Lab Experiment 11
Introduction to CST-Motor Control Trainer. PRACTICE and observe the
behavior of different fundamental blocks:
A. Voltage to Frequency Converter
B. Frequency to Voltage Converter
C. Light intensity control using Driver (PWM method)
D. Photoconductive Cell (LDR)
Objective:
To introduce about Control System Trainer and demonstrate the use of its different modules.
Basic Theory:
A voltage-to-frequency converter (VFC) is an oscillator whose frequency is linearly proportional
to a control voltage. The VFC/counter ADC is monotonic and free of missing codes, integrates
noise, and can consume very little power. It is also very useful for telemetry applications, since
the VFC, which is small, cheap and low-powered can be mounted on the experimental subject
(patient, wild animal, artillery shell, etc.) and communicate with the counter by a telemetry link
as shown in Figure
There are two common VFC architectures: the current-steering multivibrator VFC and the
charge-balance VFC (Reference 1). The charge-balanced VFC may be made in asynchronous or
synchronous (clocked) forms. There are many more VFO (variable frequency oscillator)
architectures, including the ubiquitous 555 timer, but the key feature of VFCs is linearity—few
VFOs are very linear.
Apparatus Required
1- CST Trainer
2- Frequency Counter
3- Voltmeter
4- 2mm patch cords (3)
Procedure :
1- Make the connections according to Fig.
2- Connect CST trainer to AC mains.
3- Switch on the trainer by main switch.
4- Set the potentiometer in such a way that it gives 0.5V output at tp2 and measure the frequency
at tp3 using frequency counter.
5- Set the potentiometer in such a way that it gives 1.0V output at tp2 and measure the frequency
at tp3 using frequency counter.
6- Now repeat the step 4 and 5 for 1.5V 2V upto 5V and measure the frequency at tp3 using
frequency counter.
7- Switch off the power supply.
8- Make the table and plot a graph.
B- Frequency to Voltage converter
Objective :
The main objective is that Frequency to voltage converter converts the frequencies or pulses to
the proportional electrical output such as voltage or current.
Basic Theory :
It is an important tool for electromechanical measurements where repeated events are occurring.
So, when we provide a frequency across a frequency to voltage converter circuit, it will provide a
proportional DC output.
Apparatus Required :
1- CST Trainer
2- Frequency Counter
3- Voltmeter
4- 2mm patch cords (2)
Procedure :
1- Make the connections according to Fig.
2- Connect CST trainer to AC mains.
3- Switch on the trainer by main switch.
4- Set the clock frequency 5KHz and observe the voltage at socket 5 using Digital Voltmeter.
5- Tune the potentiometer and increase the colck frequency for every 5 KHz and observe the
change in voltage with respect to frequency.
6- Switch off the power supply.
7- Make the table and plot a graph.
C. Light intensity control using Driver (PWM method)
Objective :
The main objective is to explain several methods for applying additional PWM-based intensity
control to LED drivers. Several constant-current LED drivers, with or without builtin PWM,
serve as examples of the techniques.
Basic Theory :
Maxim Integrated Products provides many LED (light-emitting diode) drivers with PWM (pulsewidth modulation) intensity control for a wide range of applications. The intensity is normally
controlled by using the serial interface to send the LED driver a command to change the register
bits for the corresponding LED. The number of bits for intensity control ranges from 4 to 8 bits,
which corresponds to16 to 256 intensity levels. Intensity control for other Maxim LED drivers is
carried out by adjusting the amount of the constant-current sinking through an open-drain LED
port.
Apparatus Required :
1- CST trainer
2- 2mm patch cords (5)
Procedure :
1- Make the connections according to Fig.
2- Connect CST trainer to AC mains.
3- Switch on the trainer by main switch.
4- Slowly tune the potentiometer and observe the change in the intensity of the lamp 1.
5- Switch off the power supply.
D. Photoconductive Cell (LDR)
Objective :
The main objective is that Photoconductive cells function by receiving light energy, which in
turn frees electrons from their valence bonds in semiconductor material.
Basic Theory :
Photoconductive cells are light-sensitive resistors in which resistance decreases with an increase
in light intensity when illuminated. These devices consist of a thin single-crystal or
polycrystalline film of compound semiconductor substances. The most commercially available
are photoconductive cells, which are manufactured from cadmium sulfide (CdS), which is
sensitive to light in the visible spectrum. CdS photoconductive cells (CdS cells) are often
referred to as light dependent resistors (LDR). They function within the same general spectral
range as the human eye, and are therefore widely used in applications where this type of spectral
response is required.
Photoconductive cells function by receiving light energy, which in turn frees electrons from their
valence bonds in semiconductor material. At room temperature, the number of free charges in a
semiconductor is relatively limited, but the addition of light-released electrons raises
conductivity (and thereby reduces resistance). This change in resistance may be as large as
several hundred thousand ohms from a darkened state to only a few hundred ohms in sunlight.
Embedding the conductive path within the semiconductor substrate, in a zig-zag pattern, will
enhance the level of resistance. In addition to an increase in dark resistance, this same pattern
will reduce the current as well, changing the output current to about one milliampere (mA) per
lumen.
Apparatus Required :
1- CST trainer
2- Voltmeter
3- mm patch cords (4)
Procedure :
1- Make the connections according to Fig.
2- Connect CST trainer to AC mains.
3- Switch on the trainer by main switch.
4- Tune the potentiometer and set the 1V at tp15 and set the intensity of light w.r.t set voltage
and set voltage at socket 13.
5- Measure the output of photoconductive cell as indicated on digital multimeter.
6- Switch off the power supply.
7- Make the table and plot the graph.
Comments:
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