Abstract: A device for measuring sap flow in a stem region comprises a rigid housing, configured like a clam-shell, and insulated and sealed from intrusion from radiation or water or weather by a collar which circumscribes the housing situated around the stem region being measured. Enclosed within this housing is a substrate preferably constructed from a composite of foam tape and rubber gasket material to provide a means for the electronics to conform to a diversity of stem cross-sections and irregularities. Temperature-sensing electronics measure energy transferred from an internal heater strip to the ambient, to the stem region, and to measure heat flowing up the stem. Heat transfer related to sap flow in a stem region is determined from four signals, two signals provided by two pair of differential thermocouples, a signal generated from a thermopile, and a signal indicative of the millivoltage delivered to the heater.

Abstract: A device for measuring the sap flow in herbaceous plants and trees directly without the necessity of an empirical calibration, using the heat balance method. A strap-on, removable, and reusable collar device powered by a 0.2 to 5.0 watt heater is abuttably affixed to the periphery of a stem or trunk. A plurality of temperature sensors are embedded in a weatherproof collar and shield assembly and are automatically processed by a small battery-operated recorder which also periodically stores in its memory the sap flow rate and the accumulated total thereof. These sap flow rate records may be obtained periodically for further analysis. A method is also provided for mass production thereof.