A New Method
Recently a?ÿnew method?ÿhas been developed that enables one to collect redundant invert data at any angle by using a lightweight calibrated measurement rod. The vert rod is a four-sided calibrated measurement rod with each side of the rod calibrated to common recessed angles. When the rod is aligned to the angle of a particular side, the vertical distance is achieved rather than the slope distance.
Introducing the 15ft Vert Rod by Accurate Inverts
The 15 ft Vert rod by?ÿAccurate Inverts?ÿis calibrated to the cosine of each sides corresponding angle, ranging from 0-30o?ÿ.?ÿ?ÿThe rod also includes a digital angle finder which allows field crews to use any angle and quickly achieve a redundancy of measurement. And for added ease, we also included an attached slide marker to help visually confirm pipe sizes.
Redundancy can be achieved by measuring with the multiple calibrated angle sides or by using the 0 side to measure the slope distance and the angle. By noting the slope distance on a random angle, the vertical distance can be calculated later as an office check.
If one aligned the angle finder on the 0 side to 30o, read a slope distance of 11.55 and multiplied by the Cosine of 30o?ÿthe vertical measurement is 10.002 which is exactly the same measurement you would achieve with the rods calibrated 30o?ÿside.
Each side is calibrated this way, but the 0 side also allows one to measure custom angles. This new methodology allows field crews to quickly and accurately collect invert measurements without the need to second guess measurements while also allowing redundant office checks to verify accuracy.
Not bad! Please correct any part of my understanding on how this rod works. The rod is calibrated to the cosine of either the ten or thirty degree rod bubbles. The rod reading is calculated, by the digital level, for any angle other than ten or thirty degrees. You can check the calibration of the digital level by comparing it to the rod reading at ten or thirty degrees.
@field-dog you are correct, the 10, 20 and 30 sides are calibrated to the cosine of that angle, when the level bubble of that side is level the measurement read is the vertical distance instead of the slope. If you level and read each side you will get the same measurement. The 0 side with the digital level allows you to calculate custom angles or check your work. Its rather easy to use, simply extend, level and read your measurement.
Shame on me for missing the twenty degree bubble! All you need to do now is to offer a perpendicular extension to measure pipe inverts in structures with eccentric cones.
You talk about accuracy...have you performed studies at different depths and structures and compared results from different methods (including the product you describe)?
My question is what is the expected accuracy and how did you come to that conclusion?
One problem with this sort of product is that if I were to incorporate it into my workflow, I would need to purchase it, then spend time determining whether it was indeed accurate and usable. The initial cost of the item is the least of the risk as far as money goes. My loss of billable time far exceeds the cost of the product.
If you published some studies of yourself and perhaps others, that might be useful in marketing.
In that discussion...if you had one side of the rod with a scale on it that correctly measured the depth from a 2' offset to the IE, that would be very useful.
Since 99% of the Sewer MH we measure have 48" structures, and a MH lid of 24", if I shoot the center of the lid, then I can measure down from that point. Generally, I reduce the triangle using the observed distance as the hypotenuse. If I had a way to come off a known 2' triangle leg, and then the scale was such that at any given hypotenuse it read the vertical...that would save me time...and it might be faster than trying to figure out which angle works in that particular hole.
@dmyhill technically the rod is calibrated to the trigonometric principle, so its mathematical accurate. The only error that would occur would be due to opperator error, not leveling the bubble correctly, misreading the measurement or flexing the aluminum rod. But we will run some test to see the average error of operators,though our daily use tests have shown it to be quite accurate
average error
Wouldn't that be the standard error? In practice, how often would the rod placement on a pipe invert be exactly 10, 20, or 30 degrees? I think the 0 side would be the one used most often. I'm sure the rod would be quite accurate if used properly. You're dealing with performing 3 things simultaneously though, just like I do when I measure some lake elevations with a mason's line, a line level, and a folding ruler. I like the slide marker; it'll be good for a straight pipe, but a pipe with a bell housing will be a different story.
Can you make these longer?
I've dipped a 25' invert with a 30' rod and the flex was well not helping the accuracy for sure.
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@jitterboogie we are currently developing a longer rod and we are aware of the flex issue with standard rods so we manufacture our rods with aircraft grade aluminum instead of fiberglass to negate this issue as much as physicaly possible.
That's a deep one! I've never heard of a 30' rod before. You probably meant 30' of rod, right?
@field-dog when a manhole or structure is open and the rod is placed on the pipe there is generally a fair amount of free space to move the rod from 10 to 20 or 30 degrees. Often times when we use this in the field we will level at 10 read the measurement then lean the rod to 20 to verify the same measurement, for additional redundancy we may pick a random angel with the digital level then use the measurement to calculate the invert, this will give you the same measurement 3 times.
It sounds cool as hell.?ÿ Can't be any worse than anyone else's ideas and guesses.
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I am sure your product is very precise. I do not intend to question that at all. My question is the accuracy found in practice. I see you have some links on your OP, but I cannot access them for some reason.
So, I would be less interested in the precision of the rod (which I am sure is adequate) than in the resulting accuracy in the field vs best practices.
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Currently, the gold standards would be to enter the manhole and make a series of direct vertical measurements up from the IE to a point on the rim. Of course, no one really wants to enter a condoned space due to the risks and therefore the the safety protocols necessitated.
@dmyhill the resulting accuracy in the field can be verified by the redundant measurements obtained by the rod quite quickly and easily. Measure using the 10 side then flip the rod and verify the measurement on the 20 side, finally you can flip to the 0 side read the digital angle and measurement then use that random angles calc to verify the original 2 measurements. This ability to get multiple redundant measurements is what gives us confidence in the accuracy of the measurement.
If I had a way to come off a known 2' triangle leg, and then the scale was such that at any given hypotenuse it read the vertical...that would save me time...and it might be faster than trying to figure out which angle works in that particular hole.
If you plan to compute the vertical leg using the 24" lid diameter and slope distance you can get?ÿ some error from the fact that the invert is not automatically located directly below the other side of the 24" lid. Most pipes are recessed a few inches from the lid diameter.
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Free idea:
Utilizing the hollow alum rigid rectangular rod,?ÿ
Make a removable plug that allows you to attach two lengths and not lose the imprinted measure lines.
Slip joint with spring loaded clip pins or similar. Good luck love to see what you come up with.
You are correct...but...2.1 or 2.0 at 10 feet is about 0.02' difference...then it is 1.9 on the flip side...so that is 0.04' across the manhole. I actually do use 2.1 or 1.9 or whatever it appears to be. But I can guarantee that if you are repeating to 0.04' on any of these methods, you are doing better work than 99% of the IE measurements out there.?ÿ
The opportunities for errors are many:
You also have a between 0.01' to 0.02 that you have to contend with when measuring a round pipe with a square rod...
You have a bend in the rod...
Rod isn't perfectly plumb...you measure and read from the marked graduation...but the reality is that the edge of the rod is on the ie, since it is tilted, the edge is actually what is touching the IE, so you need to extend the mark across the rod (perpendicular to the rod and not level) to the edge and read it there...
The rod method using a standard level rod is fraught with error. It is nice to see someone trying to make it better.?ÿ
If the advertised rod has a rounded or pointed bottom, it is already more accurate. The sloped graduations for reading the rod also make a huge difference, I would imagine.
I wouldn't mind seeing one in action.
And, one more hope...if a side of that rod can be used as a level rod...BONUS...the real reason that the level rod is used is because it is available.
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@dmyhill really appreciate the input and you are correct, the 0 side of the rod is a standard measuring rod so it could be used for levels, the 10, 20 and 30 sides are calibrated so all you need to do is put it on the edge of the pipe, level and read your measurement. We have been using it for several years and it has greatly simplified inverts for us.