This application is a ternary application for the determination of both the acid cocentration HCl and the salt concentration FeCl₂. Ferric chloride is a product that is formed during the etching process of steel. About 99% of the ferric chloride being formed is FeCl2.

The analyser 9570 uses a ultrasonic and a conductivity sensor to determine both concentrations.
Because of the interest in iron rather than ferric chloride, the concentrations are expressed in terms of grams of iron per litre liquid.

The accuracy for both readings is about 3 g/l over the entire range. For specific applications, requiring high accuracy in a limited range, the accuracy can be approved to better than 2 g/l.