Method and apparatus for fast sampling in capacitive position transducers

A method for determining, for a capacitive position transducer, a sampling delay interval after an input signal is input to the capacitive position transducer, the method comprising:

• determining a gap distance between a first member and a second member of the capacitive position transducer;
• determining a separation distance between driver electrodes on one of the first member and the second member;
• determining a desired minimum proportion of a signal contrast of a sampled output signal of the capacitive position transducer relative to a maximum signal contrast of the output signal;
• and
• determining the sample delay interval based on the determined gap distance, the determined separation distance, and the determined desired minimum proportion of the signal contrast for the output signal.

A measurement system, comprising:

• a capacitive position transducer, comprising:
• a first member,
• a second member movable relative to the first member along a measurement axis, and
• a plurality of first electrodes positioned on the first member along the measurement axis, and a plurality of second electrodes positioned on the second member along the measurement axis, the plurality of second electrodes variably capacitively coupled to the plurality of first electrodes as the first member moves relative to the second member based on a position of the first member relative to the second member;
• a signal generator supplying input signals to the capacitive position transducer;
• and
• a signal processor inputting output signals from the capacitive position transducer, the output signals indicative of the position of the first member relative to the second member;
• wherein the signal processor comprises a sampling circuit portion for sampling the output signals within a predetermined sampling time interval after corresponding input signals are supplied to the capacitive position transducer, the predetermined sampling time interval selected so that a signal contrast of the sampled output signals is at least a determined proportion of a maximum signal contrast of the output signals.

A capacitive position transducer, comprising:

• first and second support members, the first and second support members displaceable relative to each other, at least one of the first and second support members displaceable relative to a measurement axis;
• a first set of electrodes positioned on the first support member;
• a second set of electrodes positioned on the second support member, differing portions of the second set of electrodes coupled with the first set of electrodes based on the position of the first supporting member relative to the second support member, the first and second sets of first electrodes forming an operable set of transducer electrodes;
• an electronic circuit connected to at least one of the first and second sets of electrodes, the electronic circuit supplying signals to and receiving signals from at least one of the first and second sets of electrodes to indicate the relative position between the first and second support members as a function of the coupling between the first and second sets of electrodes;
• wherein the electronic circuit includes a contamination resistant signal sampling circuit, the contamination resistant signal sampling circuit sampling the signal received from the at least one of the first and second sets of electrodes within a prescribed time interval after the supplied signal, wherein any signal decay effects in the signal paths of signals transferred between the first and second sets of electrodes leave said relative position indication substantially unaffected.