This device can measure by sensing the temperature difference resulting between the sides of flat, thermally conductive surface when heat flow (heat energy) passes through it.

As shown in the figure, a thin plate with a thermal conductivity of λ(W/mK or kcal/mh°C) and a thickness of d (m) is placed in contact with a heat radiating surface, a heat flow (W/m², kcal/m²h) which goes through the thin plate after it reaches equilibrium can be found by the following method:

Q＝（λ/d）・⊿T

Where ΔT = Temperature difference between two sides of the thin plate, and λ and d are known values, Q can be found by measuring ΔT

The heat flow sensor is made of a thin material with a low thermal conductivity, and its differential thermocouple has multiple contacts to improve its overall sensitivity.

The speed of heat flow (W/m2) can be found from the accurate occurring heat amount and radiation surface area, which are found from the voltage and current given by the main heater.

To prevent the invasion or loss of heat from sources other than the radiating surface, complete insulation is realized by monitoring the heat flow and heating with a backup heater, thereby guaranteeing the radiation surface.

As previously stated, calibration is performed by the standard heat flow device, finding sensor constant α.

Actually, the sensor constant has the heat flow proportion value A and shift value B, and further, value B is a function of temperature.

At KEM, we attach the A constant and B constant values for each sensor with a managed standard heat flow occurrence device installed in a constant-temperature room.

Heat flow value can be obtained by simply touching the heat flow meter sensor to the substance being tested. However, to obtain a more reliable value, there are several points when operating:

The following may lead to error:

1) sensor attachment
2) wind
3) radiation rate
4) heat conduction λ of the substance being measured
5) heat conduction λ of the backfill in embedded sensors

Affixed-type sensors are applied to avoid any air pockets between subject material and sensor. Please use adhesive sheets “HA2-H” or “HA2-L” in affixing the sensors.

It is well-known that heat flow can change due to wind, but trouble also occurs due to change in film resistance.

Because the sensor reads oversensitively to extreme changes, it shows fluctuations larger than the actual heat flow change.

Therefore, the average capability is attached to the device. Also, with a steady wind (or average wind speed), the device will display a value that differs with the actual heat flow.

This is a result of the difference between the transfer constant of what is being measured and that of the sensor.

Generally, the indication is larger because the sensor transfer constant is greater.