Calibration of the CERTIFIER Air Velocity Calibrator Using a Laser Doppler Velocimeter (LDV)

Introduction Traditionally a Pitot-static tube connected to a pressure transducer is used to make air velocity measurement. Lately, velocity transducers based on the principle of convective heat transfer have become popular. Both types of transducers need occasional calibrations. Also, several regulatory agencies require that the calibration of velocity transducers used in certain applications must be verified at regular intervals. While evaluating a velocity transducer calibration facility, one must consider two essential factors. One is the quality of air stream, and the other is the method used to establish the reference velocity in the calibration facility. A suitable calibration facility must provide a test section area large enough to avoid blocking effects, have good motor speed control, and provide an air stream with spatial uniformity and steadiness of flow. A well designed wind tunnel usually meets these requirements at velocities above 750 ft/min (FPM). However, to accomplish similar effects at lower velocities (30 to 750 FPM) is much more difficult.