Temperature Sensor circuit LM35

LM35DZ is a small temperature sensor components such as transistors (TO-92). The components are very easy to use is able to measure the temperature to 100 degrees Celsius. With a scalable voltage output linear with measured temperature, which is 10 millivolts per 1 degree Celsius, then the component is suitable for use as a friend to our experiments, or even for applications such as digital room thermometer, pasteurization machine, or digital body thermometer.

LM35 can be supplied with voltage from 4V-30V DC with 60 mikroampere drain currents, have high levels of self-heating effects of low (0.08 degrees Celsius), and including our close relatives, our wallets.

self-heating is the heating effect by the component itself as a result of the work flow through it. For the temperature sensor components, these parameters must be considered and diupakara or at-handle well because this can cause measurement error. As the temperature sensor type PT100 RTD or PT1000 for example, this component should not be excited by currents exceed 1 miliampere, if exceeded, the sensor will experience self-heating that causesthe results of measurement is always higher than the actual temperature .

For more details about the characteristics of the LM35 temperature sensor, then you can download the datasheet using the link below.

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Figure in addition to the right is a schematic drawing a series of basic-DZ LM35 temperature sensor. The circuit is very simple and practical. Vout is the sensor output voltage is linearly scalable to the measured temperature, which is 10 millivolts per 1 degree Celsius. So if Vout = 530mV, then the measured temperature is 53 degrees Celcius.Dan if Vout = 320mV, then the measured temperature is 32 degrees Celsius. This output voltage can be directly fed as input into such signal conditioning circuit operational amplifier circuit and filter circuit, or other circuits such as voltage comparator circuit and a series of Analog-to-Digital Converter.

Basic circuit is sufficient to simply experiment or for applications that do not require perfect accuracy of measurement. But not for a real application. Evident from the experiments I have done, the sensor output voltage is not yet stable. At relatively the same temperature conditions, if I change the supply voltage change (I raise or lower), then Vout also changes. Indeed, this logic seems correct, but for this instrumentation is not allowed. Compared with the level of precision, the accuracy rate is the primary measuring tool for measuring tool should to be standard for all its users. If the value fluctuate relative to the condition that no change, then such a measure can not be used.

To improve the performance of basic circuit above, then added a few passive components as shown in the picture below.

Two 150K resistors that diparalel diseri forming a 75K resistor with a capacitor 1uF. The series RC-Series is a recommendation from the manufacturer LM35. While the 1K5 resistor and capacitor form a series 1NF passive low-pass filter with a frequency of 1 kHz. Filter output voltage is then fed into the no-reverse voltage amplifier with amplification factor can be adjusted using variable resistors.

With this circuit, the output voltage of this circuit proved far more stable than the output voltage above basis. Thus the accuracy of measurement has to be improved. Opamp output voltage can be directly fed into the ADC circuit and then the data is further processed by the microcontroller.

Tips
To further improve the accuracy and precision temperature measurement, it is necessary for setting the optimal ADC reference voltage is used so if you use 8-bit ADC for example, then the range 0-255 must represent the minimum and maximum temperatures can be measured by temperature sensor circuit. Do not give the wrong reference voltage at the ADC circuit, so the range of the ADC exceeds or is less than the input voltage range.

The next step, do pensamplingan at least ten data and compute the average rating. This average value is used as the measurement results. If necessary, it can also be applied to digital filter algorithm to obtain the final result of measurement is really accurate.