LM35 Analog Temperature sensor Transducer of automatic Furnace control

 3 TEMPERATURE SENSOR LM35 
LM35 Analog Temperature sensor is the Transducer of automatic Furnace control, which actually senses the Temperature of the cavity of the furnace. Here we will discuss the LM35 analog temperature sensor in more detail, as compared to other post or projects on this web blog.temperature sensor using 8051 and adc

3.1 General Description of LM35 analog temperature sensor

The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has an advantage over linear temperature sensors calibrated in ° Kelvin, as the user is not required to subtract a large onstant voltage from its output to obtain convenient Centigrade scaling. The LM35 does not require any external calibration or trimming to provide typical accuracies of ±14°C at room temperature and ±34°C over a full -55 to +150°C temperature range. Low cost is assured by trimming and calibration at the wafer level. The LM35’s low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus andminus supplies. As it draws only 60 µA from its supply, it has very low self-heating, less than 0.1°C in still air. The LM35 is rated to operate over a -55° to +150°C temperature range, while the LM35C is rated for a -40° to +110°C range (-10° with improved accuracy). The LM35 series is available packaged n hermetic TO-46 transistor packages, while the LM35C, LM35CA, and LM35D are also available in the plastic TO-92 transistor package. The LM35D is also available in an 8-lead surface mount small outline package and a plastic TO-220 package.

3.2 Features of LM 35 Analog sensor:
Calibrated directly in ° Celsius (Centigrade)
Linear + 10.0 mV/°C scale factor
0.5°C accuracy guaranteeable (at +25°C)
Rated for full -55° to +150°C range
Suitable for remote applications
Low cost due to wafer-level trimming
Operates from 4 to 30 volts
Less than 60 µA current drain
Low self-heating, 0.08°C in still air
Nonlinearity only ±14°C typical

Low impedance output, 0.1 ohmfor 1 mA load

To Interface with Microcontroller 8051, still we need two more stages in which operational amplifier and analog to digital converter are involved. So we can say that between lm35 and microcontroller 8051 two more components exists. In the comming posts we will discuss the opAmp and then ADC. In our project we have used the 741 operational amplifier as an inverter, that is, an inverting amplifier with unity gain. In this chapter we review some types of operational amplifiers commonly used.

Suppose that we power an op-amp with +15V & -15V, tie the inverting to the ground, and apply a signal of + 0.01V dc to the noninverting input. The op-amp will attempt to amplify this signal by 100000 and produce the result on its output that may be predicted as 100V. The maximum positive voltage, the op-amp output can go to, however, is a volt or two less than the positive supply voltage, so this is as for as it goes. Generally the op-amp output goes into saturation at about 13V. Now if we apply -0.01V to the noninverting input then output will try to go to -100V as fast as it can. The output, however, goes into saturation at about -13V, so it stops there.lm35 interfacing with 8051


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