The main Temperature and humidity sensor array for the weather station. In the background is the newly replaced Davis Vantage Pro2 all in one weather station with the black rain tipping bucket.
The temperature and humidity array consists of 4 calibrated platinum resistance thermometers (PRT) temperature sensors and two humidity sensors.
The PRT’s are rated at 1/3 DIN and a reference 1/10 DIN PRT, suppled and calibrated (April 2019) by Sterling Sensors to an accuracy of 0.07°C at 25°C. The humidity sensors (eBay) are outside calibration (October 2015), but claim an accuracy of ±0.8 %RH at 80 %RH at 23°C.
The temperature and humidity sensor are housed in METSPEC RAD10 radiation shields to shield the effects of solar heating. The Davis radiation shield is aspirated with a fan which turns on if the solar radiation reported is > 200 W/s and the wind speed is less than 4mph.
** The METSPEC radiation shields “seem” to over record temperatures in very bright sunshine – I am looking to ether fan aspirate the RAD10 radations shilds or relocate them into an aspirated Stevenson’s shield.
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The roof mounted wind direction and speed array. According to WMO guidelines, wind meassuring sensors should be mounted at 10 meters high, which they are. However, wind turbulence from the roof lessens the accuracy when the wind is coming from the West or South.
There are 4 wind sensors. The black one is for Davis VP2 weather station (ProData). The large “wind vane” is an RMYoung R5103 wind direction and speed which I used to take with me to measure wind speeds in hurricanes.
The least side sensor is a modern ultra-sonic anemometer my by Gill Instruments (eBay). It has no moving parts so will never wear out! The near silver cup anemometer is a first-class calibrated (Sep-2016) anemometer
by Vector Instruments (eBay) – I was really surprised to find such a highly accurate sensor to cheap! For wind speed and gusts, I take readings from the three sensors (not Davis) every second and then average them out over three seconds
to provide current wind speed. I then take a rolling 1 minute, 2 minute and 10-minute max wind speed to provide wind gusts data. Wind direction is averaged over 1 minute from the Ultrasonic and RM Young sensors.
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Rainfall is measured by a 0.1mm resolution SBS1000 WMO first class calibrated (April-2019) tipping bucket rain gauge supplied by EML Ltd. As raindrops fall into the xxx wide funnel collector,
they pass through and fall onto a small tipping bucket. When this bucket is full its tips, thus recording that 0.1mm of rain has fallen.
By measuring the time taken between tips (and some clever maths) the rain rate is calculated in mm/hour. The Davis VP2 rain collector is a 0.2mm device and it seems to under record rainfall by about 15%
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Measuring concreate surface temperature is an important consideration when calculating ground frosts and predicting black ice. I use a TP107 BetaTherm 100K6A1IA Thermistor supplied by Campbell Scientific (Shepshed) which as a temperature measuring range of -35° to +50°C and a survival range of -50°C to +100°C which is important
as in the summer, on a very hot day Solar radiation can heat the concreate slab to over 60°C. Often the concreate temperature can be below 0°C while the airtime is above freezing. This may then allows black ice to form on untreated roads.
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I use a TP107 BetaTherm 100K6A1IA Thermistor supplied by Campbell Scientific to measure Grass Temperature. Also shown is a grass minimum sensor for the Davis VP2 weather station.
The Grass Minimum Temperature is the temperature recorded in open air ground on short turf, with the tip of the thermometer just in contact with the tips of the blades of grass. It is also described as the temperature at 5cm (2in) above ground.
The grass minimum temperature often varies substantially from air temperature, which is measured at 2-meters above ground. Often the 2-meter air temperature can be +4°C, while the grass temperature can be below zero at -1 °C
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Close up of the UK and solar Sensors. solar panels power the weather station during the day.
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