Showing posts with label Temperature. Show all posts
Showing posts with label Temperature. Show all posts
Monday, October 20, 2014
Fan Speed Control for Temperature Circuit Diagram
With this simple circuit that you will be able to control the speed of a DC fan according to the temperature measured by a temperature sensor. It is an ideal accessory for your projects that require cooling that are not constant.
This simple design allows precise speed control of motors, fans, and blowers, proportional to the temperature. An NTC thermistor (R1) is used as temperature sensor. A circuit optional was added to remotely monitor the operation of the fan and to allow some kind of indication of the approximate speed by increasing the brightness of an LED.
Fan Speed Control for Temperature Circuit Diagram
The R5 must be configured to allow the engine just starting to run at the desired temperature. Any 6K8 between the NTC thermistor 22K can operate provided that the R2 value is one tenth of the thermistor. R6, R7 and D1 are optional: R7 obligation is adjusted until the LED glow dimly when the engine is just running.
Parts List
R1 15K @ 20 ° C NTC Thermistor (See Notes)
R2 1K5 1/4W Resistor (See Notes)
R3 1K 1/4W Resistor
R4 270R 1/4W Resistor 1/2W
R5 22K Trimpots
R6 680R 1/4W Resistor (Optional, see Notes)
R7 470R Trimpots
C1 100μF 25V Electrolytic Capacitor
LED D1 (Optional, any shape and color, see Notes)
Q1 BC547 45V 100mA NPN Transistor
Q2 BD140 80V 1.5A PNP Transistor
M1 Fan Motor 12V 700mA max.
R1 15K @ 20 ° C NTC Thermistor (See Notes)
R2 1K5 1/4W Resistor (See Notes)
R3 1K 1/4W Resistor
R4 270R 1/4W Resistor 1/2W
R5 22K Trimpots
R6 680R 1/4W Resistor (Optional, see Notes)
R7 470R Trimpots
C1 100μF 25V Electrolytic Capacitor
LED D1 (Optional, any shape and color, see Notes)
Q1 BC547 45V 100mA NPN Transistor
Q2 BD140 80V 1.5A PNP Transistor
M1 Fan Motor 12V 700mA max.
Sunday, September 21, 2014
Thermistor Temperature Monitor Circuit and explanation
Thermistor Temperature Monitor Circuit and explanation
This sensor circuit uses an ordinary NTC thermistor with a resistance of 47k at room temperature. A suitable part from Maplin Electronics is FX42V. The circuit is set in balance by adjusting the the 47k potentiometer. Any change in temperature will alter the balance of the circuit, the output of the op-amp will change and energize the relay. Swapping the position of the thermistor and 47k resistor makes a cold or frost alarm.
At room temperature (25 degrees Celsius) a 47k NTC thermistor resistance is approximately 47k. The non-inverting op-amp input will then be roughly half the supply voltage, adjusting the 47k pot should allow the relay to close or remain open. To calibrate the device, the thermistor ideally needs to be at the required operating temperature. If this is for example, a hot water tank, then the resistance will decrease, one way to do this is use a multimeter on the resistance scale, read the thermistors resistance and then set the preset so that the circuit triggers at this temperature.
Please note that if the temperature then falls, the relay will de-energize. If the environment temperatures changes rapidly, then the relay may chatter, as there is no hysteresis in this circuit.
Hysteresis, allows a small amount of "backlash" to be tolerated. With a circuit employing hysteresis, there will be no relay chatter andthe circuit will trigger at a defined temperature and require a different temperature to return to the normal state. Hysteresis can be applied to the circuit using feedback, try a 1 Mega resistor between op-amp output, pin 6 and the non-inverting input pin 2 to give the circuit hysteresis.
Without offset null adjustment, the output of the 741 IC will be around 2 Volts (quiescent) swinging to nearly full supply when triggered. The 4.7k and 1k resistor form a potential divder so that under quiescent conditions the transistor will be off. Quiescent or steady state means no signal, or in this case (when the temperature does not cause the output to swing to full voltage).
Source: Temperature Monitor
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