Sap Flow Meter (SFM1)  is a discrete standalone instrument based upon the Heat Ratio Method. This measurement principle has proven to be a robust and flexible technique to measure plant water use; being able to measure high, low, zero and reverse flows in a large range of plant anatomies & species from herbaceous to woody, and stem sizes > 10 mm in diameter.

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The theoretical basis and ratiometric design of the Heat Ratio Method makes possible the measurement of high, low, zero and reverse flows.

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The SFM1 Sap Flow Meter consists of two temperature sensing needles arranged equidistance above and below a central heater. These needles are inserted into the water conducting tissue of the plant by drilling 3 small parallel holes. Heat is then pulsed every 10 minutes into the water conducting tissue of the plant. The heat is used as a tracer to directly measure the velocity of water movement in the plant stem. The Heat Ratio Method does not require insulation. 

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The SFM1 Sap Flow Meter is a dedicated self-contained  data logger, with a heater and two temperature sensing needles, that provides power to the heater and logs sap flow in litres per hour of water used by the plant. This is the water actually used by the plant in litres, completely independent of any water that may have been lost to evaporation from bare soil, run off or through drainage.