The unique feature of this camera is the ability to acquire coupled pairs of frames in a very short time interval which can be set down to 500ns. This short time interval is essential for the PIV measurements in the case of the high speed fluid flows. The integration time of the first picture can be set in the range from 1Ás to 100ms. The integration time of the second picture is constant and equals to 90ms. Each acquisition of the pair of frames is initiated by TTL pulse sent to trigger input of the camera. In the response on the trigger pulse the camera starts the exposure process of the first picture with predefined integration time. After predefined integration time, the second picture is exposed. During the second picture integration, the first image is sent to PC. After completion of the second integration, the second image is sent to PC.
The PIV measurements must be performed in a dark room, while the object is illuminated with short laser pulses. The first laser pulse illuminates the object during the first image integration, and the second laser pulse illuminates the object during the second image integration. This principle and conditions of camera function lead to the procedure when the lasers determine images exposure time and time interval between pictures.
The whole PIV set-up consisting of a double-pulse laser and the above mentioned double frame camera system is synchronized by means of the sequencer unit. . It can generate complex patterns of pulses (sequences) on its 16 outputs. Both the pulse width, and the spacing between the pulses can be precisely programmed by user and edited on the friendly graphic interface.
The requirements for camera working in flow measurement system with the application of PIV method cause that sensor works in non-standard conditions. The level of camera noise is a very important parameter. Excessive level of noise decreases the accuracy of calculations related to coupled images correlation.Camera parameters can be significantly improved by application of sensor cooling system. Sensor cooling down to -20C significantly improves the signal to noise ratio and the camera sensitivity.A two-stage cooling system, based on two Peltier elements has been applied in the camera.