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Help - Question fluctuation in sensor when untouched

 
 
Dani101
 
Reply Sat 14 Oct, 2017 08:00 pm
Could someone please explain the possible reasons why the ambient temperature reading may fluctuate even though the temperature sensor is left untouched, Assuming that the room’s temperature has reached equilibrium and at a stable temperature.
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Type: Question • Score: 0 • Views: 1,722 • Replies: 9
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cameronleon
 
  1  
Reply Sat 14 Oct, 2017 08:27 pm
@Dani101,
It could be tolerance +- calibrated on device

Size of room, temperature outside the room, Number of windows. Size of windows. Door? Sealed doors? Your question is not given much information to find possible causes.
Dani101
 
  1  
Reply Sat 14 Oct, 2017 08:35 pm
@cameronleon,
Unfortunately, it is all the information I have been given :/ thank you for your help though
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Dani101
 
  1  
Reply Sat 14 Oct, 2017 08:38 pm
@cameronleon,
If it helps, they said to look at a datasheet for the temperature sensor DS18B20. However, I haven't seen any connections thus far from it.
0 Replies
 
centrox
 
  1  
Reply Sun 15 Oct, 2017 05:24 am
Size of fluctuations?
Fluctuation frequency?
Dani101
 
  1  
Reply Sun 15 Oct, 2017 06:31 am
@centrox,
I haven't been given that information it literally says "Explain the possible reasons why the ambient temperature reading may fluctuate even though the temperature sensor is left untouched. We assume that the room’s temperature has reached equilibrium and at a stable temperature. Hint: search on the internet for the datasheet for the temperature sensor DS18B20."
centrox
 
  1  
Reply Sun 15 Oct, 2017 06:33 am
So this is your schoolwork, and you don't know how to do it? Have you studied the datasheet?
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centrox
 
  1  
Reply Sun 15 Oct, 2017 07:05 am
I am not familiar with this particular chip, but I do know that small fluctuations, especially in the least significant bit of the output data, can be caused by noise on the DC supply line. or the signal line.
0 Replies
 
cameronleon
 
  1  
Reply Sun 15 Oct, 2017 10:29 pm
@Dani101,
Quote:
...for the temperature sensor DS18B20


Maybe this message is late, but after you provided the additional information I checked online some places with a possible answer.

https://www.reddit.com/r/AskElectronics/comments/3tuzcz/ds18b20_temperature_sensor_is_fluctuating_when_in/

DS18B20 Temperature sensor is fluctuating when in low temperatures

Quote:
Could be due the the element heating itself up....


The answer given above has lots of troubleshooting guides in the thread.

https://forums.adafruit.com/viewtopic.php?f=19&t=60581

The script is run every two minutes and seems to work well, however at some point in the early morning the readings fluctuate wildly going up or down 3-5 degrees. Has anyone experienced this. The connections seem fine.

Quote:
...is moisture / high humidity affecting it, ie, the pins being connected via moisture?


Also lots of suggestions following the answer considering moisture as the reason for fluctuation.



0 Replies
 
Blickers
 
  1  
Reply Wed 18 Oct, 2017 10:56 pm
There's also this from the datasheet:
1. The use of parasite power is not recommended for temperatures above +100°C since the DS18B20 may not be
able to sustain communications due to the higher leakage currents that can exist at these temperatures. For applications in which such temperatures are likely, it is strongly recommended that the DS18B20 be powered by an external power supply."


Note the question said the temperature in the room is stable, it didn't say it necessarily under 100 degrees C. It also didn't say the room is in a residential home and not some factory or lab. If you hook the unit up using parasitic power, which it is built to function on only under 100 deg C, then you can get variations.

2. There is also a variation for the device as well:

https://i.imgur.com/IxbCcnS.png
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