X-Y Recorders
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.
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:
Speed torque characteristics of motors
lift Drag wind tunnel tests
Plotting of characteristics of vaccum tubes, zener diodes rectifiers
and transistors etc
Regulation curves of power supplies
Plotteing stress-strain curves, hysteresis curves and vibrations
amplitude against swept frequency
Electrical characteristics of materials such as resistance versus and
temperature plotting the output from
electronic calculators and computers
STRIP Chart Recorders
Magnetic tape recorders
The magnetic tape is made of a thin sheet of
tough plastic material; one side of it is coated
with a magnetic material (iron oxide). The
plastic base is usually polyvinyl chloride (PVC).
Recording head, reproducing head and tape
transport mechanism are also present.
The recording head consists of core, coil and a fine air
gap of about 10 micrometer. The coil current creates a
flux, which passes through the air gap to the magnetic
tape and magnetizes the iron oxide particles as they
pass the air gap. So the actual recording takes place at
the trailing edge of the gap.
The reproducing head is similar to that of a recording
head in appearance. The magnetic tape is passes over a
reproducing head, thereby resulting in an output
voltage proportional to the magnetic flux in the tape,
across the coil of the reproducing head. Thus the
magnetic pattern in the tape is detected and converted
back into original electrical signal.
The tape transport mechanism moves the
tape below the head at constant speed
without any strain, distortion or wear. The
mechanism much be such as to guide the tape
passed by the magnetic heads with great
precision, maintain proper tension and have
sufficient tape to magnetic head contact.
