Moving-iron instruments are commonly used in laboratories and switch boards at commercial frequencies because they are very cheap and can be manufactured with required accuracy. Moving-iron instruments can be divided into two types: 1. Attraction type …. in which a sheet of soft iron is attracted towards a solenoid. 2. Repulsion type …. in which two parallel rods or strips of soft iron, magnetised inside a solenoid, are regarded as repelling each other.