Vigyan Prasar is engaged in the development
of new training modules/methodologies/ equipment/ devices
for S&T communication. Scientific Experiments
using Computer
is a novel effort to explain to the students how computer
is useful in measuring and controlling physical parameters
and processes. VP has conducted a number of demonstrations
and workshops to explain how experiments on measuring and
controlling parameters like temperature, intensity of light
and sound, humidity etc. could be taken up to illustrate
use of computer in a variety of processes.
Can
one use a computer as a multi-meter? Or say as a thermometer?
Scientific Experiments using Computer is a software
and hardware interface that has been developed by Vigyan Prasar
to do that and much more. Through this interface not only
can one measure common physical parameters like temperature,
light or sound intensity, relative humidity, etc., using a
commonly available computer but also control a few parameters
so that it remains within the set value.
A student usually looks at
a computer as an upgraded typewriter or a device like television
with Internet access. School students of classes V –
XII write reports, browse the Internet, play computer games
and also do a little bit of programming, often without knowing
how that is useful! All students know that computer is very
powerful – it can be used to navigate the space shuttle, or
control sophisticated machines/processes. However, most of
them do not have any idea about how computers do it.
 Controlling any process do
require measurement of a few parameters like temperature,
light, humidity, etc., and taking appropriate measure based
on the comparison between the set value and the measured value.
For example, if measured temperature is more than the set
value then a heater can be turned off. Scientific Experiments
using Computer is an effort to explain to students how
a computer is useful in measuring physical parameters and
thereby controlling a process by feedback mechanism.
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How it works
 Any
physical stimulus like temperature, sound/light intensity,
etc., is first sensed by suitable sensors. Sensors produce
an output voltage, which is comparable to a physical stimulus.
Output of the sensor is fed into the Analog-to-Digital Converter
(ADC). The output of the ADC is digital, suitable to be
fed into the computer through a parallel port.
The digital value thus received
is processed by the computer, which produces the output.
The output is in two forms – first, it displays the value
of the physical stimulus on the computer screen, and second,
it sends command as a feedback signal. This feedback signal
is able to switch ON/OFF an electronic switch. The second
form of output is important for process control. The computer,
based on the comparison between the received value and the
set value, generates this feedback signal.
Let temperature of a process
need to be monitored and to be controlled within a set value.
An electrical heater is the temperature source for the process.
Here, a temperature sensor continuously senses the temperature
and the computer displays the value. If the received value
is within the set value, the computer will send a 0 (Zero)
– Logical False – as feedback signal, and the heater
switch will be ON. The moment the received value exceeds
the set value, the computer will send 1 (One) – Logical
True – as feedback, which would trigger a relay and
switch off the heater. The computer will keep on sending
1 as long as the received value exceeds the set value and
the heater would be switched off. After sometime, eventually
received value would be within the set value and the computer
would send 0, which would turn on the heater through the
relay. This closed loop monitoring would continue as long
as the monitoring and controlling of the process is required.
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The interface has two components
– hardware interface and software interface. Both the interfaces
work in tandem. Hardware interface consists of ADC, electronic
switch and sensors and is connected to computer through standard
parallel port. The interface enables one to read a physical
stimulus through sensors, convert it to digital form before
feeding it into the computer and operate the switching circuit
based on the instructions received from the computer.
Different sensors are used to sense different stimuli. Sensor
converts the stimulus to a corresponding voltage level. Higher
the intensity of the stimulus, higher is the output voltage
generated by the sensor. However, the relation is not always
linear. Non-linearity or exponential relation between input
and the output parameters can be taken care of at the time
of data processing by the computer. The output voltage is
converted to digital form by ADC. One 8-bit ADC is used in
the interface. Any input voltage is converted into a 8-bit
combination.
The switching circuit consists of transistors and solid-state
relays (SSRs). Transistors are turned ON or OFF, based on
the control bit received from the computer. The transistors
in turn operate the relays. The relays are connected to external
devices, which can be turned ON or OFF so that the measured
value remains within the set value. The SSR is able
to handle high current and voltage so that external devices
like heaters and lamps can be connected to the standard power
line through the relays. Relays are operated by electromagnetic
induction. Therefore, there is no direct contact between the
hardware interface and the external power line (in India standard
household supply is 230 volts, 50 Hz).
The software interface is the controlling unit, which processes
all the input data received from the hardware interface. Digital
data (Byte) is compared with the set value and control bit
is generated and sent to the hardware interface to turn ON
or OFF the switching circuit. The user can sit in front of
the computer and can control the entire process by selecting
the required sensor and setting the upper and lower limit
of the parameter. Once the parameter is set, the feedback
control continuously receives the data through the hardware
interface and compares it with the set value. This can continue
indefinitely without any human intervention. The software
interface also plots real-time graph and stores all the data
in database. These data can be retrieved any time for possible
data analysis.
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Possible
experiments with the present set up:
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Experiments on Temperature
n
Measuring ambient temperature
n
Measuring and controlling temperature of any process
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Experiments on Light
Intensity
n
Measuring brightness level of a room (LUX)
n
Measuring and controlling light intensity of any process
l
Experiments on Humidity
n
Measuring humidity of any place
n
Measuring and controlling humidity of any process
l
Experiments on Sound Intensity
n
Measuring sound intensity
n
Measuring sound intensity and feedback control
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Experiment on pH
n
Measuring pH of any liquid
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Oscilloscope
– Limited Applications
n
Time period/frequency of input waveform
n
Amplitude of input waveform
n
Polarity checking
l
Multi-meter – Limited Applications
n
Measuring voltage
n
Measuring
resistance
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n
Temperature sensor: Thermistor (Thermally sensitive resistors)
type
n
Light intensity sensor: LDR ( Light Dependent Resistors)
n
Sound intensity sensor: Microphone
n
Humidity sensor: Capacitor type – Dielectric of the capacitor
changes with humidity, thereby changing capacitance
n
pH sensor: Capacitor type.
n
Opto-coupler: Infrared emitter (Diode/Transistor) and receiver
(Transistor)
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How to
start
Any standard computer can be
used for the purpose. Install the software in the computer.
Follow simple instructions when installation is in progress.
Once software is installed, connect the interface unit to
the parallel port [also known as the line printer terminal
(LPT) Port] of the PC. Connect sensors in the slots provided
with the hardware interface.
Applications
Senior secondary
science students can do physics and computer based experiments
using this interface. As all the measured data is stored,
one can analyse the data for a definite period of time. The
interface provides scope to add new sensors and testing the
same.
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