Bug Filed on 04-14-2016: Erroneous temp reading leads to graph clutter


#1

What dashboard are you using? (Web, iOS, Android)
Web


What OS? (Jessie, Wheezy)
Jessie


What Model Pi?
B+


Please describe the bug / issue. Attaching any relevant screenshots would be very helpful!

The the temperature coming from DS18B20 has been read as impossibly low at one point for some reason (-723 Celcius). This leads to a very high spread of values along the Z-axis on the week graph as show below:

The graphs for the last 10 minutes, hour and day reads as normal since the time for the extreme reading has passed on those graphs.
Adjusting the slider value (which was blank) to -10 and 60 did not correct the issue for the graph back in time, but might do so for future readings.


#2

It keeps happening after setting slider values. I guess a quick fix to this would be to filter out the values that are outside the range of the slider values.


#3

Is there a reason you can think of where the DS18B20 sensor might have been disconnected during that time period? Large negative values are almost always a result something happening with the wiring.


#4

Well there could be something faulty with the sensor, but the wiring is pretty solid. As you can see, it reads the temperature corrently almost all the time. But just one wrong reading messes up the graph. It’s located in a shipping container that I enter very rarely, and the errors always occured when I’m not present.


#5

Yes I see, it’s just weird that it randomly shows up intermittently.

@eptak Any ideas on why there could be random erroneous temp. reading on the DS18B20?


#6

how is connected the sensor ? directly on Raspberry Pi GPIO ?
GPIO based implementation of 1-Wire has not an industrial grade on Raspberry Pi.
It can be improved by using an 1-Wire master controller connected via I2C.

also, 1-Wire reading sometime provides error, and driver currently returns very negative value in that case.


#7

We pushed a fix for this issue. Let us know if it persists??

Thanks @vegetish !

Cheers,

-B