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DEX Dendrometers
for Stem & Fruit Growth
The DEX20, DEX70, DEX100 and DEX200 are highly precise electronic dendrometers that measure the growth and size of plant stems and fruits. The effects of environmental factors on the water balance of plants and stem size variations over time are easily monitored with a temperature compensated dendrometer. The DEX is a caliper-style device with a full bridge strain gage attached to a flexible arm. The output signal is then recorded by a datalogger or computer in real time. The millivolt sensor output shows both the diurnal and long term growth of the plant. The device has been used to test plants under conditions of water stress, elevated ozone and other atmospheric pollutants. Applications for screening plants for growth rate and stress tolerance are also common.
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Installation
The device is connected to a datalogger, clamped onto a stem and suspended
with mounting monofilament guides on the
center of gravity of each caliper arm which are then attached to the tree or a staked plant. Velcro straps are provided
for easy installation on trees or woody plants. The screw adjuster is tightened to adjust the clamping blocks on opposite
sides of the dendrometer. Thereafter the change in stem size increases the output, which directly converts to the diameter
increase past the point one recorded as the device's zero point.A calibration multiplier may be loaded directly into a
logger multiplier command, as well as the zero offset, and thus giving readings directly in mm or inches instead of millivolts. Users may install optional
shading and shielding to minimize heating and radiation effects.
Application
A field test was done in an apple orchard in Mattawa, Washington in September 1995. Data was collected over a 15 day period. After the data was acquired, the information was transferred to a personal computer for analysis. Millivolt signals were converted to millimeter units of movement. The initial value of the Dendrometer was then subtracted from subsequent values so that the Dendrometers were zeroed. The effect of temperature was removed by predicting the effect of temperature, then subtracting this value from the data points.
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