Guys and Gals,
I have used a PipeMic quite a bit in the past, but today I used it in a different way, and I am puzzled. I am sure it is something simple I am not catching. I'll gladly take the ribbing, but I want to make sure I am not thinking incorrectly.
Today's task was to shoot the elevation of the top of a weir on a sewer effluent tank. The shot cannot be read with a plumb rod because the weir is directly under the edge of a catwalk. My thought was to use the PipeMic as an extension to shoot the top of the weir. I have attached a sketch below.
I am thinking that my rod reading with the PipeMic attached should be a lower number than the reading without the PipeMic attached. Am I overlooking something obvious? The only thing I can think of is the PipeMic we have had for several years has some slack in it, and is not making a 90 degree angle with the level rod.
Thanks in advance
The pipe mic may be getting old, causing the angle of the arm to be more acute. If your difference in deltas is consistent which it appears to be as long as I'm reading your sketch correctly than you should get a good elevation. The only other less likely thing it could be is your rod is somehow seated .11 lower than it should be in the pipe mic
If you're not comfortable with that I would personally do a double check by getting a 3 or 4 foot long regular carpenters level, measure the thickness. Then hold that on the top of the weir with your rod on top. If you're good at multitasking then bend down, make sure you're carpenters level is level, put a frogs eye on your rod and measure. Then just subtract whatever the width of the level is from your elevation. It would be a good sanity check.
Thanks for the reply. We shot the top of the weir with the total station and a prism rod. It isn't a plumb shot, but is it a rough check. I am going to do a quick check tomorrow with the rod and the pipe mic before the guys head out. I can't return to the site, as they had to draw down the tank for us to get a shot on the weir. They cleaned the weir before we shot it.
I ma confident in the readings, as I did a check before I left the site early this morning, and my readings on the benchmark was about the same difference as what the guys reported. It just doesn't seem "normal".