Galvanometer Type Recorders

Galvanometer Type Recorders Points : Galvanometer Type Recorders, Definition These recorders use a D. Arsonval galvanometer. The pointer is equipped with a recording pen mechanism (stylus). As the current flows through the coil, it deflects. The greater the amplitude of the incoming signal (which is proportional to the quantity being measured), the greater is the deflection. When the pointer comes to rest on account of controlling torque exerted by springs, the stylus also comes to rest. Thus, the value of the quantity is recorded. This is necessitated by the fact that in recorders, the movement of the instrument requires an appreciable torque. To obtain this torque the galvanometer movement consists of a large moving coil situated in a strong magnetic field.

It should be understood that the instrument must be critically damped or nearly critically damped so that there is no significant overshoot. This type of recorder is not useful for recording fast variations in either current or voltage or power. This records only the average values and hence it should be designed for these.

It is a modified version of the Permanent Magnet Moving Coil (PMMC) instrument. The modification is done in order that the chart may be driven at a constant speed by a clockwork mechanism or an electric motor. The type of chart used depends upon the form of movement. The recorder under consideration uses a chart having a curvilinear system of tracing. This system is used because it allows the direct use of simple moving coil movement. However, some instruments employ additional linkage system in the system which allow the use of rectilinear system of tracing.