US Patent 7856730 Internal diameter measurement device

The internal diameter measurement device is inserted into a cavity to measure its internal diameter. The internal diameter measurement device includes: a tubular sheath inserted into the cavity; a balloon which is provided on a distal end portion of the sheath, and is capable of expanding by supplying a fluid to an inner portion thereof; a linear reference member having a first end portion fixed to the distending portion or the distal end portion of the insertion portion, and a second end portion moving towards the distal end of the insertion portion in conjunction with the expansion of the distending portion; and a measuring portion which is provided in a proximal end portion of the insertion portion and is capable of confirming the position of the second end portion of the reference member. This internal diameter measurement device enables accurate measurement irrespectively of dimensions of a pipeline to be measured.