Abstract: Apparatus for gauging physical dimensions of solid or tubular bodies. Apparatus comprises a capacitive transducer having electrodes forming diametrically arranged pairs of capacitors and means for connecting the pairs, preferably sequentially, in an arm of a four arm electrical network. For circumferential scanning of a solid body along its length, the body is moved along a path of travel through a head assembly including the transducer with the axis of the body being coincident with the axis of the transducer. As the body moves through the transducer the diametrically arranged pairs of capacitors scan the surface to result in a surface profile of the body. For scanning the bore of a pipe or tube the transducer is inserted as a probe and moved along the bore of the pipe or tube, means being provided for maintaining the probe coaxial with the pipe or tube.

Abstract: The size and shape of a body is determined by rolling it between the plates of capacitors, the dielectric constant of which is thereby changed. A capacitor scans sections of the body along its longitudinal axis to detect its diameter and surface faults, a second determines the body's length and a third determines the position of the body. The changes in dielectric constant are compared with those produced by a body of known size and shape so that the size and shape of the body can be determined.

Abstract: Measuring apparatus for determining a linear quantity comprising a capacitance transducer having at least one capacitance variable in accordance with changes in the dimensions of the quantity being measured, and a reference capacitor of substantially constant capacitance with respect to these changes. The transducer and the reference capacitor are connected to two charge amplifiers in two separate arms of a four arm bridge network, the input impedances of the charge amplifiers forming the other two arms. A source is provided for applying an alternating current input signal to the transducer and reference capacitor, and a differential amplifier is provided to receive the output from the charge amplifiers to provide an output related to the value of the linear quantity. The value of the linear quantity may be expressed as the voltage to be applied to the transducer to maintain the variable capacitor at a constant charge.