ICT International

Advancing soil, plant and environmental decision making

Which Sap Flow Meter Do I Need?

Since 2006, ICT International has undertaken a continuous improvement strategy to produce a comprehensive range of sap flow sensors, meters, instruments, and devices. Using the Heat Ratio Method (for the SFM1 and SFM1x) and Heat Field Deformation (for the HFD Sap Flux Meter), these have taken proven scientific methods to become the leading plant water use measurement solutions.

The Heat Ratio Method is explained in the Sap Flow Measurement article, whilst the Heat Field Deformation method is explained on the HFD Sap Flux Meter page.

Sensor, meter, instrument, or device?

At the core of the sap flow measurement solutions is the definition of whether it is a sensor, meter, instrument, or device.

  • Sensor: converts a physical property into an electrical signal that can be directly related (using first principles) to a biophysical activity.
  • Meter: the reading of the sensor output, and subsequent conversion into a meaningful output for later analysis. Able to perform calculations from the raw measurements for subsequent analysis of derived values.
  • Instrument: a combination of the sensor and meter, often with internal data storage. Contains power (battery) and power supply control (charging circuit).
  • Device: an instrument with internet connectivity (either through LoRaWAN or Cellular) that can transmit the collected data to a cloud-based platform (such as the Eratos SFM Water Usage Workflow, Eagle.io, or Whysor). Importantly, the ICT International range of IoT Devices are platform agnostic, so can be integrated into any existing platform solutions, for example Microsoft Azure as is often used by local government, or a self-managed server solution.

Importantly, a sensor will always require connection to a meter or a data logger to allow collection of the data.

DIfferences between models

Since 2006, ICT International Sap Flow Meters have been installed globally by research scientists (used in over 400 publications), commercial irrigation and rehabilitation management, and for species selection strategies. Each sap flow model has been designed for specific use cases.

  SFM1 Sap Flow Meter SFM1x-UB Sap Flow Meter SFM1x-L Sap Flow Meter SFM1x-C Sap Flow Meter HFD Sap Flux Meter
Sensor, Meter, Instrument, or Device Instrument Instrument Device Device Instrument
Measurement Method Heat Ratio Method Heat Ratio Method Heat Ratio Method Heat Ratio Method Heat Field Deformation
Source Paper Burgess SSO, Adams M, Turner NC et al (2001) Burgess SSO, Adams M, Turner NC et al (2001) Burgess SSO, Adams M, Turner NC et al (2001) Burgess SSO, Adams M, Turner NC et al (2001) Nadezhdina et al. 1998, Nadezhdina and Čermák 2000a, Čermák et al. 2004
Sap Flow Direction Low flow, high flow, and reverse flow Low flow, high flow, and reverse flow Low flow, high flow, and reverse flow Low flow, high flow, and reverse flow Low flow, high flow, reverse flow, and radial flow
Measurement range -70 to +70 cm hr-1 -70 to +70 cm hr-1 -70 to +70 cm hr-1 -70 to +70 cm hr-1
Number of measurement points 2 2 2 2 8, with 2 mm intervals (HFD8-50) and 10 mm intervals (HFD8-100)
Requires external data logger? No No No No No
Communication None Long Range Bluetooth LoRaWAN Cellular None
Internal Storage SD Card SD Card SD Card SD Card SD Card
Access to internal storage USB Cable (micro) Bluetooth or USB C Cable Bluetooth or USB C Cable Bluetooth or USB C Cable USB Cable (micro)
Real-time clock Yes Yes Yes Yes Yes
Compatible with other IoT systems No No Yes Yes No
External Power Supply 20 V DC from either power supply or solar (inbuilt MPPT solar regulator) 20 V DC from either power supply or solar (inbuilt MPPT solar regulator) 20 V DC from either power supply or solar (inbuilt MPPT solar regulator) 20 V DC from either power supply or solar (inbuilt MPPT solar regulator) 20 V DC from either power supply or solar (inbuilt MPPT solar regulator)
Battery Life Expectancy 5 years + if maintained correctly 5 years +, with a user replaceable 18650 Li-Ion 5 years +, with a user replaceable 18650 Li-Ion 5 years +, with a user replaceable 18650 Li-Ion 5 years + if maintained correctly
Applications Laboratory, long term logging for research purposes

Sites with no communication options

Regular monitoring for sites with limited internet connectivity.

Multiple trees or plants in a laboratory setting

Real-time wide area monitoring systems, such as urban or whole plantation.

Integrated with multiple other devices for Soil, Plant, Atmosphere Continuum monitoring

Real-time wide area monitoring systems, such as urban or whole plantation.

Integrated with multiple other devices for Soil, Plant, Atmosphere Continuum monitoring

Laboratory, long term logging for research purposes

Analysis of xylem flux within the tree or plant when in stress conditions. Understanding how xylem flows within the tree or plant, prior to installation of sap flow meters.