Sometimes gives unrealistic values for temperature

[153957]

The weather daq should return -999 in case there is an error in the measurement.

But this does not always happen and sometimes unrealistic data gets into the datastore.

Here is an example of bad data:
http://data.hisparc.nl/django/show/stations/501/2012/5/9/
http://data.hisparc.nl/django/show/stations/501/2012/5/3/

There we suddenly see values like -18222.2226562 °C

If this is actually bad data or some error, then the weather daq should return -999, as error code.