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A strip chart recorder records the variations of a quantity with respect to time while a X-Y recorder is an instrument which gives a graphic record of the relationship between two variables.
In strip recorders, usually self-balancing potentiometers are used. These self-balancing potentiometers plot the emf as a function of time. In X-Y recorders, an emf is plotted as a function of another emf. This is done by having one self-balancing potentiometer control the position of the rolls. while another self-balancing potentiometer controls the position of the recording pen.
In some X-Y recorders, one self-balancing potentiometer circuit moves a recording pen in the X direction while another self-balancing potentiometer circuit moves the recording pen in the Y direction at right angles to the X direction, while the paper remains stationary.
There are many variations of X-Y recorders. The emf, used for operation of X-Y recorders, may not necessarily measure only voltages. The measured emf may be the output of a transducer that may measure displacement force, pressure, strain , light intensity or any other physical quantity. Thus with the help of X-Y recorders and appropriate transducers, a physical quantity may be plotted against another physical quantity.
Hence an X-Y recorder consists of a pair of servo-systems, driving a recording pen in two axes through a proper sliding pen and moving arm arrangement, with reference to a stationary paper chart. Attenuators are used to bring the input signals to the levels acceptable by the recorder.
This figure shows a block diagram of a typical X-Y recorder. A signal enters each of the two channels. The signals are attenuated to the inherent full scale range of the recorder, the signal then passes to a balance circuit where it is compared with an internal reference voltage. The error signal the difference between the input signal voltage and the reference voltage is fed to a chopper which converts d.c signal to an a.c signal. The signal is then amplified in order to actuate a servometer which is used to balance the system and hold it in balance as the value of the quantity being recorder changes. The action described above takes place in both axed simultaneously. thus we get a record of one variable with respect to another.
The use of X-Y recorders in laboratories greatly simplifies and expedites many measurements and tests. A few examples are being given below