A galvanometer is an electromechanical instrument used for detecting and indicating an . Strip chart recorders with galvanometer driven pens may have a full scale frequency response of Hz and several centimeters of deflection. A chart recorder is an electromechanical device that records an electrical or mechanical input trend onto a piece of paper (the chart). Chart recorders may record. Galvanometer Type Recorder:The D’Arsonval movement used in moving coil indicating instruments can also provide the movement in a Galvanometer Type.
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The pointer deflects when current flows through the moving coil. The deflection of the pointer is directly proportional to the magnitude gakvanometric the current flowing through the coil.
As the signal current flows through the coil, the magnetic field of the coil varies in intensity in accordance with the signal.
Chart recorder – Wikipedia
The reaction of this field with the field galvanometruc the permanent magnet causes the coil to change its angular position.
As the position of the coil follows the variation of the signal current being recorded, the pen is accordingly deflected across the paper chart. The paper is pulled from a supply roll by a motor driven transport mechanism. Thus, as the paper moves past the pen and as the pen is deflected, the signal waveform is traced on the paper.
The recording pen is connected to an ink reservoir through a narrow bore tube. Gravity and capillary action establish a flow of ink from the reservoir through the tubing and into the hollow of the pen. Because of the compact nature of the galvanometer unit or pen motor this type of recorder is particularly suitable for multiple channel operation. Hence it finds extensive use in the simultaneous recording of a large number of varying transducers outputs.
This recorder uses a curvilinear system of tracing. The time lines on the chart must be arcs of radius R where R is the length of the pointerand the galvanometer shaft must be located exactly at the center of curvature of a time line arc.
Galvanometer Type Recorder
Improper positioning of the galvanometer or misalignment of the chart paper in the recorder can give a distorted response, i. One method of avoiding the distorted appearance of recordings in curvilinear coordinates is to produce the recording in rectangular coordinates.
In this design, the chart paper is pulled over a sharp edge that defines the locus of the point of contact between the paper and the recording stylus.
The stylus is rigidly attached to the galvanometer coil and wipes over the sharp edge as the coil rotates. In one of the recordersthe paper used is usually heat sensitive, and the stylus is equipped with a heated tip long enough to guarantee a hot point galvanoemtric contact with tecorders paper, regardless of the stylus position on the chart.
Alternatively the paper can be electrically sensitive, in which case the stylus tip would serve to carry current into the paper at the point of contact. These moving galvanometer type recorders are comparatively inexpensive instruments, galvanlmetric a narrow bandwidth of 0 — 10 Hz.
They have a sensitivity of about 0. In most instruments, the speed of the paper through the recorder is determined by the gear ratio of the driving mechanism. If it is desired to change the speed of the paper, one or more gears must be changed. Some recorders contain a timing mechanism that prints a series of small halvanometric along the edge of the paper chart, as the paper moves through the recorder.
This time marker produces one mark per second. These types of recorders are mostly used as optical recordersand contain a light source provided by either an ultra violet or tungsten lamp. A small mirror is connected to the galvanometer movement and the light beam is focussed on this mirror, as shown in Fig. The beam reflected from the mirror is focussed into a spot on a light sensitive paper.
As the current passes through the coil, the mirror deflects. The movement of the light beam is affected by the deflection of the small mirror, and the galvanoetric on the paper also varies for the same reason, thus tracing the waveform on the paper.
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