Module thermometer, temperature meter for digital multimeter using the ic lm35
Converser of temperature tension. To be used with a digital multimeter with reach from -40°C to 110°C. With checker of the state of it laughed and a without any adjustment, thanks to LM35!
curiosity about the temperature in centigrades grados and the celsius
The ice is founded the 0°C and the point of ebullition of the water, at sea level it is of 100°C. Using those two point of reference is gauged the temperature scale quickly. When I speak to °C it is degrees Celsius and not centigrade as we can see in some literatures. Centigrade it is a scale of 100. While temperature is going besides 100. Then the correct is to speak degrees Celsius! Good it arrives of blá blá…
Today thanks to the circuit integrated specialized of National Semiconductor, denominated LM35, we didn’t need of nor a calibration to obtain the correct temperature.
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Circuit of the thermometer with lm35
For the circuit we needed a battery of 9v and of a tension of negative feeding. Obtained according to the datasheet of LM35 by the Diodes D2 and D3. The resistor R5 allows the tension of exit of the sensor to be negative in relation to mass of the multimeter so that she can measure resistances below 0°C. The resistor R4 desaclop the exit of the probe in relation to exit of high impedance of the multimeter. The circuit based on the transistor Q1 serves as device of control of the feeding tension and of proof of the state of the battery. When closing the key S1, The led will light informing that the tension of the battery is above 7V, that is necessary for the correct operation of the circuit.
LM35 should be set up in a metallic tube from about 5 to 10 CM, linked to the main circuit through a cable trifler of at the most 1 m of length. The tube should be closed tightly on the two sides to allow the measure of liquids.
it/you appeases main and the battery should be placed in a box of plastic small. The plate should be isolated of the battery to avoid short circuit and damages caused by the corrosive content of the battery.
à·à should use I find connected in the box for connect with the multimeter.
Operation mode for the circuit:
Before doing a temperature measure it tests the pile pressing S1, everything ok is enough to connect the unit to the multimeter to accomplish the measures. In agreement with the temperature the multimeter in the scale of Volt DC 10V will indicate a tension from -4 to 1,1V or in the scale from 2000mV -400 to 1100mV, that depends on the multimeter, that tension corresponds the temperature from -40 to 110°C. In the first case the decimal point will be despised and in the another it increases a decimal point after the third digit. With time it becomes used to.
Example 0,256V (256mV) = 25,6°C -0,158V (-158mV) = -15,8°C. LM35 provides a lineal exit of +10mV/°C.
Suggestion of printed circuit board for the assembly
Side of the components for the lm35
Components for the assembly the circuit
- R1 = 330Ω
- R2,R3 = 100kΩ
- R4= 1kΩ
- R5= 18kΩ
Capacitor electrolytic
- C1= 10µF/12V
Semiconductors:
- D1,D2= 1n4148
- L1= Led Red
- Dz1= 4v7/400mW
- T1= bc547
- IC1= lm35
Several:
- S1 = Switch, Jacques banana male or similar, clip for battery, etc.
