Abstract: A method of inspecting an abnormality occurring inside a pipe to be inspected, and an apparatus for practicing the method, which includes the steps of transmitting an electric radio or radio frequency (RF) wave having a predetermined frequency from an antenna of a transmitter located at a predetermined position inside the pipe, receiving the transmitted RF wave by an antenna of a receiver located at a predetermined position inside the pipe, and discriminating a characteristic of the received RF wave. The characteristic of the received RF wave can be the intensity of the RF wave, and an attenuation amount is detected in a first example. Alternatively, the characteristic of the received RF wave may be the time required to reflect the transmitted RF wave and receive it with the receiver, and the time interval between transmission of the RF wave and reception of the reflected RF wave is measured in this alternative.

Abstract: A method of measuring the inner diameter of a pipe includes the steps of continuously transmitting RF waves of a predetermined frequency band from an antenna of a transmitter located inside of the pipe to be inspected, receiving the RF waves with an antenna of a receiver located inside the pipe, the antenna of the receiver being spaced apart from the antenna of the transmitter by a predetermined distance, detecting a frequency at a change point where an intensity of the received RF wave changes greatly, and substituting the frequency at the change point into a formula: d=c/1.706f (wherein d is the inner diameter of the pipe, c is the velocity of light, and f is the frequency at the change point) which shows the relation between the inner diameter of the pipe and the frequency to obtain a minimum inner diameter of the pipe.