Hello OWFS-developers,
I am experiencing delays and also time-outs when reading temperatures of
very very close to and equal to 85 degrees Celsius.
I am using a BananaPI with a LinkUSB as hardware.
As software I am using on the system side owserver 3.1p1-6 and on the
application side python together with pyownet as client to owserver.
I have 25 DS18B20, which are powered.
My application is a heating system, where a wood burning oven heats up
two 800l buffer containers of water to a max temperature of 95 degree
Celsius.
Every 30s simultaneous is written, followed by a two second wait, before
starting reading back the temperatures sequentially. The time for an
average read of one sensor is about 0.2 seconds at maximum resolution. I
am monitoring the time of each read and when the read exceeds 0.25
seconds I log this.
Additionally every read I do with pyownet is used with a time-out of 1s,
meaning, if after 1 second owserver did not reply a value, I abort and
go to the next sensor.
When the buffers get slowly discharged, the temperature of the sensors
at the buffers slowly drifts to the 85 degree mark.
*Here is the thing**:*
While slowly drifting towards the 85 deg C mark, at first the sensor
takes longer to read. The read time is then typically around 0.75s. That
happens for a couple of cycles, before then the reading times out -
longer than 1s, in which case the read is aborted and the next sensor
gets read. It can alternate between time-out and elongated reading time.
When a temperature is read, it is 85.0 something or later 84.9
something. After a while the reading is back with longer reads, Finally
everything is back to normal and the temperature is below 85 degrees C.
That happens successively for all the 10 sensor (5 at each buffer in
various hights) .
I am aware that the 18S20 did report an error with 85 deg C, but the
18B20 should not do this.
Is there something in owfs that would re-read in case a value of exactly
85 deg C would be returned by a sensor?
Or is it the LinkUSB that is the culprit.
Does anybody else experience the same phenomenon?
Cheers Martin
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