| 摘要 |
In one form of the invention, the control apparatus includes two stages: a poppet first stage and a piston second stage. The poppet first stage includes an altitude sensitive evacuated bellows coupled to a poppet valve. The second stage piston includes a pair of opposing head portions separated by a rod portion. The apparatus includes an output port which is coupled to a low pressure pneumatic signal or to a high pressure pneumatic signal, depending upon the position of the piston. For altitudes less than a predetermined altitude, e.g., 20,000 feet, the first stage develops a pneumatic servo signal which causes the piston to be in a first position which couples the output port of the apparatus to ambient air pressure. For altitudes greater than the predetermined altitude, the first stage develops a pneumatic servo signal which causes the piston to be in a second position which couples the output port of the apparatus to a high pressure pneumatic signal. The high pressure pneumatic signal may comprise the compressor discharge pressure of a gas turbine engine. Backup means is provided for accommodating failure of the bellows. Indicator and adjustment means are also provided for ensuring an accurate, reliable, and repeatable, control apparatus output signal.
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