GG01 is a water-cooled sensor that measures heat flux. The Gardon gauge sensor is based on copper and copper alloys, and works at heat flux levels at which other sensors get toasted. Optionally GG01 can be equipped with a sapphire window; to measure radiative heat flux only, and not convective heat flux. GG01 has an on-board thermocouple type K and is available with various dedicated measurement ranges.

  • Withstands very high heat fluxes
  • Fast response time
  • Equipped with type K thermocouple to measure body temperature
  • Suitable for use in high vacuum
  • Safe storage with a practical protection cap



Measurand heat flux
Measurement range (250, 500, 1000) x 10³ W/m²
Measurand in SI units irradiance in W/m²
Sensor technology Gardon
Rated cooling water flow (see manual for more information) > 50 l/h (0.014 l/s)
Nominal response time (63 %) at different rated measurement ranges :
250 x 10³ W/m² 250 x 10⁻³ s
500 x 10³ W/m² 200 x 10⁻³ s
20, 50 x 10³ W/m² 200 x 10⁻³ s
1000 x 10³ W/m² 100 x 10⁻³ s
Limiting measurement range 150 % of rated measurement range
Output signal DC voltage
Output signal range > 5 x 10⁻³ V at rated measurement range
Full field of view angle 180 °
Calibration traceability to ITS-90
Calibration laboratory :
-management system certification ISO 9001
– accreditation not accredited
Calibration method secondary calibration method according to ISO 14934-3
Standard cable length 2 m (see options)
Order code standard version GG01/rated measurement range/cable length
Options Rated measurement range (250, 500, 1000) x 10³ W/m²
Sapphire window (for GG01-250 only)
Longer cable (specify either 5 or 10 m)


GG01 42 webv2001

GG01 measures heat flux in the range of (250 to 1000) x 10³ W/m². Equipped with a black absorber, heat flux sensors of this type are designed for measurement in an environment in which heat flux is dominated by radiation. Using an open detector, GG01 is also sensitive to convective heat flux.

The GG01 Gardon gauge sensor, based on thermocouple materials, generates an output voltage proportional to the incoming irradiance. A type K thermocouple measures the body temperature. The sensor is water-cooled. Water cooling is usually supplied by tap water.

GG01 68 webv2001

There are 3 versions of GG01; each with a different rated measurement range, sensitivity and response time. Irradiance ranges are (250, 500 and 1000) x 10³ W/m², for GG01-250, GG01-500 and GG01-1000 respectively. The body is equipped with a flange for easy mounting. GG01-250 may be equipped with a sapphire window. See options.

GG01 72 webv2001

GG01 is made using oxygen-free high thermal conductivity copper and thin foils of a copper-nickel alloy. The sensor is called “Gardon gauge” after its inventor Robert Gardon. The benefit of this technology is that it can withstand very high heat fluxes.

hfluxman GG01 GGC01 113 webXL squarev2001Hukseflux invested in brand new manufacturing and test equipment for producing modern Gardon gauges. Each sensor is tested at its rated range.

All GG01s are tested to withstand a cooling water operating pressure of 10 bar.

GG01SW 046 webv2001Optionally GG01 may be equipped with a sapphire window (GG01-250-SW). It allows the user to measure only the radiative component of the heat flux.


Suggested Use

  • GG01 is the sensor of choice for high heat flux measurements.

Areas of Application

  • Industrial monitoring and control / heat flux and heat transfer measurement
  • Scientific research / heat and heat transfer measurement

Frequently asked questions

How to measure heat flux?

Heat flux sensors measure energy flux onto or through a surface in [W/m²].
The source of the heat flux may be:

  • conduction
  • radiation
  • convection

Convective and conductive heat transfer are associated with a temperature difference. Heat always flows from a source to a sink, from a hot to a cold environment. Convective and conductive heat flux is measured by letting this heat flow through the sensor. Radiative flux is measured using heat flux sensors with black absorbers. The absorbers converts radiative to conductive energy. Hukseflux started in 1993 with sensors for measurement of heat flux in soils and on walls. In the course of the years, we have added specialised sensors and systems for many other applications.
Heat flux sensors manufactured by Hukseflux are optimised for the demands of different applications:

  • rated temperature range
  • rated heat flux range
  • sensitivity
  • response time
  • chemical resistance, safety requirements
  • size, shape and spectral properties

Hukseflux is the world market leader in heat flux measurement. We have prepared a white paper briefly explaining the fundamentals of measuring with heat flux sensors. It also offers general directions what to watch out for and some, perhaps surprising, applications of heat flux sensors. Take a look at our white papers.

What matters most when measuring with a heat flux sensor?

There are quite a few general considerations when starting a heat flux measurement.

  • Representativeness in time and space; average!
    A heat flux sensor measures at a certain location. Is this location representative of what you need to measure? If possible, use a relatively large sensor, rather than a small one, and consider use of multiple sensors. Thermal processes often have large time constants; instantaneous measurements may be misleading. Average to get the full picture.
  • Optical properties
    When heat flux sensors also measure radiation, pay attention to the surface color. If needed paint the sensor surface. Please mind that shiny metallic surfaces reflect both infra-red and visible radiation. Paints may have different colors in the visible range, but are usually “black” absorbers in the far-infra-red.
  • Sensor thermal resistance
    A heat flux sensor distorts the local heat flux. In order to minimize this effect, use the sensor with the lowest possible thermal resistance.
  • Edge effects
    A heat flux sensor locally distorts the heat flow pattern, in particular around the edges of the sensor. A passive guard, i.e. a non-sensitive part around the sensor is essential to avoid errors due to edge effects.

There are more characteristics that matter. Please find them in our white paper on heat flux fundamentals and applications.

Which sensor(s) to use for surface energy flux measurement?

Hukseflux manufactures a range of sensors for surface energy flux measurements. All have proven reliability.
These state-of-the-art sensors are made for the global fluxnet community:

  • NR01 is a market leading 4-component net radiometer.
  • HFP01 and HFP01SC measure soil heat flux.
  • STP01 offers an accurate temperature profile measurement.
  • TP01 is the leading sensor for soil thermal conductivity.

Sensors made by Hukseflux are designed for compatibility with most common datalogger models. For many models we have example programs and wiring diagrams available.

How to measure R-value and U-value of buildings?

On-site measurements of thermal resistance, R, are often applied in studies of buildings. Alternatives are to measure its inverse value, the thermal conductance which is called the Λ-value, or the thermal transmittance which includes ambient air boundary layer thermal resistance, the U-value. The measurements of R are based on simultaneous time averaged measurement of heat flux Φ and differential temperature, ΔT, (using two temperature sensors on each on a different side of the wall).

R = ΔT / Φ

Hukseflux provides a range of sensors and measuring systems for use in measurement of the energy budget of buildings and characterization of construction materials.

HFP01 heat flux sensor and TRSYS01 measuring system are widely used for on-site measurements on walls, windows and other construction elements in building physics.

  • HFP01 can be used for in-situ measurement of building envelope thermal resistance (R-value) and thermal transmittance (H-value) according to ISO 9869, ASTM C1046 and ASTM 1155 standards. HFP01 is the world’s most popular sensor for heat flux measurement in the soil as well as through walls and building envelopes. HFP01 measures heat flux through the object in which it is incorporated or on which it is mounted, in W/m². More information? Visit the HFP01 product page.
  • TRSYS01 is a high-accuracy system for on-site measurement of thermal resistance, R, thermal conductance, the Λ-value, and thermal transmittance, the U-value, of building envelopes. TRSYS01 is mostly used for measurements according to standard practices of ISO 9869 and ASTM C1155 / C1046. The system is equipped with high-accuracy electronics, two heat flux sensors of model HFP01 as well as two pairs of matched thermocouples. The two measurement locations provide redundancy, leading to a high level of confidence in the measurement result. The high accuracy of the heat flux sensors and temperature difference measurements ensures that TRSYS01 continues measuring when other systems no longer perform; in particular at very low temperature differences across the wall.

Where can I find complete heat flux measuring systems?

Hukseflux, market leader in heat flux measurement, offers both sensors and systems.

These measuring systems typically include a Measurement and Control Unit and one or more sensors for measuring heat flux as well as other measurands, such as temperature and humidity. Examples are the TCOMSYS01 Hot Cube thermal comfort measuring system, including a TCOM01 sensor, and the TRSYS01 measuring system, incorporating two HFP01 heat flux sensors and two pairs of matched thermocouples.

Cannot find what you are looking for? Please contact us.