Definition of Recorder – A recorder is a measuring instrument that displays a time-varying signal in a form easy to examine, even after the original signal has ceased to exist.
Recorders generally provide a graphic recod of variations in the quantity being measured, as well as an easily visible scale on which the indication is displayed.
The variety of recording instruments in the central monitoring and control stations of many industrial and utility plants is proof of their importance in industrial work. They provide a continuous, written record of the changes taking place in the quantity being measured. This chart record may be scaled off in electrical values (mV/mA) or in terms of some non-electrical quantity, such as temperature or pressure.
Many recording instruments include an additional provision for some sort of controlling action. If the control function is the primary one, the measuring instrument is called a controller.
The recorder usually provides an instantaneous indication for monitoring at the same time as it makes a graphic record.
Electronic recording instruments may be divided into three groups.
The easiest type is simply a meter having an indicating needle and a writing pen attached to the needle. If a strip of paper is pulled at a constant velocity under the writing pen (at a 90° angle to the direction of pen motion), the moving pen plots the time function of the signal applied to the meter. A highly special designed D’ Arsonval movement is used to drive the writing pen. This type is called a galvanometer recorder.
Another recorder is the null or potentiometric recorder, operating on a self-balancing comparison basis by servomotor action. This recorder is basically a voltage responsive positional servo system using a motor to move a writing device back and forth across a piece of paper. The servo system can be made extremely accurate, rugged and powerful.
The magnetic recorder is the third type. In it, a thin magnetic tape or wire, is magnetised in accordance with a varying signal as the tape passes rapidly across a magnetic recording head. The frequency response of magnetic recorders can extend from 0 Hz to a few kHz to nearly 10 MHz. Because of the wide bandwidth of tape recorders, several modes of recording (direct, FM and digital) can be used.
There are two types of recording devices,
(i) Analog, and
Analog recorders may be
(i) graphic or
Graphic recorders are devices which display and store a pen and ink record of some physical quantity.
They are of three types
(i) strip chart recorder,
(ii) circular chart recorder, and an
(iii) X-Y recorder.
These and other types of recorders are discussed in detail in the following sections.