I have had a request from a client to measure the inside diameter of a number of sanitary sewer manholes that originally we were just going to locate. Do any of you know of a tool that would make it easy to get a measurement of the diameter without entering the manhole? If someone made a device that was basically an ultrasonic tape measure on a stick, that would work. I am sure someone on the board has done something similar at some point.
Any ideas would be appreciated.
Thanks,
JP
IF you can see it, a reflectorless would be great.
:coffee:
Take two yardsticks and a disposable wino.
Do any of you know of a tool that would make it easy to get a measurement of the diameter without entering the manhole?
If I were you, I wouldn't even consider entering the manhole without proper Confined Space training and certification.
Do as RFB recommends, go reflectorless if possible.
Count the number of bricks around the circle. Do the math. You won't be reporting diameter to the nearest 0.001 feet anyway.
:good:
A folding ruler, duct tape, and a stick, lathe, or range pole long enough to reach past the cone on top. Should get you within a few inches. Measure the radius, not the diameter.
James
Try using an old level rod. I always scribbled an approximate area on the bottom of the rod with keel(crayon), lower the rod into the flowline of the pipe, and twist the rod which makes a mark in the keel. A philadelphia rod works best because it makes an indention in the wood.
I've done this and it works. Where it can be a problem is with eccentric cones, but same concept. You just need to be more creative and have lots of duct tape.
It will get you within "close enough" for nominal diameter dimesions. You will have to learn to live with the fact that you aren't building a watch.
Along the same lines you could affix one of those laser measuring deals and lower it down, as long as you could read it from the top.
Nail a lath across the rim and make a magic marker mark at about center. Then read a level rod reading from bottom of m/h wall to the mark, and then grab a Smart Level (carpenter's level with digital angle) and read the angle of the level rod. Do it for the other side and then figure your triangles.
I used to get decent invert elevs that way.
I am presuming that they are not pre-cast structures...otherwise all you would have to do is call manufacturer...
If you have many to do, you could fabricate a "inside diameter caliper" out of 1/2" plywood. Cut two "L"'s and bolt them together about 1/3 down from the long part. The short section should be long enough to fit into the manholes and the long section should be about 6' long. Bolt together facing opposite directions. Calibrate the top section with a marker by measuring the distance between the ends of the short section at different intervals. Google it and you'll get the idea.
Inside Diameter May Be Useless...
...if the manholes are not concentric. For eccentric manoles at least 4 center to face measurements are necessary and they must be oriented to your survey system.
Paul in PA
