Proximity sensing transducer with simulation means

A transducer for detecting information as to an article in proximity thereof, comprising:

• a field creating coil,
• sensing means comprising a pick-up coil positioned to be within that field and responsive to changes in that field such that when it is disturbed by the proximity of the article, the sensing means operates to provide information as to the article, and wherein said field creating coil includes two parts, one part being wound around an elongate core and the other part being similarly wound on another elongate core, the longitudinal axis of both of said cores being fixed at right angles to one another, and wherein said pick-up coil is wound around a further elongate core, said further core being fixed at right angles to both of the other cores with all core axes intersecting so that the pick-up coil is situated in a field strength minimum created by the interaction of the fields emanating from the parts of the field creating coils, and
• a field disturbing coil having two parts, one part being mounted coaxially with said pick-up coil at a position where the field has minimum strength when an article is not in proximity to the transducer and the other part is at a position other than where the field has minimum strength and wherein said parts of said field disturbing coil are electrically interconnected with a resistance and a switch, so that when the switch is closed the field is redistributed and the voltage induced in the pick-up coil will change thereby simulating the presence of an article, the value of the resistance being chosen such that the voltage induced in the pick-up coil is known and will be different from the voltage induced when an article is in proximity of the transducer so that the voltage induced by the proximity of an article can be distinguished from the voltage induced when the presence of an article is merely simulated.

A method for detecting information as to a simulated article comprising:

• (a) creating first and second fields at respectively first and second positions whereat a simulated article is to be detected;
• (b) providing first and second field sensing means at predetermined spatial positions within the first and second fields respectively, both field sensing means being responsive to changes in the strength of their respective fields at their respective positions;
• (c) creating a known redistribution of each of said fields without substantially changing the power in the field in a manner whereby the redistribution of the field is substantially identical to the redistribution that would be caused by an article in proximity to the field;
• (d) observing the response of each field sensing means to the redistribution of its respective field;
• (e) correlating the nature of the responses of said sensing means to the nature of the input creating the known redistribution of the field, whereby information is detected at respectively each of said first and second positions as the simulated article passes the two positions in proximity to the respective fields;
• and
• (f) using the information from the two positions to ascertain any of the following:
• (1) presence of the simulated article;
• (2) direction of movement of the simulated article, and
• (3) velocity of the simulated article.