A hardware windowing circuit for LDA in periodic and aperiodic flows
Abstract
This paper describes a microelectronics circuit for the control of the data acquisition of a DISA 55L90a counter. The circuit achieves a hardware windowing function by controlling the ARM and INHIBIT lines of the counter. Two forms of windowing are possible. In the first the windowing circuit allows the counter to acquire, and transfer to a microcomputer for analysis, all particle signals occurring within a certain time window. In the second the windowing circuit permits the counter to acquire and transfer only the first particle signal to occur after a set point in time. The windowing circuit can be cycled through a sequence of windows of either type by either a free running 1 MHz clock or a phase locked loop (PLL). The output frequency of the clock or the PLL is divided by thumb wheel programmable counters to give a wide range of window repetition frequencies. When driven by the phase locked loop the circuit can be used to strobe periodic flows with the PLL following a peroidic, flow generated signal. Oscillating flows, rotating flows and turbomachinery flows, etc., may be investigated using this circuit to obtain windowed data from the flow cycle. When clock driven the circuit can be used to sample data from aperiodic flows in such a way as to eliminate arrival rate bias.
- Publication:
-
Laser Anemometry: Advances and Application
- Pub Date:
- 1985
- Bibcode:
- 1985laaa.conf..321K
- Keywords:
-
- Circuits;
- Electronic Control;
- Flow Measurement;
- Hardware;
- Laser Doppler Velocimeters;
- Windows;
- Circuit Diagrams;
- Clocks;
- Microelectronics;
- Phase Locked Systems;
- Instrumentation and Photography