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The SD-5M Sensor enables to monitor variations of stem diameter in micron range. Two phenomena affect diurnal behavior of stem diameter: growth and water balance of a plant. A growth component depends on a vegetation stage (see Fig.1 below). Two features of the daily stem variation curve are to be noted: daily contraction amplitude and daily maximums trend (see Fig. 2 below). Usual daily transpiration cycle produces a temporary reduction of water content in plants, which is manifested in the proportional reduction of stem diameter. In case of developing water deficit, the daily contraction amplitude increases. At the same time, a considerable water deficit may prevent a total replenishment of water reserves in plants during the night, resulting in downtrend of stem diameter maximums. Thus, the SD-5M sensor allows investigating intimate effects of environmental factors on water balance and growth of plants.


Fig.1. Greenhouse bell pepper: a typical seasonal growth curve of the stem base internode. Shown at the background of air temperature (AT) and vapor pressure deficit (VPD). Daily variations are indistinguishable in this large scale. 
Fig.2. Greenhouse tomato: During March 23-25, a lack of irrigation water caused both increase of daily contraction amplitude and even a negative turn of daily maximum trend (red line). 


The SD-5M Stem Microvariation Sensor includes a LVDT-based sensor mounted in special clip and a dc powered LVDT signal conditioner with optional power adapter for unipolar power supply. 


Linear Measurement Range: 0-5 mm
Diameter Range of Suitable Stems: 4 to 25 mm 
Output: 0-2 V or 4-20 mA (optional)
Output Temperature Coefficient: <200 ppm/?C FS
Supply Voltage: 15 Vdc 15%
Power adapter operates on 10 to 30 Vdc
Dimensions: 90 x 30 x 25 mm (sensor)
120 x 70 x 37 mm (signal conditioner)