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Enabling better global research outcomes in soil, plant & environmental monitoring.

HFM1 Heat Flux Meter

The HFM1 Heat Flux Meter is a measurement system for analysis of thermal resistance and thermal transmittance of building elements by in-situ measurement. It can be used for measurements according to ISO 9869 and ASTM C1155 / C1046 standards. For ISO 9869 and ASTM C1155 / C1046 standards, the HFM1 is equipped with two Heat Flux Plates (HFP01) as well as two pairs of matched thermistors for differential temperature measurements (four total thermistors).

Thermistor excitation voltage is measured at every measurement interval for increased accuracy, this voltage reading is used in the thermistor scripts to remove errors introduced from possible voltage fluctuations.


  • meteorology
  • building physics
  • H-value and R-value determination
  • building climate control

The in-situ measurement of thermal resistance, thermal transmittance or U-Values of buildings is often applied in studies of building elements.

The thermal resistance, TR, measurement is based on simultaneous measurement of time averaged heat flux F (using a heat flux sensor) and differential temperature, DeltaT, (two temperature sensors).

TR = DeltaT / F

The ISO and ASTM standards on the subject comment on applicability of the method, on installation and on data analysis.

The HFM1 consists of high accuracy electronics (measurement accuracy up to 1 millivolt) as well as matched thermistor pairs to make a differential temperature measurement with better than 0.5°C accuracy. It also includes HFP01 heat flux plates. HFP01 is the world’s most popular sensor for heat flux measurement through building envelopes.


Heat Flux Meter – for ISO9869 thermal resistivity of building materials. Includes: 2 x HFP01 Heat Flux Plate, 2 x THERM-MICRO-10 Temperature Sensors, 2 x THERM-MICRO-30 Temperature Sensor, 1 x CH24 Power Supply, 1 x HFM1: IP65 rated logger enclosure; stand-alone logging capability to 4GB MicroSD Card; Windows software; IP53 rated breakout board enclosure; user manual.

Instrument Logging

Analogue Channels 6 Single Ended (SE) and 2 Differential (channel 1 of 10 total is 2.5V thermistor excitation measurement)
Resolution 0.00001V—24-Bit
Accuracy 0.001V
Minimum Logging Interval 1 second
Delayed Start Suspend Logging, Customised Intervals
Sampling Frequency 10Hz

Measurement Specifications

Test method ISO 9869 and ASTM C1155 / C1046
Measurement locations 2
Differential temperature (DeltaT) matched pairs calibrated thermistors, Part Number THERM-MICRO
DeltaT accuracy 0.5°C
Heat flux sensor type HFP01
Protection: sensors and logger IP 65
Cable length 30m and 10m (Thermistors), 10m (HFP01)
Storage capacity Micro SD card, expandable up to 16GB, 4GB microSD card included.
> 5 years of data.
Data analysis to be performed by the user according to ISO and ASTM standards


Internal Battery Specifications
960mAh Lithium Polymer, 4.20 Volts fully charged
External Power Requirements
Bus Power 8-30 Volts DC, non-polarised, current draw is 190mA maximum at 17 volts per logger
USB Power 5 Volts DC
Internal Charge Rate
Bus Power 60mA – 200mA Variable internal charge rate, maximum charge rate of 200mA active when the external voltage rises above 16 Volts DC
USB Power 100mA fixed charge rate
Internal Power Management
Fully Charged Battery 4.20 Volts
Low Power Mode 3.60 Volts – Instrument ceases to take measurements
Discharged Battery 2.90 Volts – Instrument automatically switches off at and below this voltage when no external power connected.
Power Supply
CH24 Power Supply is supplied in the HFM1 package.
Battery Life varies
Example A: With a recommended solar panel or CH24 connected, operation can be continuous.
Example B: Power consumption is dependent on number and type of sensors connected, frequency of measurement and measurement duration


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