ADC in Digital Temperature Sensor DS18B20

sensortemperature

According to the datasheet of DS18B20 temperature sensor, it is clear that the sensor is digital so the output is in digital form.

The resolution of the temperature sensor is 9, 10, 11, or 12 bits, corresponding to increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C, respectively, and by default it is 12-bits. Which means, for 12-bits, a change of 0.0625°C in temperature causes an increment of 1-bit.

But there is no information given on how much change in voltage will result from a change in Temperature (i.e. scale factor).
For example, there is an analog temperature sensor in which a change of 10mV in the output voltage is equal to a change of 1°C of temperature.

Is there any way to calculate the scale factor of the digital temperature sensor like the way we do for analog?

Best Answer

All you really need to know is contained here: -

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Internally the device may have a sensor that produces 10uA per degree or 10mV per degree or it may be like a thermistor or RTD and vary its resistance to indictate temperature. This is Maxim IP and we are not allowed to know what method they use unless they tell us. If it's not in the data sheet then we cannot know - but you could assume it is one of the four methods I've mentioned and give details in your presentation of all ideas.

If you want to know the types of constant voltage or current sensors that could be used try looking up the AD590 (constant current at 10uA per degC) or the TMP36 (10mV per degC). I'm not aware of a particular name that describes the technology.

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Electronic – Using an LM34 temp sensor, how can I limit the range of temperatures

You don't limit what the sensor sees. The sensor reports what it sees. Your question is kind of like asking "I'm only interested in hot women. How can I adjust my eyes to not see ugly women?" You have no control over what the sensor sees.

Similarly, the ADC resolution (and sensor accuracy/resolution) will determine how fine-grained your temperature readings are, and how accurate they are. Generally this is never an issue unless you are specifically trying to save code or data space by looking only at 8 bits, for instance. Even in that case, you can always just read the upper 8 bits of the ADC (effectively making it an 8-bit ADC).

If you really feel you need to limit the range coming into the ADC, you can use an op-amp to shift and amplify the sensor signal so that 70-90 fits into 0-5 instead of the normal -55-150, but that's almost always not what you want to do because it's actually quite difficult to scale analog values without introducing noise or offsets.

It sounds like what you're after is something like this:

main_loop()
{
    while(1) {
        int temp;

        temp = read_temp();
        if (temp >= 85) {
            turn_fan_on();
        } else if (temp <= 80) {
            turn_fan_off();
        }
    };
}

You should add some code in there to only process that loop every second or so, and maybe check for out of range values to trigger an LED or something so you are informed when the sensor is detecting a bad condition. Maybe another check which reports a probable fan failure if the temp is above 95?

Sounds like a fun little project to get started with these concepts. Good luck!

Electronic – Pressure Sensor KP125, input Pressure to O/P voltage conversion,

See page 9 of datasheet. Its linear.

So, 115kpa - 40kpa = 75kpa range.

80kpa - 40kpa = 40kpa above minimum.

4.5v - .5v = 4 volt range.

So, 40kpa * 4v / 75kpa = 2.13v + .5v = 2.63v

Best Answer

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Electronic – Using an LM34 temp sensor, how can I limit the range of temperatures

Electronic – Pressure Sensor KP125, input Pressure to O/P voltage conversion,

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