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AutoCap Gap Measurement System

AutoCap is the most versatile of the Rotadata suite of gas measurement systems utilising both the actuator driven near to approaching electrode and a capacitance electrode both built into the same measurement probe. So the system combines the strengths of the RotaTip and the RotaCap systems well suited to the measurement demands required for military aero-engines.

The AutoCap probe is a coaxial device consisting of a fixed outer casing containing an internal sliding electrode assembly. The internal assembly, consisting of both capacitance and near too touch electrodes, is driven through the outer casing of the engine by an end-mounted actuator until a voltage at on the touch electrode discharges to the longest blade. The assembly then stops and begins to ‘hunt’ backwards and forwards to the ‘touch’ point to ensure the contact position is measured accurately.

At the same time the capacitance electrode gives pulses for each blade on the engine rotor at the ‘touch’ point. The relative amplitude of the pulses, together with the known clearance of the longest blade, is used by the control computer to calculate the clearance of every blade on the rotor. The actuator is attached to the engine outer casing by a mounting tower. Both the ‘touch’ and the ‘capacitance’ probe electrodes are part of the internal (sliding) probe assembly and move together.

To compensate for casing expansion over time and in differing operating conditions, the ‘touch’ probe must be reversed out of the engine periodically to re-establish the datum. All such movements are performed automatically as a function of the AutoCap controlling software. They are invisible to the operator.

All AutoCap operations are controlled from the computer.

The software provided by Rotadata generates five main display windows covering all aspects of the AutoCap configuration, calibration, measurement and results presentation, together with a window for diagnostic procedures. Normally, operation is automatic on clicking screen buttons, but a facility is provided for inserting commands manually during setting up and fault diagnostics.