The standard stationary sequencer applied for this purpose is composed of V5.1 EURO module, output signals drivers module (user selectable output voltage in the range of 5V up to 15 V) and power supply unit. The equipment is housed in 1/2 19" casing manufactured by Rittal company.

However, in the case of examining the flows in wind tunnels around moving objects there emerges a problem of PIV images acquisition synchronization, not only with the set frequency of generated laser light pulse doublets (usually 10 Hz +/- 3%), but also with momentary position of the examined object. Moreover, the experimental set-up is composed of additional components such as object position detection systems.

Phase 1 - stand-by phase aiming at attainment and maintenance of lasers' readiness condition to perform measurement (stabilization of their temperature).
Phase 2 - measurement proper (PIV frames acquisition) and measurement of object position
Phase 3 - transition to stand-by condition before next measurement.

Phase 2 (measurement proper), differing significantly from phase 1 (stand-by), has to begin immediately after receiving the external start pulse. Because the time of this pulse arrival is unpredictable, the usage of standard sequencer is not possible, as there is no time for its indispensable reprogramming (timing change).

In order to solve this problem, a new stationary double sequencer has been developed, making it possible to change the generated sequence of very short time impulses (within nanoseconds) in response to received external start pulse.

This system relies on application of two standard V5.1 EURO sequencer modules, and the additional newly developed HSD-MUX-V10-PD multiplexer module, switching their outputs. All the modules, together with a special power feeder, have been located in 19" common casing appropriate for development into 19" rack.

Programming of the Sequencer
Both sequencer plug-ins can be programmed by means of the sequencer software over two separate RS-232 serial ports (COM1 and COM2). The standard D-SUB 9 connectors are placed on the back plate of the case. For the next generation of the sequencer plug-ins the USB-2 Ports are already implemented.