Woodward VS-I Remote Servo Only Construction

Rotary Servo Valve

The hydraulic servo valve has five ports: Supply, two Control Ports, Over Board

Drain (OVBD), and Drain/Tank. With the hydraulic valve in its middle position,

both control ports are blocked. As the valve rotates, supply pressure is

connected to a control port while simultaneously connecting the drain to the other

control port. The combined action of the servo position controller and cylinder

position controller modulate the power cylinder position as necessary to match

the input demand. OVBD is permanently connected to drain and can (optionally)

be connected to the OVBD connection on Hydraulic Power Cylinder to drain any

leakage pass the primary rod seal.

A unique function of the software is a periodic, symmetrically opposed impulse

(called "Silt Buster") which flushes silt and debris from the servo valve without

causing undue wear. At the interval and amplitude selected by the user, this

function provides a very rapid motion of the hydraulic valve, allowing any silt to

be flushed to the drain passage. This motion is followed immediately by a step of

equal amplitude in the opposite direction. The opposing symmetry of the impulse

results in no net change in fluid volume to the controlled servo valve, and thus

does not interrupt the control of the turbine. This unique function provides a

higher degree of stability, reliability, and silt resistance.

If the unit detects any diagnostic shut down condition, or if the detected

diagnostic condition prevents reliable control, or if a loss of power occurs, the

servo valve return spring forces the valve to connect the appropriate control

pressure to drain, causing the cylinder to move to the fail-safe position.

Electronic Driver Module (PCB)

The printed circuit board (PCB) is mounted on top of the housing (see Figure

1-6). The PCB performs the following tasks:

 Power Supply

 Isolated Input and Outputs

 Dual Redundant Demand Inputs

 Dual Redundant Inputs for Final Cylinder Feedback

 Microprocessor-based Control

 Actuator H-Bridge Drive

 Current Limiting for Thermal Protection

 Advanced Diagnostics

 Discrete Outputs for Fault, Alarm, and Shutdown Enunciation

The shield connections for the Analog Output (terminal #20), CAN1 (terminal

#23), and CAN2 (terminal #29) are through capacitors only as indicated in the

wiring section of this manual.

The power supply section performs the EMI filtering on the (18 to 32) V (dc) input

voltage and generates controlled voltages for several electronics sub-systems.

The power supply system is monitored for proper operation. If input voltage or

internal power systems are detected outside of allowable operating ranges, a

diagnostic alarm will be enunciated.

Calibration and configuration of alarms and shut down and redundancy operation

are configurable via the PC Service Tool.

The primary demand and redundant demand / feedback input signals are

designed for a (4 to 20) mA control signal. Each input signal is EMC protected.

Discrete outputs are provided for alarm and shut down enunciation. An internal

LED also is illuminated when a fault condition is detected. Cover needs to be

removed to see this LED. The configurable discrete output can be customized to

output a variety of enunciations using the PC Service Tool. All of the discrete

outputs are configurable for normally-open or normally-closed action using the

PC Service Tool.