Ultrasonic Level Transmitter for Tunnel, Inside Hollow Pipe

"may or may not work" - I concur.

Ultrasonic (or radar) will pulse or shoot down a hollow pipe (sometimes known as a still well or stilling well), but whether the unit interprets the echo properly or successfully it an unknown. It's a "try it and see" situation.

There can be issues like false echo reflections from debris on the inside of the pipe or false echoing off the side of the pipe before a solid bounce can be made from the material itself. Generally, the wider the diameter of the pipe, the higher the chance for success. The smaller the diameter, the more likelihood of failure.

If you're asking whether ultrasonic can be used in a large horizontal pipe, the answer is probably yes, but many ultrasonic transducer do not want to be mounted at the center/top of the dome/curve/arc because it causes problems with echo signal interpretation. I know Siemens recommends moving its transducers to a point 2/3 between the edge of dome top and the center of a dome top tank/vessel.

ultrasonic transceivers come with the different ranges and the conical pattern could be calibrate with the pipe,s internal diameter .as it sense obstruction ,will alarm you .to obtain the pin point results you have to keep the transmitter in exact cent of the tube .for the operational jig ,you can design the motion calculation and the tool and transmitter distance setting .

If the pipe is truly hollow, as in vacuum, no ultrasonic energy will be transmitted through it. If the pipe contains gas or liquid, transmission will be possible.

I would invite multiple ultrasonic vendor representatives to examine your application and bid on supplying the devices with the understanding that they must provide a training and a warranty on the operation of the devices.

Each vendor will know the limitations of their device and if they are required to provide an operational warranty you will be assured of getting devices that will function "as-advertised".

Normally there is not any cost associated with seeking this type of technical support and is part of the sale however in my opinion it would be worth a small investment to ensure the equipment selected functions correctly and reliably .