Specific FAQs on Weather Monitor II type stations

Note

This page deals with questions specific to the Weather Monitor II and Wizard III stations. Answers to many of the more general questions will be similar to those in the VP FAQ section and we suggest that you also look there to see if there is a relevant answer.

WMII and WWIII FAQ

1. The station is recording erroneously low minimum temperature values. What's the problem?

This is usually a symptom of noise on the electrical mains supply to the station, although it can also be caused by a nearby source of radiofrequency interference causing through-space interference. (For some reason, temperature seems to be the parameter that is most sensitive to this problem, even though other parameters could in principle be affected). Typically what happens is that a burst of interference or noise passes into the console from the mains supply and causes a momentary error in temperature value. Even though the interference may be of very short duration, the aberrant low temperature value induced may be recorded as a new low value and will therefore show up as the minimum value for that day. If it is possible to connect the station temporarily (eg for a few days) to a 12v battery such as a car battery rather than the mains and the problem disappears then this is diagnostic of mains noise being the cause. Note that the internal backup battery is designed to power the station for a few hours only and so isn't suitable for this test. Also be very careful to observe correct polarity when connecting an external battery.

The solution is to try to identify the source of the interference or mains noise. Usually it turns out to be another item of office or household electrical equipment, often plugged into a mains outlet close by the outlet used for the console mains adapter, and can be anything that can generate interference. It could be any switch that is switching a significant electrical load, eg a timer or thermostat in a heating circuit, or an electrical motor, especially an ageing one that might have dirty brushes, or eg a fluorescent desk lamp. The noise may only be generated when the device is switching on or off. Sometimes the cure may be as simple as moving the console and source of interference to different electrical ring circuits. But other times it may be difficult to identify the culprit definitively and the best solution may then be to obtain a mains smoothing adapter for the console mains supply, as are widely sold now for PCs. Be sure to look for one that is clearly marked as offering RFI (radiofrequency interference) suppression and not only anti-surge.

2. I'm not happy that my rain-gauge is measuring accurately. How can I check?

Please see the corresponding answer in the Vantage Pro FAQ.

3. How can I measure two external temperature values, eg air and ground temperature?

This is not possible with the standard station. However, the WMII station was designed to measure two temperature values: internal and external. Frequently the internal temperature is of little interest and it is possible to modify the station such that the internal temperature circuitry is actually connected to a second external sensor, using one of the standard Davis temperature sensors, eg #7817 or #7818. It is important to note that while that while this modification is eminently feasible (and indeed is described by Davis - see Application Note 17 - 'Extending Inside Temp Sensor' which is downloadable from the  Application Note area on the Davis website) it does involve working inside the console case. Officially this would invalidate the Davis warranty and therefore is recommended only for units outside their initial 12 month warranty period. It is possible to log this second temperature value to a PC using the standard Weatherlink software, but in this case the second external value will still nominally be labelled as inside temperature in some software packages.

4. Can I add a sunshine sensor to a Weather Monitor II station?

Sorry, but no. The new Vantage Pro range of Davis stations is designed to accept a solar radiation sensor, but the older WMII station was not designed to do so. Davis certainly do supply an optional solar radiation sensor (eg #7821) but this is only intended for fitting to VP stations.

It is perhaps worth mentioning that standalone sunshine sensors are available from makers other than Davis. If you can find one of these that has its own independent PC input plus software to generate a PC-format image (ie gif or jpg) and if you are also using one of the third-party software packages such as Weatherview32 or Virtual Weather Station that allow external images to be included in their displays then it should be possible to include additional sunshine data in a PC display whose primary data is derived from a WMII station.