Pyrheliometers (NIP: Normal Incidence Pyrheliometer), are used for measuring direct solar radiation. These sensors are installed on systems rotating with the sun in such a way that the sensor is always normal to the incident radiation. Pyrheliometers only measure the radiation coming from the solar disk, the sensor has an aperture between 5° and 6° unlike pyranometers whose aperture covers the entire celestial vault. The sensitive element is an E6 type thermopile with thermistor, solar radiation passes through a transparent Quartz window only at short wavelengths. Pyrheliometers measure the potential difference (in millivolts) and the resistance of the thermistor (kohms), this resistance allows us to deduce the temperature inside the sensor for a possible correction to be applied. Measurements with filters: For certain applications, radiation sensors can be equipped with filters that allow a certain range of the solar spectrum to pass. The used filters at Tamanrasset are: QUARTZ no colour ( band > = 0.280 μ ) OG530 filter: orange filter (band >= 0.530 μ) RG630 filter: red filter (band >= 0.630 μ) RG695 filter: dark red filter (band >= 0.695 μ) Direct measurements can be carried out in the presence of clouds around the sun provided that the sun is not hidden and the shadow is apparent. These manual observations are taken daily for three times. 09h00,12h00 and 14h00.