Electrical length measuring system

Claim 2

Electrical length measuring system comprising a differential capacitor transducer, at least one receiving plate on one side of the capacitor, at least two transmitting plates on the other side of the capacitor, means for moving the sides of capacitor relatively to and in parallel with each other; a control system having an input and an output; a plurality of reference DC voltage sources; switching means for alternately connecting each transmitting plate between the output voltage of the control system and one of the reference DC voltage sources, means for feeding back the alternating voltage picked up by the receiving plate as a result of relative movement between said plates to the input of the control system in such a way that the signal on said at least one receiving plate is driven back to zero whereby to ensure that the output voltage of said control system is in a linear relationship with the relative displacement of the plates of said capacitor.

Claim 3

Electrical length measuring system as defined in claim 1, in which an electronic switch is connected to each transmitting plate, a square wave source and an inverter for driving said electronic switches in such a manner that during one part of the period of the square wave source both transmitting plates are connected to the output voltage of the control system, and during the other part of the period to a respective said reference voltage.

Claim 4

Electrical length measuring system as defined in claim 1 wherein one of said reference voltages is zero.

Claim 5

Electrical length measuring system as defined in claim 2, in which the electronic switches are of the field effect type.

Claim 6

Electrical length measuring system as defined in claim 1, in which a high input impedance pre-amplifier is coupled to said at least one receiving plate.

Claim 7

Electrical length measuring system as defined in claim 1, in which the control system consists of a synchronous demodulator and an integrator connected thereto.

Claim 8

Electrical length measuring system as defined in claim 1, in which the control system consists of two synchronous demodulators and a difference integrator, there being means for driving said demodulators by opposite phases, the output of said demodulators being connected to the inputs of the difference integrator.

Claim 9

Electrical length measuring system as defined in claim 1, in which the control system consists of a comparator, a digital synchronous demodulator connected to the output of said comparator, an up/down counter the mode input of which is connected to the output of the digital synchronous demodulator, and a digital-analog converter connected to receive the output of said counter.

Claim 10

Electrical length measuring system as defined in claim 8, in whIch a further counter has its mode input connected to the output of said digital synchronous demodulator, said further counter being independently settable to zero or a predetermined number, a display/information processing unit being connected to said further counter.

Claim 11

Electrical length measuring system as defined in claim 1, in which a plurality of consecutive plates of equal length forms the transmitting side of the transducer, switch means for connecting said plates in such a way that several consecutive plates belong to a group having the same electrical potential, and means for displacing electrically the group so as to track the displacement to be measured.

Claim 12

Electrical length measuring system as defined in claim 10, in which the receiving side of the transducer is also formed by a plurality of consecutive plates, receiving plates alternating with grounded plates, the distance separating the middle of two consecutive receiving plates being equal to 2N times the distance separating the middle of two consecutive transmitting plates, where N is a positive integer, and in which analog switches connect the transmitting plates to one of two alternating voltages, generated by switching between the output voltage of the control system and one of the said reference voltages, control circuitry for controlling the analog switches in such a way that there are always N adjacent transmitting plates connected to one of said alternating voltages, and the next N adjacent transmitting plates connected to the other, and that by moving the transmitting plates relatively to the receiving plates by the amount of the centre distance between two transmitting plates, the electrical distribution pattern of the transmitting plates will be moved by the same amount.

Claim 13

Electrical length measuring system as defined in claim 11, wherein an up/down Johnson counter and several inverters connected to the output of said Johnson counter constitute said control circuitry so as to insure a correct electrical distribution pattern of the transmitting plates, and means for feeding a logic signal to said Johnson counter in order to alter the distribution pattern of the transmitting plates by a predetermined amount.