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Old 11-25-2009, 10:38 PM
ronnierohan007 ronnierohan007 is offline
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Default Basic temperature control project

hi i was stuck with this temperature control project and i was wondering if anyone is willing to help me with it.. here is the description

PROJECT "T" Temperature Control
Description: An industrial process requires a specified temperature controlled by a thermostat.
Temperature is to be increased by an electric heater, and decreased by natural heat transfer to the
ambient environment. (Extra credit for adding cooling by a fan in addition to natural cooling.)
(a) First design the temperature measurement system. Temperature is sensed using the varying
resistance of a thermistor. Measure voltage drop across the thermistor and convert it to a binary
number using Analog- Digital conversion and digital display of relative temperature.
(b) Design the temperature control system to have three levels (warm, hot, very hot). The
temperature is to be controlled from the breadboard. Apply the binary number from the A/D
converter to a Comparator. Compare the measured temperature to a reference. If the temperature
is too high, turn the heater off. If the temperature is too low, turn the heater on. The temperature
will vary somewhat between off and on, but the thermal inertia will keep the temperature
approximately constant at the desired setting. You will need a "logic amplifier" consisting of a
BJT transistor with the base connected to the output of a logic gate as the control input,
responding to the comparator. The BJT collector is connected to +5V via the magnetic coil of a
relay. The relay contacts connect the heater-resistor to the power supply when the transistor
turns on the current to the relay coil. Power for the heater (a 10 ohm, 10 watt power resistor, with
a thermistor glued to it to sense the temperature) is supplied at 5 volts from the bench power
supply. (The system can be cooled more rapidly by a small fan on the shaft of a motor connected
to the same power supply and controlled by another relay).
(c) Draw a functional block diagram showing the temperature measurement and control system.

it would be awesome if if you guys can help me calculate resistor values and give me a circuit diagram for the same.. your help is really really appreciated.
i can provide a basic block diagram if you guys need it.
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Old 11-25-2009, 11:37 PM
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mik3 mik3 is offline
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I don't think you need to make any calculations because it says to draw a functional block diagram. I think it only wants the idea of the circuit represented by function blocks.
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Old 11-27-2009, 01:10 AM
ronnierohan007 ronnierohan007 is offline
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hey thanks for the reply but thats a project i need to complete and i have to get the circuit ready soon. I'd really appreciate all the help.
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Old 11-27-2009, 03:13 AM
Arm_n_Legs Arm_n_Legs is offline
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You can try using the LM35 for measurement of the temperature. This simple device output 10mV/C. Feed this signal to one input of the comparator. The other input can be derived from a resistor network to provide the voltage for comparison.
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Old 11-27-2009, 03:19 AM
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SgtWookie SgtWookie is offline
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The design requirements state that a thermistor is to be used.
An LM35 is an IC, not a thermistor. While it is very convenient and very linear, it would not be within the design requirements.

Since this appears to be a homework/class/course assignment, it should be in the Homework Help forum.
General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input.
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Old 11-27-2009, 10:41 PM
ronnierohan007 ronnierohan007 is offline
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yeh we need to use a thermistor. can any1 give me a basic idea what do do here! and calculations would even more helpful.
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