Toheli

Technical information

The chambers are planned and constructed by Topi Pohja. They are made of transparent PMMA (acryl). Thickness of the sides and UV-permeable cover is 6 mm and 3mm, respectively. The chamber is 250 mm in height of which 70 mm is aluminum collar.  The ground area of the chamber sides is 250 mm times 200 mm and it is open towards the ground. Seal is rubber (sienikumi).

Operation of each chamber is controlled with microcontroller box (by Heikki Laakso). The chamber opens and closes by a gear motor (hammasvaihdemoottori)* with circa 4 rounds per minutes or by compressed air (2009->). In 2009, the chamber has been programmed to be closed for 3½ minutes every 30 minutes. Earlier, the chamber was mostly closed for the 3½ minutes but stayed opened thereafter for 30 minutes. The controller gives sign whether the chamber is closed or open. The state is found from the data file.

The system uses 12 VDC. The need for currency is circa 300 mA in motion and 20 mA immobilized.

In the chambers, there is a fan with a diameter of 25 mm and air temperature measurements. Vaisala CARBOCAP® Carbon Dioxide Probe GMP343 (Vaisala Oyj, Vantaa,Finland) enters the chamber through a hole on one of the sides. The measurement signal is automatically corrected for temperature but the oxygen, pressure and moisture corrections are turned off. (Pressure affects the oxygen correction.) Therefore, the concentrations must be corrected afterwards according to Vaisala classified equations. The probes has been calibrated circa once a month. In 2008 there were some technical difficulties and all of the sensors were sent to maintenance during which all the versions were updated from v4 to v7. New versions have been in use from the beginning of 2009. Notice, that there is a slightly different correction equations for the different versions

There is a varying set of other measurements too depending on year and chamber. Usually they are having an air moisture measurements (xx) and radiation sensors (Li-Cor 190SZ and Photosiodes xxx). The exact set of measurements can be concluded from the diaries (.txt) and dutyinfo\fileinfo.xls (sheets ToHeLi_1-2 and ToHeLi_3).