Flare radiation monitor / heat flux sensor

HF02 is a sensor that measures radiant heat flux or thermal radiation in the outdoor environment. A common application is monitoring the radiation emitted by flares. HF02 is certified for use in potentially explosive atmospheres, and is rated for radiation levels up to 15 x 10³ W/m². We recommend use of HF02 in a decision-supporting role only, and not to use measurements of HF02 as the main or sole source of information for judging safety.

  • Robust
  • All-weather
  • Suitable for potentially explosive environments


HF02 is Certified for Use in Potentially Explosive Atmospheres
HF02 is used in alarm systems, using the heat flux measurement to issue a warning in case of high thermal radiation exposure of equipment or personnel. It is typically installed close to a flare. A common assumption is that the heat flux level in a safe environment for personnel must not exceed 5 x 10³ W/m² (or 1.5 x 10³ BTU/(hr∙ft²)). Above that heat flux level, or when the temperature of the sensor body exceeds 70 °C, an alarm is activated. A typical alarm system will include multiple HF01 sensors, all aimed at the main source of radiation, as well as other decision-supporting devices such as camera systems and temperature sensors. The sensor in HF02 measures the heat flux to its black (absorbing) surface, in the plane of the sensor, from a source in the field of view angle. It offers a measurement of the effective exposure for personnel and equipment from a source in the direction it is aimed at the location of the sensor. As the detector is essentially open (it has no protective windows) the measurement is influenced by wind in the same way as any exposed surface such as clothing worn by personnel or the surface of equipment; increased wind speed leads to a reduction of the measured heat flux. Rain on the detector can also lead to cooling and a reduction of the measured heat flux.

Suggested Use

  • Outdoor flare monitoring

Areas of Application

Industrial monitoring and control / heat flux and heat transfer measurement



heat flux sensor temperature

Measurement range

-30 to + 100 °C0 to 15 x 10³ W/m²

Sensitivity (nominal)

0.3 x 10⁻⁶ V/(W/m²)

Model names according to EU type examination

LEX35A, LEX35B or LEX35C

Heat flux sensor


Temperature sensor

thermocouple type KX

EC type examination certificate

included in delivery

ATEX rated operating conditions

II 2 G EEx d IIC T6

Electrical data

U[max] 5 V, I[max] 5 x 10⁻³ A

Rated process temperature range sensor and high temperature cable

-20 to +70 °C

-High temperature cable

3 m (see options)

-Sensor and high temperature cable


-Low temperature extension cable


Safety notes

see manual

Maintenance requirements

see manual


• Longer cable: standard length of the high temperature metal sheathed cable as well as the low temperature extension cable is 3 m. Both can be extended up to 100 m
• Sensitivity: we offer dedicated converters for HF02 to provide a standardised output
• Shielding options: the standard version has the sensor body and the high temperature cable connected to the shield/drain wire of the low temperature plastic cable. A shield disconnected from the high temperature metal cable and sensor body is offered as an option


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