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"The?ÿWild N3?ÿhas an important advantage over automatic levels with its stability, making it the instrument of choice in environments where there may be vibrations."
Above is a typical comment, and I understand the design differences between an auto level and a tilting level - and I understand how an auto level with compensator would fail in vibrating conditions, but wouldn't any level fail? Surely the coincidence bubble arrangement would be just as affected? Is the line of sight somehow rendered stable by virtue of the design?
I've never had chance to try one.
Thanks
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Automatic levels use a pendulum that can start oscillating under vibrations.
Automatic levels use a pendulum that can start oscillating under vibrations.
Understood - It just seems like the same conditions that would cause that, would throw any other delicately leveled instrument out of whack also.?ÿ
I haven't used a tilting level, so am only guessing.?ÿ I?ÿ may be wrong, but my guess is that it isn't a matter of going out of whack?ÿ (adjustment problem).?ÿ Rather, I think the slow response of the damped pendulum would make it hard to tell when it is pointing at the right place on the rod.?ÿ The tilting level would have a jittery image but it would be moving quickly around the right spot and the eye could take a better average.
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The pendulum mounted prism in an automatic level actually changes the line of sight to compensate for any un-levelness of the instrument.?ÿ If the pendulum starts oscillating due to vibrations, your line of sight will be all over the place.?ÿ A tilting level might eventually get vibrated out of level, but your sight line won't be dancing like a drunken sailor.
An example - on the 9th storey of a steel fame building the movement of the building seemed to find the right frequency to set up an oscillation in the pendulum. A theodolite (or tilting level) will just move and tilt with the building so your measurements within the building are all actually fine, relatively! I've heard of the switching off the compensator in a total station for this reason as well.
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We have an old N3 for just those sort of conditions. When there is vibration it is certainly slow to set up, BUT...
a physical bubble has a very slow reaction time, unlike the auto-compensator, so effectively it damps out the vibrations. In bad conditions I find it best to "creep" the bubble along a touch at a time and it eventually arrives at a level spot where it wavers slowly about the centre. On this instrument the bubble will continue to creep for several seconds after the touch has been made. Of course, you do need to adjust the bubble for each sight, so it is wise to get it as carefully set as possible on the initial setting up.
However, it will read in conditions where an automatic has no chance at all.
Our oldest T2 theodolite is also a manual one, for the same reason. Once set up we have locks to cover the vertical adjustment screw and it then measures everything relative to the deck of the ship it is set on. Given that any vessel moored outside a dock will slowly move around this is very useful, even if such jobs are only very occasional.
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Informative replies from everyone - Thanks!
The Wild N2 interests me - not only a tilting level but the telescope can be flipped over, which basically is like a peg test incorporated into every measurement.?ÿ http://www.wild-heerbrugg.com/shop/index.php?cPath=1_3_19_71
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Two N2 survive in the very back of our storeroom, one in working order. They were a very nice instrument for precise work, but slow due to the need to take two readings. In adjustment, the readings would be the same. Out of adjustment you meaned the two values. The practical value was that for each important reading you flipped it and read twice, so you knew at once that it was still in adjustment.
We use titling levels (N3s & Brunson) and theodolites (T2s) for machinery alignment, measuring / leveling to 1 arc-sec. The comments above about the coincidence bubble being slower-responding to vibration are correct. We are often dealing with floor / structural vibration from other machines. Using a heavy metal tripod also helps, as does adding some absorptive mating beneath the tripod legs. But there are situations where the vibration will outstrip the levels' ability to provide a good quality reading / and/or a good visual picture of the target scales.
