensor, corrosive gases can form compounds such as silver sulfide (Ag₂S) on the surface. The amount/rate of surface reaction is related to the corrosiveness of the atmosphere.

3. The sensor measures the change continuously
Instead of taking an air sample every few minutes or hours, the corrosion element is monitored continuously. The electronics detect the very small change in the probe's electrical characteristics as corrosion develops.

A simplified concept is:

Corrosive atmosphere → chemical reaction on Ag probe → change in electrical property → electronic measurement → corrosion rate

4. The system calculates corrosion severity
The measured corrosion response can be converted into a corrosion rate, typically expressed in Ångström per unit time or another standardized corrosion-rate metric.

5. It evaluates the environment against ISA-71.04 classifications
The resulting corrosion information can be used to assess the environmental severity:

The classification is generally evaluated over a rolling 30-day period, rather than simply looking at one instantaneous reading.

Why use a silver probe?

Silver is particularly useful because it reacts sensitively with certain atmospheric contaminants, especially sulfur-containing gases. A high-purity silver element provides a controlled and repeatable surface for corrosion measurement.

One important clarification: “Sterling Silver, purity 999” is technically contradictory. Sterling silver normally means about 92.5% silver (Ag 925), whereas 999 silver means 99.9% silver (fine silver). If the product specification says “solid Sterling Silver, purity 999,” I would recommend verifying the manufacturer's intended material designation.

real-time

It does not mean the sensor can instantly know the final 30-day G1/G2/G3 classification. Rather:

Continuous probe measurement
↓
Continuous accumulation of corrosion data
↓
Corrosion-rate calculation
↓
Rolling 30-day assessment
↓
G1 / G2 / G3 / GX classification

This is particularly useful in data centers, telecom facilities, control rooms, semiconductor facilities, substations, and other mission-critical environments, where a short-lived increase in corrosive contamination can be detected rather than waiting for a periodic sampling cycle.

Scope of Application
This standard applies to:

Process control systems (DCS, PLC, etc.)
Measuring instruments
Analytical equipment
Electronic equipment installed in control rooms and in the field
Printed circuit boards and electronic components