Tribrach Adjustment

Video of procedure

should help. I always used the total station or theodolite to check the circular bubble and the simpler adjustment ring shown.

We use an adjustment ring similar to this one:

http://www.loink.com/product/48/surveyingoptribrachadjustingsupplies

Thanks for the replies.

I have the Seco adjusting ring with the spirit level. I seem to be having trouble with the small screws in the optical plummet adjustment.

I think I have it figured out, but was wondering if anyone had an instruction sheet. I found one last night from a calibration class that Hayes put on several years ago.

Thanks,
Jimmy

Is there an advantage in speed or accuracy to using the adjusting fixtures that are sold?

I've used the simple procedure of checking the tribrach bubble against the instrument level in all rotations, and then the "pencil line on tripod" method.
See [msg=113661] https://surveyorconnect.com/index.php?mode=thread&id=113661 [/msg]this thread.
A New Jersey Dept of Transportation document gives it in 5.5.1.3

Start with the tripod head approximately level so not much motion is required on the tribrach screws.
Mark a point on the floor, precisely level the tribrach, and center the image in the optical plummet.
Draw a pencil line on the tripod head precisely outlining the tribrach.
Rotate the tribrach 120 degrees and fit it to the pencil outline. Relevel.
Mark the point on the floor now indicated by the plummet.
Rotate another 120 degrees and repeat.
If you did things accurately, the 3 points will form an equilateral triangle.
Adjust the optical plummet to the center of the triangle.
Repeat entire procedure as a check.

> Thanks for the replies.
>
> I have the Seco adjusting ring with the spirit level. I seem to be having trouble with the small screws in the optical plummet adjustment.
>
> I think I have it figured out, but was wondering if anyone had an instruction sheet. I found one last night from a calibration class that Hayes put on several years ago.
>
> Thanks,
> Jimmy

Remember the adjustment is similar to the leveling screws on an old transit. You must apply opposite and equal adjustments to maintain tension on the optics. If the proper tension is lost the glass with the cross hair (or circles) will float and you will not be able to maintain proper adjustment.

Jimmy,
If you visit my web page you will find the diagram you seek. Tribrach Adjuster

I use the pencil on plate method for a check or to adjust in the field but much prefer the puck method over all. It is faster and gives me a better feeling in regards to precision. The placing of the tribrach over the tracing always leaves me a little uneasy.

> Start with the tripod head approximately level so not much motion is required on the tribrach screws.
> Mark a point on the floor, precisely level the tribrach, and center the image in the optical plummet.
> Draw a pencil line on the tripod head precisely outlining the tribrach.
> Rotate the tribrach 120 degrees and fit it to the pencil outline. Relevel.
> Mark the point on the floor now indicated by the plummet.
> Rotate another 120 degrees and repeat.
> If you did things accurately, the 3 points will form an equilateral triangle.
> Adjust the optical plummet to the center of the triangle.
> Repeat entire procedure as a check.

I use the same method, usually take less than 20 minutes.
EVERY crew chief should be able to do this... showing my age 😉

How About a Surveying Tips and Tricks Thread?

You know, it would be really groovy (yes, I'm old) to have a section on this board devoted to stuff like instrument adjustment procedures, etc., doncha think? A lot of us have learned many useful tricks along the way, or have come across links to useful information.

(I use the adjusting ring too. Which reminds me, it's about time I do some checking and adjusting on our stuff again!) :-$

How About a Surveying Tips and Tricks Thread?

Start it up and I will participate. I have been thinking of starting a tips and tricks thread for a bit.

Got to figure out some way to break down the topics right off the bat though so that things do not get all mixed together.

Maybe change the subject line for various tasks and then everyone can reply to that one, so like equip maintenance, concrete, hand tools etc?

I use this method also. Once you learn it and get comfortable with it, doesn't take much time at all.

All you need is a target on the ceiling of your office, two tribrachs and an adjusting cylinder. I recommend the one with the level bubble on it so you adjust both the plummet and the level bubble.

It's also great when the Management comes in and notices the target. They always want to know what it's for and you can make up all sorts of BS stories to keep them thinking, "those Surveyors are weird, I better stay away from them."

Put one tribrach on a tripod under the target. Put the cylinder in the tribrach. Put the other tribrach (to be adjusted) upside down on the cylinder. It does not matter if anything is level. Do what you need to do to aim the upside down tribrach plummet at the target on the ceiling. rotate the tribrach around, it should stay on the target. If not take out half the error. You loosen one capstan screw on the plummet and tighten the other. There are four screws. Be careful. It is sort of like the old four screw transits. Loosen one screw and tighten the other. Do this through trial and error until you can rotate the tribrach around and the plummet stays on the target. You are making the plummet perpendicular to the tribrach.

If you have cheap Chinese made tribrachs that you got for a hundred bucks, just throw them away and get more new ones. It isn't worth your time to mess with them because the cheap capstan screws will probably just break when you try to turn them anyway.

Dave has some advice, but let me add that the distance to the target on the ceiling has to be as far up as your highest expected tribrach height will be over the point in use; you cannot get too close to the ceiling.

Ken

Calculus formulas on the whiteboard is guaranteed to intimidate any engineer that enters the office.

Wendell, would you consider this?

> You know, it would be really groovy (yes, I'm old) to have a section on this board devoted to stuff like instrument adjustment procedures, etc., doncha think? A lot of us have learned many useful tricks along the way, or have come across links to useful information.
>
It will be very useful to newbies like me to have a category for tip and tricks! Mahalo!!