Davis UV Sensor

[asprey]

Over the last couple of months I've been watching my UV Sensor, and it goes from 0.0 straight to 0.5, then 0.6, 0.7 etc.,

On the reverse of this (when coming down) it goes 0.7, 0.6, 0.5 and then straight to 0.0.

So it misses everything in between 0.0 and 0.5 in both directions.

Is this correct?  Is there an adjustment on the Davis console that I can amend to rectify this?

I thought I'd ask here first (before going to Davis), as I always get a speedy reply    

[_Niklas_]

Im also having issues with this. Does anyone know if this is is how the sensor is supposed to work ?

Niklas

[prodata]

Is this correct?

This is correct - ie there's nothing wrong with operation of the sensor.

The problem as I understand it is that the signal from the UV sensor is relatively weak (solar UV is not an easy parameter to measure accurately)  and it's difficult to define a true 0.0 dark reference value that will be stable long-term in the face of sensor ageing/drift, noise etc.

Before the 0.5 fix was applied, Davis were getting recurrent fault reports from dissatisfied users that UV sensors were reading non-zero values overnight. Such were the extent of the complaints that Davis decided that the only solution was to treat 0.5 Index as the lowest non-zero reading that could be reasonably guaranteed to be a true reading irrespective of noise, age of sensor and hence set 0.5 as the lowest non-zero value that would display. (IIRC there were earlier trials that tried eg a 0.3 threshold value and some older firmware may still allow such readings, but I can't fully remember the details here.)