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Author Topic: %mintemp% Sometimes Reports 0.0 Degrees Unexpectedly  (Read 277 times)

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Offline FPGAgeek

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%mintemp% Sometimes Reports 0.0 Degrees Unexpectedly
« on: August 23, 2017, 05:02:15 PM »
I have only seen this a handful of times where the daily low temperature is reported at 0.0-degrees Celsius (see attached) even though the graph and data log don't have equivalent data recorded. I think this spurious low temperatures also get logged in the monthly all-time low temperature records too as I currently have July (%recordlowtempjul%), August (%recordlowtempaug%) and September (%recordlowtempsep%) all of which reporting 0.0-degrees in 2016.

This is a similar to this discussion here: https://www.weather-watch.com/smf/index.php/topic,65482.0.html

I am not sure why this happens, is there anything I can do to test this further?

Any thoughts, thanks guys?

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Re: %mintemp% Sometimes Reports 0.0 Degrees Unexpectedly
« Reply #1 on: August 23, 2017, 08:40:48 PM »
what weather station type?

Offline FPGAgeek

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Re: %mintemp% Sometimes Reports 0.0 Degrees Unexpectedly
« Reply #2 on: August 23, 2017, 09:33:51 PM »
Davis VP2 connected via native RS232.

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Re: %mintemp% Sometimes Reports 0.0 Degrees Unexpectedly
« Reply #3 on: August 23, 2017, 09:41:02 PM »
it could be a periodic fault in the temperature sensor?
you could try setting a minimum temperature value limit in WD as a test (control panel, offsets, limits)

Offline FPGAgeek

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Re: %mintemp% Sometimes Reports 0.0 Degrees Unexpectedly
« Reply #4 on: August 24, 2017, 06:32:58 AM »
Yes it could be - what I will do then is tap off the received VP2 RS232 data to another computer such that I have the raw data logged if and when it happens again for comparison.

How does WD manage the samples from the VP2 regarding temperature i.e. are the high/lows compared against each sample received and the current temperature logged (per minute) an average of the samples received?

Thanks

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Re: %mintemp% Sometimes Reports 0.0 Degrees Unexpectedly
« Reply #5 on: August 24, 2017, 08:13:03 PM »
all the data received over a minute is averaged for the data/log file
but each data point received is used for the max/min of the day

Offline FPGAgeek

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Re: %mintemp% Sometimes Reports 0.0 Degrees Unexpectedly
« Reply #6 on: August 24, 2017, 08:36:29 PM »
That makes sense.

I will setup a RS232 logger connected to the VP2 data to see if I capture anything, I have only seen this 3x times (i think) before, this was last year so I am not sure if I will capture anything of interest but I will try.

Offline FPGAgeek

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Re: %mintemp% Sometimes Reports 0.0 Degrees Unexpectedly
« Reply #7 on: September 05, 2017, 07:21:34 PM »
I saw this issue again on Sunday at 00:26hrs. Unfortunately I hadn't setup my VP2 data capture  #-o I have definitely set it up now and its capturing all VP2 data transmitted from the console to the weather PC interface.

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Re: %mintemp% Sometimes Reports 0.0 Degrees Unexpectedly
« Reply #8 on: October 11, 2017, 05:58:40 PM »
So after quite a few days of logging Davis VP2 serial data using a standalone PC, I finally captured some data while a faulty 0.0-degrees (outside low temperature) was reported in WD.
 
Background
Note, this issue doesnít manifest itself often on my setup.
I logged all the data transmitted from the Davis VP2 console by picking off the data transmitted over the-wire i.e a second received copy of the data using a standalone PC.
The PC data logger date and time stamped the data received such that I could correlate the WD data with the captured VP2 data reception. I also checked that the two computer (WD and data logger) clocks were relatively synchronised for data correlation purposes - the logger was approx 20-seconds ahead.
The rogue temperature reading was recorded on 2017/10/08 04:12 local time by WD.
 
Update
Interestingly the Davis VP2 LOOP data around the time of occurrence (04:12 +/-2-mins) all report a temperature of 50.n-degrees with no rogue 0.0-degree readings. However one anomaly that can be seen in the data log at 04:13:13 is a pause in transmission of a LOOP response packet as shown below:

Code: [Select]
2017/10/08.04:13:11
4C 4F 4F 00 00 5E 09 59 75 9E 02 3F F5 01 02 03 | LOOP
2C 01 FF FF FF FF FF FF FF FF FF FF FF FF FF FF
FF 5E FF FF FF FF FF FF FF 00 00 00 00 00 00 00
FF FF 00 00 11 00 04 0A 00 00 28 00 BA 01 FF FF
FF FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 34 03 06 2C CE 02 25 07 0A
0D E5 D5

2017/10/08.04:13:13
4C 4F 4F 00 00 5E 09 59 75 9E 02 3F F5 01 02 03 | LOOP
2C 01 FF FF FF FF FF FF FF FF FF FF FF FF FF FF
FF 5E FF FF FF FF FF FF FF 00 00 00 00 00 00 00
FF FF 00 00 11 00 04 0A 00 00 28 00 BA 01 FF FF
FF FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 34 03 06 2C CE 02 25 07 0A
0D E5 D5                                        | LOOP (CRC=good)
06                                              | ACK (COMMAND)
4C 4F 4F 00 00 5E 09 59 75 9E 02 3F F5 01 02 03 | LOOP
2C 01 FF FF FF FF FF FF FF FF FF FF FF FF FF FF
FF 5E FF FF FF FF FF FF FF 00 00 00 00 00 00 00
FF FF 00 00 11                                  | LOOP halt

2017/10/08.04:13:14
               00 04 0A 00 00 28 00 BA 01 FF FF | LOOP continue
FF FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 34 03 06 2C CE 02 25 07 0A
0D E5 D5                                        | LOOP (CRC=good)

2017/10/08.04:13:15
4C 4F 4F 00 00 5E 09 59 75 9E 02 3F F5 01 02 03 | LOOP
2C 01 FF FF FF FF FF FF FF FF FF FF FF FF FF FF
FF 5E FF FF FF FF FF FF FF 00 00 00 00 00 00 00
FF FF 00 00 11 00 04 0A 00 00 28 00 BA 01 FF FF
FF FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 34 03 06 2C CE 02 25 07 0A
0D E5 D5

So it looks like the Davis VP2 concole paused transmission of a LOOP response packet for approx 1 to 2-seconds while it was servicing a higher priority interrupt possibly. Although I canít guarantee this because the PC logger is running under Microsoft Windows which is not an real-time operating system (RTOS) i.e. the pause may have been in the PC data logger. I will need to double check this for other occurrences in the logged data that I have.

If what I captured is a genuine pause of the VP2 console transmitting the LOOP response packet, could this be a possible cause for WD to log 0-degrees?

Thanks

 

cumulus