Inner-loop valve spool positioning control apparatus

A spool control system for positioning a spool in response to a correction signal, the spool being slidably disposed within a block to direct pneumatic pressure and the correction signal being an electrical signal whose level represents the desired position of the spool, the spool control system comprising

• a spool sensor operative to detect the present position of the spool and generate an electrical inner feedback signal whose level represents the present position of the spool,
• a spool movement controller operative to compare a received correction signal to the inner feedback signal to generate an electrical spool positioning signal,
• a spool positioning controller responsive to the spool positioning signal operative to move the spool within the block a distance represented by the spool positioning signal,
• a periodic power supply coupled to the spool sensor to enable periodic sensing of the present position of the spool, and
• a sample and hold circuit operative to maintain the level of the inner feedback signal between periodic samples.

A valve system comprising:

• a fluid passage;
• a valve positioned in said fluid passage and operative to regulate the flow of fluid through said fluid passage;
• a valve actuator coupled to said valve;
• a spool mechanism coupled to said valve actuator;
• a spool sensor operative to detect the present state of the spool and generate an inner feedback signal representing the present state of the spool;
• a spool movement controller operative to compare a received correction signal to said inner feedback signal to generate a spool positioning signal,
• a spool positioning device responsive to the spool positioning signal and operative to alter a position of the spool in accordance with the spool positioning signal,
• a power supply coupled to the spool sensor and operative to cause said spool sensor to periodically sense the present position of the spool, and
• a sample and hold circuit operative to maintain the level of the inner feedback signal between periodic samples of the present position of the spool.