Weston, William, Lalor, Michael J. and Cleaver, J.W. (1972) Pulsatile flow measurement in hydraulic systems using a laser velocimeter. Opto-electronics, 4 (4). pp. 417-427. ISSN 0306-8919

Servo valves find their major application in high performance hydraulic control systems where the accurate control of position, velocity and load is essential. Because of this, it is important to determine the dynamic characteristics of the servo valve (i.e. flow rate as a function of input command signal) more precisely.

Previous techniques for this evaluation depended on monitoring spool position using linear transducers, since flow measurement techniques capable of following fast transients and oscillating (or pulsating) flows were not easily applied. The introduction of the laser Doppler anemometer changes this. Steady state flow measurement, using the dual beam scatter system, is now common but since it needs a spectrum analyser to measure the Doppler frequency it is not suitable for unsteady flow. Since hydraulic systems are relatively particle free, the Doppler signals are received intermittently. Because of this, a signal processing system has been developed which measures the period of one or more oscillations in the frequency burst caused by a scattering particle passing through the control volume.

Using this technique steady and unsteady laminar flow profiles have been measured in order to assess its effectiveness in the performance testing of hydraulic servo systems.

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