JJF 1172-2007 specifies the calibration method of vocs (VOC) photoionization detector. The instrument is used for the measurement of the concentration of vocs in the air, which is realized by photoionization technology (PID). The instrument uses a 10.6eV or 11.7eV ultraviolet light source, which can ionize organic substances in the air without affecting the basic components in the air (such as N ², O ², CO ², H ² O, etc.). The measured substance is ionized after being irradiated by ultraviolet light in the ionization chamber. The generated ions and electrons form a weak current under the action of an electric field. The concentration of VOC is determined by measuring the current size. The main components of the instrument include a sampling system, a photoionization part and a display part. The specification ensures the accuracy and conformity of the measurement, and the test result is expressed in the total amount of VOC.