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Trouble with Trimble S7 Holding Zero while performing high precision radial , after wathstakeout
Hi, I’m new here and was hoping to get some opinions from some of you who may do similar type work and have experienced similar problems in the past.
We started a large structural staking project about a month ago using a Topcon QS-3 robotic total station. We have completed several similar projects on the past and as usual, we had the instrument cleaned and calibrated a couple days before starting.
To start off, we ran a traverse through the building site setting control in areas that would be safe until the slab would be poured, in doing this, we quadrupled angles and distances in direct and reverse and averaged to calculate coordinates. As usual when using this method, the traverse closed incredibly well.
On the first day of staking (instrument set up on compacted red clay, very firm, over a 24″ long, 5/8″ iron pin with cap) I noticed something stranger going on with the horizontal angles. We were staking points radially and robotically from control within our closed traverse. After being setup for about 45 minutes and setting about 6-8 points, we checked into the first point we set, missing the line by .025 (when setting these points, we use a mini prism and a 1link pin pole which has been confirmed to be precisely plumbed), theseoints were set within a tolerance of .010′. After seeing the error in the check, I turned to the backsight and found that the horizontal angle was reading about 35″, gun was within 30″ all the way around of being level and had not been moved off the point, compensators wre enabled.
After playing with the gun for countless hours and testing its ability to hold a good zero on the backsight, I found that over and over, after turning and looking at different points over a period of 15-30 minutes, the gun would be missing the backsight by 20-30″ every time.
I have checked accuracy of the digital level by turning 360 in 90 dog increments, it’s wothin 10″ everywhere, I have checked for play on the tribrach and in the legs at the joints and hinges and found that everything is as solid as it can be. I trust the stability of the ground as it is good firm clay that allows for good penetration with the legs.
Now, the only potential issue I know of is that the weather was cold, frozen ground when setting up and very slow thawing with sunshine but still below freezing temps. That said, it clearly isn’t affecting the setup too much or my level would be going crazy, and even then, the compensators should take care of that.
On top of all of this, I took a brand new, freshly calibrated Trimble s7 robot to the same site sat on the same point in almost identical weather conditions and found that it had the exact same problem, although when using the Trimble, I turned the angles and shot the distances manually instead of robotically.
Any ideas??
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14 Replies
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John Simmons, post: 353271, member: 11006 wrote: Now, the only potential issue I know of is that the weather was cold, frozen ground when setting up and very slow thawing with sunshine but still below freezing temps. That said, it clearly isn’t affecting the setup too much or my level would be going crazy, and even then, the compensators should take care of that.
This may be your problem. Setting up on frozen ground (frost) without any special precautions can cause this. The narrow points of the tripod feet will slowly sink in unevenly, throwing off your instrument rather quickly regardless of temperature.
You can try using “feet” (blocks of wood, plastic or metal) to spread out the load. Lo-ink sells a plastic set that I use sometimes. I think they also have some platforms that attach to rebars that you drive in the ground – your tripod feet set on these platforms and that keeps them stable. I have never tried this one however.
Hmmm… I’ve got a 72 corner house foundation to pin tomorrow. But I think there is crushed stone there that I can set on.
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Clearly I made a typo on the thread name, oh well, can’t figure out how to edit it.
Thanks for the info, have u had this problem before and been able to resolve by using stabilizers for your tripod feet?
Either way I will certainly try this and see if it helps, I’ve thought and thought about what it could be that is causing it, I assumed it was an instrument problem until the problem repeated itself with the S7.
Might also mention that the same S7 operated without any problem whatsoever a couple days later when it was cloudy and upper 40s all day with dry ground.
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It’s got to be a freeze/thaw problem. Can you set three really long hubs for the feet to sit on? What I’ve don’t before is place the instrument over the pont and where the 3 feet marks are on the ground I bang in 3 long hubs on an angle so the tops are facing inward toward the point slightly. (In line with the angle of the legs going into the ground). That helps direct the weight into the hubs. The other benefit is that you almost certainly have hubs with you when you’re out there. Plus they stay there and you can use them again and setting up is a little faster because you know you’ll be over the point if you put the feet on those hubs.
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Setting on thawing ground is always a problem.
My most recent setup under those conditions was a location on a sand and oil mixed roadway in the middle of a traverse of 92 acres. The temperature was rising quickly mid day as the clouds parted and the sun appeared. The angle never repeated and I used the average of 8 readings and their flop equivalent that fell in a 20sec range and I constantly checked and adjusted digital leveling and centering.
Setting up over a root of a tree that is swaying in the breeze or other underground structure that has movement will give the same results.
0.02
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Have similar problems with freeze/thaw, even with below freezing temps when strong sun shines on one or more legs. Setting up on hubs is one solution that works, though getting them into frozen ground is a pain. Piling snow around the feet is my standard fallback procedure, when there’s snow… Anything you can do to insulate the feet to keep them from conducting any heat into the ground will help. A sunny vs. overcast sky will make a big difference in how much the tripod legs heat up.
Willy -
Here is the deal with the S Series instruments:
- First off, the rule of thumb is to let them acclimate for 1 minute per each degree Fahrenheit – so it’s best to take the batteries out and pack it in the back of the truck.
- Second, make sure your legs are sufficiently and EQUALLY spread apart as best as possible. (Your problem indicates that your legs may be setup too narrow – try to be at about 60 degrees from the surface.)
- Third… SurePoint will compensate up to 6′ of “tilt” in the instrument. If you’re still having problems, run the Compensator Calibration (General Survey > Instrument > Adjust Instrumet) and be sure to have a good setup when doing it
I might try one of these solutions: http://surveying.com/Products/Instrument-Tripod-Accessories/Tripod-Stability
How much work is going on on site? If they’re running a compactor anywhere, you’re gonna have a bad time.
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You’re not staking robotically and then looking through the instrument to check are you?
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SurveyAK, post: 353321, member: 9968 wrote:
- Third… SurePoint will compensate up to 6′ of “tilt” in the instrument. If you’re still having problems, run the Compensator Calibration (General Survey > Instrument > Adjust Instrumet) and be sure to have a good setup when doing it
I might try one of these solutions: http://surveying.com/Products/Instrument-Tripod-Accessories/Tripod-Stability
How much work is going on on site? If they’re running a compactor anywhere, you’re gonna have a bad time.
Really appreciate the info!
There is work going on but no compacting and were able to keep everyone off our control as we have set it within the building pad and outside of disturbance areas for foundations.
As for surepoint, I am new to Trimble and will be learning more about that and other technologies the S7 offers next week when we have a full day of operations training. I have seen a lot of inconsistency with the topcon equipment we have used in the past and I just don’t trust them to deliver precision like I need for this project and others without having to constantly relevel rebacksight and recheck after just a short period of time.
All that said, should the compensators in the S7 along with the surepoint technology not take care of the angular error accumulation from the movement of the legs?
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eddycreek, post: 353323, member: 501 wrote: You’re not staking robotically and then looking through the instrument to check are you?
When using the S7 I had worked for about 15 minutes robotically after getting a backsight, but when I noticed the angle had drifted I had started running it manually just because we had some construction traffic running back and forth thru our line of site.
As I said earlier I am still learning about the Trimble technologies, are Asking because of the different lenses the S7 uses? The way it was explained to me is that the lens used for the prism with the diodes is offset, therefore when looking thru the instrument it will be looking off center of the rod but is applying a known correction for the angle being observed when tracking that particular prism.
Further explanation on how that technology would be more than welcome although I might should start a separate thread for that.
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What eddycreek is saying (I think) is that on the Trimble robotics the cross-hair will not be centred on the target when in autolock.
The instrument doesn’t use the cross-hair. The autolock sensor has it’s own optical centre.Having said that, when it is calibrated, a reading on autolock and then on manual should be exactly the same.
The surepoint cannot compensate for everything. eg if the legs settle then the instrument position will move slightly, also a twist could be introduced into the top of the tripod which cannot be adjusted out without retaking the backsight.
You should notice any settlement on the level bubble though. I suspect slop in the tripod or tribrach but you are happy that these are perfect?
I like to get the tripod feet fully embedded, I notice it holds the angle a lot better than when the tripod feet only have point contact.Temperature changes will not help either. Let the instrument and tripod acclimatise for an hour. (I think you have already done this)
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A couple of possible issues I see here, are the legs being set too deeply, which can cause uneven pressure and thus movement, the sunshine in cold temps will move it all over the place.
I would never wait 45 minutes and 5-6 points before checking the backsight, and I wouldn’t set anything that had to be 0.01 tolerance or less, radially.
We would pick the two longest points on a line, set them radially, then occupy/back those two, and then adjust them when shooting between them. From there, we basically traverse around the building, and we check our distances by shooting diagonals where applicable.
This is just the way my outfit does it. Doesn’t make us more right, but we get really good results. -
>”All that said, should the compensators in the S7 along with the surepoint technology not take care of the angular error accumulation from the movement of the legs?”
The best instrument can’t accommodate bad procedure or unpredictable conditions. I think what you have is frost related.
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squowse, post: 353344, member: 7109 wrote: What eddycreek is saying (I think) is that on the Trimble robotics the cross-hair will not be centred on the target when in autolock.
The instrument doesn’t use the cross-hair. The autolock sensor has it’s own optical centre.Having said that, when it is calibrated, a reading on autolock and then on manual should be exactly the same.
The surepoint cannot compensate for everything. eg if the legs settle then the instrument position will move slightly, also a twist could be introduced into the top of the tripod which cannot be adjusted out without retaking the backsight.
You should notice any settlement on the level bubble though. I suspect slop in the tripod or tribrach but you are happy that these are perfect?
I like to get the tripod feet fully embedded, I notice it holds the angle a lot better than when the tripod feet only have point contact.Temperature changes will not help either. Let the instrument and tripod acclimatise for an hour. (I think you have already done this)
Exactly. If you turn the angles robotically with the controller and then try to look through the instrument to check your backsight it most likely will be offline.
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