directional and spectral characteristics, a Gardon gauge's main components are: A thermocouple sensor with a black coating. This sensor absorbs all radiation, has a flat spectrum covering the 300 to 50,000 nanometer range, and has a near-perfect cosine response. The black coating on the thermopile sensor absorbs the radiation that is converted to heat. The heat flows through the sensor to the sensor housing and from the housing to the cooling water. The thermopile sensor generates a voltage output signal that is proportional to the heat flux. Usage Gardon gauges are frequently used in fire testing. Typically installed vertically and next to the sample under testing. Gardon- or Schmidt Boelter gauges are unprotected heat flux sensors, and that they are highly sensitive to local convection. In general users should make sure that: Radiation is dominant, which is generally the case above 50 kW per square meter Convection is not carrying away too much of the flux; this may happen at high air speeds or in case the sensor temperature and air temperature are very different (so air temperatures above 500°C Standardisation Gardon gauges are standardised according to the ASTM standard. References Measuring instruments Radiometry