Saturday, 16 August 2014

High Temperature Alarm using NI MYDAQ

Present days detection of high temperature is important in industrial applications and also in some of the daily home applications .For knowing temperature and give an alarm for high temperature of  water, welding purposes, furnaces etc. So here I present a high temperature alarm circuit using LM 35.
Let us first discuss on LM35 which I used in this application
 LM35  whose output voltage is varied linearly with repect to temperature, but inversely proportional to the temperature.
Detectable range:-55 deg.C to 150 deg.C.  

1) LM35 temperature sensor.
3) connecting wires.
Circuit which is interfaced with NI MYDAQ:
Here +15 is connected to +VCC of LM35 and, AGND of DAQ to ground and output terminal to AI +1 and AI-1 to ground

First calibrate output voltage to the detected temperature using multiplier and adder.

Output displaying temperature:
Using comparator set a reference value:
Example: reference is 40
Temperature is 30. Then led is off (Boolean).
Here I used green one. But it would be better if we use red for danger.
Output when reference is more than detected temperature:
Output of  buzzer when reference is more than detected temperature.
Output when reference is less than detected temperature:
Example: if reference value is 20
Detected temperature is 30
If we observe here led is glowing.i.e., representing more temperature.

Output of buzzer when reference is less than detected temperature:
If any queries, post a comment as well as you can contact me at