Attraction-type or single-iron type instruments are a category of electromechanical measurement devices commonly used in the field of measurement and instrumentation. These instruments are specifically designed to measure various electrical quantities, such as voltage, current, and power, based on the principle of electromagnetic attraction.
Here's how an attraction-type instrument works:
Basic Principle: The basic principle behind these instruments is the interaction between the electromagnetic field produced by the current being measured and the magnetic field generated by a permanent magnet or a coil. When current flows through a coil or a conductor placed in a magnetic field, a force is generated due to the interaction between the magnetic fields.
Components: An attraction-type instrument typically consists of the following components:
Coil: The coil is wound around a soft iron core, creating an electromagnet. When current passes through the coil, it generates a magnetic field around the iron core.
Permanent Magnet: A permanent magnet is positioned in proximity to the coil's iron core. The magnetic field produced by the permanent magnet interacts with the magnetic field generated by the coil.
Pointer: There's a pointer attached to the moving element of the instrument. The pointer moves in response to the force generated by the interaction between the magnetic fields.
Working: When current flows through the coil, the coil's iron core becomes magnetized and generates a magnetic field. This magnetic field interacts with the magnetic field of the permanent magnet, resulting in an attractive force between the two magnetic fields. This force causes the coil and the attached pointer to move. The extent of the movement is proportional to the strength of the current passing through the coil.
Measurement: The movement of the pointer is calibrated to indicate the magnitude of the electrical quantity being measured. By observing the position of the pointer on a scale, the user can determine the value of the measured quantity.
Attraction-type instruments have been widely used in various applications, including ammeters (to measure current), voltmeters (to measure voltage), and wattmeters (to measure power). They are relatively simple and robust devices but might have limitations in terms of accuracy, especially at high frequencies or when measuring rapidly changing values.
It's important to note that with advancements in technology, digital instruments like