WO2019126100A1

WO2019126100A1 - Single-board tree sap flow sensor

Info

Publication number: WO2019126100A1
Application number: PCT/US2018/066129
Authority: WO
Inventors: Taylor Scott JONES
Original assignee: President And Fellows Of Harvard College
Priority date: 2017-12-19
Filing date: 2018-12-18
Publication date: 2019-06-27

Abstract

A sap flow measurement device includes an elongate circuit board having a proximal end and a distal end. One or more downstream temperature sensors are disposed along a length of the circuit board. One or more upstream temperature sensors are disposed along the length of the circuit board parallel to the one or more downstream temperature sensors. One or more heating elements are disposed along the length of the circuit board parallel to and in between the downstream and upstream temperature sensors.

Description

SINGLE-BOARD TREE SAP FLOW SENSOR

Inventor: Taylor Scott Jones

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of ET.S. Provisional Patent Application serial number 62/607,379, filed December 19, 2017, entitled“SINGLE-BOARD TREE SAP FLOW

SENSOR,” which is incorporated by reference herein in its entirety.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under Grant No. 2017-67003-26487 awarded by the United States Department of Agriculture, and Grant No. 70NANB17H030 awarded by the National Institute of Standards and Technology. The government has certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates to measurement of a fluid. In particular, the present invention relates to a device for measuring sap flow in a tree.

BACKGROUND OF THE INVENTION

Trees generate biomass by the process of photosynthesis, which turns carbon dioxide, sunlight, and water into hydrocarbons. The rate of biomass creation of a tree, known as the “productivity” of the tree is a quantity of interest for scientists studying plant physiology, ecology, and global and local carbon cycles.

One way to measure productivity is to measure the rate of water consumption of the tree. Water is moved from the roots of the tree to the leaves (where photosynthesis occurs) in the form of sap. As such, studying the movement and dynamics of sap throughout a plant is one tool to understand productivity. Thermodynamic based methods utilize heat to quantify the rate at which sap (and, thus, water) passes through the xylem tissue of a plant. Such methods and systems are relatively simple and, thus, are commonly used. As shown by FIG. 1 A, one such system 100 for measuring sap flow involves the insertion of three probes 110, 112, 114 into the tree 120, parallel to the ground. A central probe 112 contains a resistive heater, and the other probes, temperature probes 110, 114, contain temperature sensors. A voltage pulse is applied to the heater creating a heat pulse. This heat is thermally diffused by the wood of the tree 120, and the impulse response is recorded by a data logger attached to the temperature probes 110, 114. In addition to heat transfer by diffusion, flowing sap in the adjacent wood advects some of the heat from the pulse downstream. This means that the rate of sap flow may be inferred from the difference in heating between the upstream and downstream sensors. Temperature sensors can be placed at multiple depths into the temperature probes 110, 114, which allows for the measurement of sap flow in different depths into the wood.

While the system 100 provides a mechanism for sap flow measurement, there are some problems with the system 100 that limit its usefulness and accuracy. For one, the probes 110,

112, 114 are difficult to build. In particular, tiny thermocouples or thermistors must be correctly attached to small stainless steel tubes. The probes 110, 112, 114 are also very difficult to install correctly into the tree 120. In order to insert the probes 110, 112, 114 into the tree 120, a long and thin drill bit is used to create the three holes, for example, a drill bit on the order of 65 mm long and 2 mm in diameter. Even utilizing a good jig mounted to the tree 120, the drill bit has a tendency to stray from the target course as it enters the tree, resulting in a non-parallel orientation of the probes (e.g., see FIG. 1B). It is very difficult, and typically not possible, to determine from the outside of the tree 120 how skewed the holes (and thus the probes 110, 112, 114) are. Because the accuracy of the alignment of the probes 110, 112, 114 within the tree and the spacing between the heater and sensors is critical to the reliability of the measurement, accuracy and correct interpretation of the data is impaired with the currently available systems. Therefore, there is a need for improved devices and methods for measuring sap flow.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a device for measuring sap flow in a tree. In particular, the present device comprises a circuit board having temperature sensors and heating elements disposed along a length of the circuit board. Sap flow may be measured by inserting the sap flow measurement device into a slot formed in the tree.

According to one aspect, the present invention provides a sap flow measurement device comprising an elongate circuit board having a proximal end and a distal end, one or more downstream temperature sensors disposed along a length of the circuit board, one or more upstream temperature sensors disposed along a length of the circuit board parallel to the one or more downstream temperature sensors, and one or more heating elements disposed along a length of the circuit board parallel to and in between the downstream and upstream temperature sensors.

Embodiments according to this aspect can include one or more of the following features. A microcontroller may be removably attached to the proximal end of the circuit board and may be configured for logging data from the one or more upstream and downstream temperature sensors and controlling the heating elements. A plurality of heating elements may be disposed along a length of the circuit board, where adjacent heating elements are spaced apart at equal intervals along the circuit board. A plurality of downstream temperature sensors and a plurality of upstream temperature sensors are disposed along a length of the circuit board, wherein adjacent downstream temperature sensors are spaced apart at equal intervals along the circuit board, and wherein adjacent upstream temperature sensors are spaced apart at equal intervals along the circuit board. Each of the one or more heating elements may be disposed in alignment with downstream and upstream temperature sensors. The downstream and upstream temperature sensors may be in alignment with alternating heating elements. The downstream temperature sensors may be spaced apart from the heating elements at approximately the same distance as the spacing between the upstream temperature sensors and the heating elements. The upstream temperature sensors may be disposed closer to the heating elements than the downstream temperature sensors are disposed from the heating elements.

Other systems, methods and features of the present invention will be or become apparent to one having ordinary skill in the art upon examining the following drawings and detailed description. It is intended that all such additional systems, methods, and features be included in this description, be within the scope of the present invention and protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principals of the invention. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. In the drawings, each like component is referenced by a like numeral. For purposes of clarity, every component may not be labeled in every drawing. In the drawings: FIG. 1 A is a schematic diagram illustrate a conventional sap flow sensor consisting of two temperature probes and one heater probe.

FIG. 1B is a schematic diagram of the sap flow sensor of FIG. 1 A with skewed installation of the probes.

FIG. 2 schematically illustrates an exemplary embodiment of a sap flow sensor in accordance with an embodiment of the present invention.

FIG. 3 is a schematic of the sap flow sensor of FIG. 2 as installed in a tree sensor in accordance with an embodiment of the present invention.

FIG. 4A schematically illustrates a slot in a tree for insertion of a sap flow sensor in a tree according to an embodiment of the present invention.

FIG. 4B shows the placement of the circuit board of FIG. 2 within the slot of FIG. 4 A.

FIG. 4C depicts a wound created by the slot of FIG. 4 A closing around the sap flow sensor eventually reaching a steady state.

FIG. 5 is a schematic diagram illustrating an example of a system for executing functionality of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

FIGS. 2-3 show an exemplary embodiment of a sap flow sensor 200 in accordance with the present invention. The sap flow sensor 200 is configured for measuring sap flow through the heat pulse velocity method, particularly utilizing a heat pulse method. The exemplary embodiments of the present invention provide a sap flow measurement device comprising a circuit board having a plurality of downstream sensors aligned along a length of the circuit board, a plurality of upstream sensors aligned parallel to the downstream sensors, and a plurality of heating elements positioned parallel to and in between the downstream and upstream sensors. Sap flow may be measured by inserting the sap flow measurement device into a slot formed in the tree. The sap flow measurement device may further be provided with a connector that is attachable to a microcontroller for logging data and controlling the heating elements.

As shown in FIG. 2, the sap flow sensor 200 includes a circuit board 212 configured to physically support one or more heating elements 214, one or more downstream temperature sensors 216a, and one or more upstream temperature sensors 216b. The circuit board 212, for example, a printed circuit board (PCB), may be substantially flat as illustrated, and includes one or more electrical conductors and all other necessary elements coupled thereto to provide the electric energy necessary to drive the heating elements 214 and temperature sensors 216a, 216b.

As illustrated, the circuit board 212 is an elongate structure which is generally rectangular in shape, having a proximal end 218 and a distal end 220. In use, the distal end 220 is inserted into a slot formed in the trunk of a tree to the appropriate depth. When properly inserted, a portion of the proximal end 218 extends outside of the tree trunk (e.g., as shown in FIG. 3). A microcontroller 310 may further be connected to the proximal end 218 of the circuit board 212 for logging data and controlling the heating elements 214. For example, the microcontroller 310 may be attachable to the circuit board 212 to provide T4ike shape as depicted in FIG. 2. The present invention is not limited as such, however, and any shape or interconnection design for the microcontroller 310 may suitably be used. As shown, one or more heating elements 214 are disposed along a length of the circuit board 212. One or more downstream temperature sensors 2l6a are provided parallel to the one or more heating elements 214, and one or more upstream temperature sensors 2l6b are also provided parallel to the one or more heating elements 214 so that the one or more heating elements 214 are sandwiched between the downstream and upstream temperature sensors 216a, 2l6b.

The heating elements 214 and the temperature sensors 216a, 216b can be virtually any kind of conventional heating elements and temperature sensors. For example, some exemplary heating elements 214 can include chip resistors or polymide heaters. Some exemplary

temperature sensors 216a, 216b can include chip thermistors or thermocouples. An exemplary embodiment of the current invention uses small (e.g. SMD resistor package imperial code 0402) thermistors for the temperature sensors and a set of 12 chip resistors (e.g., SMD resistor package imperial code 0805) in series as the heating element(s). However, a variety of types of heaters and temperature sensors could be used, provided they are robust enough to withstand outdoor temperatures and can be protected from moisture. A current embodiment of the invention uses a thin (2 mil) plastic sheath around the circuit board to protect the circuitry from moisture.

As depicted in FIG. 2, a plurality of heating elements 214 are disposed longitudinally along at least a portion of the length of the circuit board 212. Adjacent heating elements 214 are preferably separated from each other along the circuit board 212 length at equal intervals as depicted. However, in some embodiments, irregular spacing between adjacent heating elements 214 could alternatively be provided. Heating element 214 and temperature sensor 216a, 216b placement can be optimized to different trees based on species and age of the tree. For instance, some species of trees move the majority of their sap through the outermost centimeter of wood, whereas other species use much more of their wood for transport. In the former case, it would be advantageous to have a higher density of temperature sensors 216a, 216b in the outermost section of the sap flow sensor 200. By using many temperature sensors 216a, 216b and heating elements 214 controlled individually, the microcontroller 310 can learn where the most active depths are, and focus measurements on that section. Pulsing heat just from certain depths (and not along the entire length of the circuit board 212) allows the measurement of the propagation of heat into and out of the center of the tree. This is another quantity of interest to scientists, and one that is infrequently made. In an alternative embodiment of the invention, one or more elongate heating elements could be provided to run along a length of the circuit board 212 rather than utilizing a plurality of small individual heating elements 214 as depicted in FIG. 2.

In an exemplary embodiment, as shown in FIG. 2, the heating elements 214 extend from the distal end 220 of the circuit board 212 (with the first heating element being spaced a short distance from the very edge of the distal end 220, e.g., in this embodiment with the center of the distal most heating element 214 being spaced about 1-3 mm from the very edge of the distal end 220) towards the proximal end 218 of the circuit board 212. In use, a portion of the proximal end 218 of the circuit board 212 extends outside of the tree trunk and, thus, heating elements 214 are not provided at least on that portion of the circuit board. In addition, sap flow is typically measured at certain depths within the tree trunk. As such, the heating elements 214 may extend only up to that depth along the circuit board. For example, looking at FIG. 2, if the 0 mm point in the circuit board is the point at which the circuit board 212 enters the tree trunk, then the first heating element 214 may, for example, be positioned at a depth of about 5 mm inside of the tree trunk (measured radially). The additional heating elements 214 are then spaced apart from each other at even intervals, for example, about 5 mm intervals as shown in the FIG. 2 embodiment. As further shown in FIG. 2, a plurality of downstream temperature sensors 216a are disposed longitudinally along at least a portion of the length of the circuit board 212 and parallel to the plurality of heating elements 214. A plurality of upstream temperature sensors 2l6b are also disposed longitudinally along at least a portion of the length of the circuit board 212 and parallel to the one or more heating elements 214. The plurality of downstream temperature sensors 216a and upstream temperature sensors 216b are provided on opposing sides of the plurality of heating elements 214 so as to sandwich the heating elements 214 therebetween. Similar to the heating elements 214, adjacent downstream temperature sensors 216a are preferably separated from each other along the circuit board 212 length at equal intervals as depicted. Further, adjacent upstream temperature sensors 216b are preferably separated from each other along the circuit board 212 length at equal intervals as depicted. However, in some embodiments, irregular spacing between adjacent downstream temperature sensors 216a and/or upstream temperature sensors 216b could alternatively be provided. Determining the desired distances between temperature sensors 216a, 216b is the same process as discussed with the heating elements 214. More densely placed temperature sensors 2l6a, 2l6b would be beneficial in sections of the tree with greater variations in sap flow. Larger temperature sensors 216a, 216b could be used if an average measurement of a larger area is desired.

In an exemplary embodiment, as shown in FIG. 2, the downstream temperature sensors 2l6a mirror the positioning of the upstream temperature sensors 2l6b (i.e. are in line with). Similar to the heating elements 214, the downstream and upstream temperature sensors 216a,

216b extend from the distal end 220 of the circuit board 212 (with the first downstream and upstream temperature sensors being spaced a short distance from the very edge of the distal end 220, e.g., in this embodiment with the center of the distal most temperature sensors 216a, 216b being spaced about 1-3 mm from the very edge of the distal end 220) towards the proximal end 218 of the circuit board 12. In use, a portion of the proximal end 218 of the circuit board 12 extends outside of the tree trunk and, thus, temperature sensors 216a, 216b are not provided at least on that portion of the circuit board. In addition, sap flow is typically measured at certain depths within the tree trunk. As such, the temperature sensors 216a, 216b may extend only up to that depth along the circuit board. The PCB 212 may include a printed scale indicating a reference 0 mm mark to measure the relative depth the PCB 212 has been inserted into the tree. For example, looking at FIG. 2, if the 0 mm point in the circuit board is the point at which the circuit board 12 enters the tree trunk, then the first temperature sensors 216a, 216b may, for example, be positioned at a depth of about 10 mm inside of the tree trunk (measured radially). The additional temperature sensors 216a, 216b are then spaced apart from each other at even intervals, for example, about 10 mm intervals as shown in the FIG. 2 embodiment.

As depicted in the FIG. 2 embodiment, the downstream temperature sensors 216a are spaced apart from the heating elements 214 at twice the distance as the spacing between the upstream temperature sensors 2l6b and the heating elements 214. In such embodiments, this allows the temperature of the upstream temperature sensor 216b to rise more quickly due to the conduction of heat through the xylem, while the downstream temperature sensor 216a takes longer to heat due to the convection of heat through the moving sap stream. The exact vertical spacing of the temperature sensors 216a, 216b determines the range of sensitivity. Spacing the upstream temperature sensors 2 lb and downstream temperature sensors 216a closer together makes the measurement of very low sap flow rates possible, however spacing the upstream temperature sensors 2 lb and downstream temperature sensors 216a farther apart allows for the measurement of much faster rates. Depending on the tree age and species, this vertical spacing can be optimized, and additional rows of temperature sensors 216a, 216b may be added to expand the range of sensible flow rates.

As depicted in FIG. 2, the temperature sensors 216a, 216b are in alignment with alternating heating elements 214. Here, the temperature sensors 2l6a, 2l6b are positioned at lOmm, 20mm, 30mm, 40mm, 50mm, and 60mm, while the heating elements are positioned at 5mm, lOmm, l5mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, 55mm and 60mm. Other possible arrangements are possible, however, with temperature sensors 216a, 216b being positioned in alignment with each heating element 214, being positioned in alignment with each third heating element 214, etc. However, in each case, the temperature sensors 2l6a, 2l6b are positioned such that they always line up with a heating element 214 (on opposing sides of the heating element 214) such that after a heat pulse is released from a heating element 214, the temperature of the upstream temperature sensor 216b quickly rises due to the conduction of heat through the xylem, while the downstream temperature sensor 216a takes longer to heat due to the convection of heat through the moving sap stream. Then, according to conventional heat pulse techniques, the time delay required for an equal temperature rise at both temperature sensors 216a, 216b is the time required for convection to move the peak of the heat pulse to the mid- point between the two probes. The heat pulse velocity can then be calculated based on a velocity = distance/time function as is commonly used in the art.

It is to be understood that the spacing arrangements described above in connection with the heating elements 214 and the downstream and upstream temperature sensors 2l6a, 2l6b is only exemplary, and could vary depending upon various factors such as, for example, the diameter of the tree trunk where the device is inserted, the estimated locations of sap flow, etc. Such variables could be determined by one skilled in the art. FIG. 4A shows an exemplary embodiment of the size of a slot 400 created for insertion of the sap flow sensor 10. FIG. 4B shows the placement of the circuit board 12, temperature sensors 2l6a, 2l6b and a heating element 214. Also shown in this embodiment is the placement of a pressure sensor 224 on the PCB 212.. After the slot 400 is created, the tree will slowly exert pressure to close the slot 400. Data from the pressure sensor 224, which is logged by the microcontroller 310, will show how the wound in the tree changes over time. The wound will close around the sap flow sensor 200, increasing the pressure, but the pressure will eventually reach a steady state (e.g., as depicted in FIG. 4C). It is known that sap flow measurements taken before this equilibrium point is reached may be less accurate. Thus, it is important to know when this state is reached. Daily trends in the internal pressure of the tree can also be monitored, which could prove to be another useful diagnostic for tree productivity.

The present system for executing the functionality of the microcontroller 310 described above may be a computer, an example of which is shown in the schematic diagram of FIG. 5.

The system 500 contains a processor 502, a storage device 504, a memory 506 having software 508 stored therein that defines the abovementioned functionality, input and output (I/O) devices 510 (or peripherals), and a local bus, or local interface 512 allowing for communication within the system 500. The local interface 512 can be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The local interface 512 may have additional elements, which are omitted for simplicity, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface 512 may include address, control, and/or data connections to enable appropriate communications among the aforementioned components. The processor 502 is a hardware device for executing software, particularly that stored in the memory 506. The processor 502 can be any custom made or commercially available single core or multi-core processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the present system 500, a semiconductor based

microprocessor (in the form of a microchip or chip set), a macroprocessor, or generally any device for executing software instructions.

The memory 506 can include any one or combination of volatile memory elements ( e.g ., random access memory (RAM, such as DRAM, SRAM, SDRAM, etc.)) and nonvolatile memory elements (e.g., ROM, hard drive, tape, CDROM, etc.). Moreover, the memory 506 may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory 506 can have a distributed architecture, where various components are situated remotely from one another, but can be accessed by the processor 502.

The software 508 defines functionality performed by the system 500, in accordance with the present invention. The software 508 in the memory 506 may include one or more separate programs, each of which contains an ordered listing of executable instructions for implementing logical functions of the system 500, as described below. The memory 506 may contain an operating system (O/S) 520. The operating system essentially controls the execution of programs within the system 500 and provides scheduling, input-output control, file and data management, memory management, and communication control and related services.

The I/O devices 510 may include input devices, for example but not limited to, a keyboard, mouse, scanner, microphone, etc. Furthermore, the I/O devices 510 may also include output devices, for example but not limited to, a printer, display, etc. Finally, the I/O devices 510 may further include devices that communicate via both inputs and outputs, for instance but not limited to, a modulator/demodulator (modem; for accessing another device, system, or network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, or other device.

When the system 500 is in operation, the processor 502 is configured to execute the software 508 stored within the memory 506, to communicate data to and from the memory 506, and to generally control operations of the system 500 pursuant to the software 508, as explained above.

When the functionality of the system 500 is in operation, the processor 502 is configured to execute the software 508 stored within the memory 506, to communicate data to and from the memory 506, and to generally control operations of the system 500 pursuant to the software 508. The operating system 520 is read by the processor 502, perhaps buffered within the processor 502, and then executed.

When the system 500 is implemented in software 508, it should be noted that instructions for implementing the system 500 can be stored on any computer-readable medium for use by or in connection with any computer-related device, system, or method. Such a computer-readable medium may, in some embodiments, correspond to either or both the memory 506 or the storage device 504. In the context of this document, a computer-readable medium is an electronic, magnetic, optical, or other physical device or means that can contain or store a computer program for use by or in connection with a computer-related device, system, or method.

Instructions for implementing the system can be embodied in any computer-readable medium for use by or in connection with the processor or other such instruction execution system, apparatus, or device. Although the processor 502 has been mentioned by way of example, such instruction execution system, apparatus, or device may, in some embodiments, be any computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a“computer-readable medium” can be any means that can store, communicate, propagate, or transport the program for use by or in connection with the processor or other such instruction execution system, apparatus, or device.

Such a computer-readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a nonexhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a random access memory (RAM) (electronic), a read-only memory (ROM) (electronic), an erasable programmable read-only memory (EPROM, EEPROM, or Flash memory) (electronic), an optical fiber (optical), and a portable compact disc read-only memory (CDROM) (optical). Note that the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.

In an alternative embodiment, where the system 500 is implemented in hardware, the system 500 can be implemented with any or a combination of the following technologies, which are each well known in the art: a discreet logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field

programmable gate array (FPGA), etc. The present sap flow sensor 200 utilizes conventional principles with respect to measuring and calculating sap flow through heat pulses and temperature increases, but overcomes the accuracy issues associated with unavoidable misalignment of probes. In addition, the present sap flow sensor 200 removes spacing issues that arise from building probes by hand and installing each probe one-by-one into a tree by providing a single piece design that can be precisely calibrated in a laboratory environment before reaching the field. In addition, wiring the present system is simplified through the use of a connector that plugs directly into a custom microcontroller attached to the device that logs the sensor data and controls the heating elements.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.

Claims

CLAIMS What is claimed is:

1. A sap flow measurement device comprising:

an elongate circuit board having a proximal end and a distal end;

one or more downstream temperature sensors disposed along a length of the circuit board;

one or more upstream temperature sensors disposed along the length of the circuit board parallel to the one or more downstream temperature sensors; and

one or more heating elements disposed along the length of the circuit board parallel to and in between the downstream and upstream temperature sensors.

2. The sap flow measurement device of claim 1, further comprising microcontroller removably attached to the proximal end of the circuit board and configured for logging data from the one or more upstream and downstream temperature sensors and controlling the heating elements.

3. The sap flow measurement device of claim 1, wherein a plurality of heating elements are disposed along a length of the circuit board, and wherein adjacent heating elements are spaced apart at intervals along the circuit board.

4. The sap flow measurement device of claim 1, wherein a plurality of downstream temperature sensors and a plurality of upstream temperature sensors are disposed along a length of the circuit board, wherein adjacent downstream temperature sensors are spaced apart at a first interval along the circuit board, and wherein adjacent upstream temperature sensors are spaced apart at the first interval along the circuit board.

5. The sap flow measurement device of claim 4, wherein each of the one or more heating elements are disposed in alignment with downstream and upstream temperature sensors.

6. The sap flow measurement device of claim 5, wherein the downstream and upstream temperature sensors are in alignment with alternating heating elements.

7. The sap flow measurement device of claim 1, wherein the downstream temperature sensors are spaced apart from the heating elements at approximately the same distance as the spacing between the upstream temperature sensors and the heating elements

8. The sap flow measurement device of claim 1, wherein the upstream temperature sensors are disposed closer to the heating elements than the downstream temperature sensors are disposed from the heating elements.

9. The sap flow measurement device of claim 1, further comprising a pressure sensor disposed along the length of the circuit board.

10. The sap flow measurement device of claim 9, wherein the pressure sensor is disposed on an opposite side of the circuit board from the heating elements and the temperature sensors.