A friend of mine has a nikon total station that it is not callibtated since 5 years now. Is there any way to check how many cc is missing or to prove that is make wrong measurments?
Few things you can try.
Not sure what cc is?
Do you have a calibrated baseline nearby?
Need to be forced centering, preferably on pillars.
Set up your own base with 2 targets (in tribrachs) and measure total distance from both ends, and individual measurements from say 5 metres behind one on same line to near and far, then repeat setting up between the two.
Make your base as long as you can.
I'd repeat on a short base also.
That would give a quick check.
I'd do a standard on board Nikon calibration first and see what the horizontal and vertical errors are reported.
It's worth checking measurements on both faces, and recording horizontal and vertical components.
I also check the computed reductions just in case there is some silly display error.
Horizontal and verticals could be checked by repeating several readings to same point.
I'd set a different back sight reading and repeat same, doing this several times again to check for errors.
Turn off and take the instrument off the tribrach. Re affix and repeat.
I found once my Nikon 821 got a bit cranky when I tried to eke out more from a very flat battery.
So suggest you use fully charged ones.
If you have a mate with another EDM have him/her help out with comparisons.
Don't use two targets - use one only and read in each position in turn. That way you eliminate any inbuilt target error and have the instrument adjusted to that specific target/prism combination.
(AB + e)+(BC + e)= AB+BC+2e . Subtract (AC + e) to get "e" the instrument/prism error constant.
When I'm certifying swimming pools I do this check within the pool area immediately before the survey, as this then also allows for any atmospheric problems due to the high humidity and temperatures.
Typically with our fully calibrated instrument (a GDM640 kept just for this type of work) the variations on each distance are very small (0.1-0.2mm) and the instrument/prism constant is working out at around 0.4mm.
Note that if you measure an overall distance by setting between the two points and measuring each way then you double the error constant, which is why it is important to know what it is and to set it in the instrument.
Once you have done so, measure one of the lines again, to check you haven't put the wrong sign on the constant!
Chris I'd never set a constant to one prism.
What happens if you have multiple prisms out on a job, set up all around you.
Don't have any issues with your reply to calibration, just curious.
I send my Nikon back to be calibrated and serviced but don't tinker with settings except for reflectorless measurements and prism constants.
I have one prism that's about 1.5 mm different to others, but generally rest are within tolerances that get swallowed up in other standard error ellipses.
I don't want to get of on a super accuracy standard argument.
I'm curious about your certificate of measurement of a swimming pool. Do you show mm or tenths of mm?
I recently setout an international soccer ground (kerb lines) and the builder wasn't too concerned about a couple of centimetres either way.
I was, but left that to him to sort out if anyone queried.
Sorry johnymal. Not wanting to hijack your issue with sidetracks.
One could say that calibration is double checking that the instrument makes the same measurements as it did from the factory.
That said, I calibrate my instruments every week because I check it against some of the same information that I have been gathering for over 30yrs.
It may not be a full blown certified test, it does keep me aware of the shape of things.
Nothing is wrong with annual checkups and nothing is wrong if you on occasion do them yourself.
0.02
For most purposes just knowing that the prisms are all in reasonable agreement is adequate, but if there is possibility of an argument, you might as well be prepared by knowing that your set-up is absolutely right.
All our prisms get an occasional check using a forced-centred line and compared with our calibration prism. That way we know if there are any variations and on a job which might require higher levels of accuracy we can pick compatible prisms to use.
Every three years our calibration instrument and target go off to a Mekometer calibrated baseline to get an absolute calibration certificate. We then use that instrument to measure a local (8 point 900 metre) line we have set on a dam wall. This is used to check all our other instruments, including the GPS, and the derived prism constant and scale factors are set into the instruments.
For soccer pitches (and, I assume similar sports) I seem to recall that the specification is more concerned with the pitch being rectangular and there is quite a lot of leeway in length and width, compatible with using a stretchy tape to mark things out. A little different in athletics, where I think the track length is measured 30cm. into the track from the inner kerb edge.
As regards swimming pools, because the overall lengths are relatively short and longer distances consist of multiple times the basic length any error becomes rapidly multiplied (1500 metre in a 50 metre pool gives a 30X error). The FINA standard is -0mm/+10mm. between the touchpads.
I set the baselines up to 0.1mm. but the actual values are recorded on the certificate to 1mm., since there are so many imponderables. There's a paper on our website www.SCSsurvey.co.uk which can be downloaded and which covers some of the problems. It's due to be rewritten as in the intervening time many more problems have been unearthed, mainly to do with moving bulkheads and touchpad seating.
Back to the original question. It only takes three tripods and about 20 minutes to carry out the check, so it's well worth doing in spare moments. If you find the constant starts to drift a lot it is an early indication that the electronics are ageing.
Note: Calibration is defined (roughly) as obtaining the corrections which must be applied to any reading to bring it to the correct value as determined by some standard.
Checking is defined (roughly) as seeing if everything is measuring within the expected parameters.
I read your question as asking for a quick check. I suggest that you manually measure a distance +/- 100 feet using a metal tape. Then occupy one end and electronically measure the distance. If they compare within reason all is good. If the measurements don't compare well then you need to calibrate everything. Your tape, your EDM and each prism.
> A friend of mine has a nikon total station that it is not callibtated since 5 years now. Is there any way to check how many cc is missing or to prove that is make wrong measurments?
One simple way is to have it calibrated by someone qualified to do it properly. If, by your question, we are to assume that's not an option, then there is a TON of information already posted on this site on how to go a long way to determine if it is within specification.
Most of the replies talk of the EDM only. If that's all you're interested in, then that's fine, but if it's pointing accuracy, then start here:
https://surveyorconnect.com/index.php?mode=thread&id=275706#p275713
Buried in that thread and about a half a dozen that follow, is a step-by-step procedure to do what you're asking. Good luck!
Imagine over the time span of 30+ years comparing the measurements of a half dozen TS between the same points.
That includes angles and distances between 4 points in open sight of each other. Yes, as a whole, that makes many combinations.
Every TS I use and/or purchase gets that comparison just to check out the technician's settings and what may have occurred during shipping.
It is also a part of the test track for a crew member that wants to step away from their brush ape title.
Equipment need the same attention to their cleaning and lubrication and probably most of all the proper handling between box and measurement and return to box.
My answer to your question - one of the best quick checks is to measure between two points that you know the correct information.
B-)
I understand Chris' notion based on principles from the scientific method to fix as many variables as possible when trying to identify a source of error. However, I have always run the baseline procedure using multiple targets. Of course, you have to be sure that your other tribrachs and prisms are in good working order. I suppose if I encountered some sort of anomaly I may redo the procedure utilizing only one target to eliminate error sources, but in the interest of saving time I typically run a baseline calibration with multiple targets.
Isn't the calibration baseline system set up specifically to check at different distance intervals? I don't see how checking one distance really verifies anything. The one I use has 0m, 100m, 400m, and 1000m stations as well as a -100' station for steel tape calibrations. The procedure specifies that you verify distance measurements from:
0m-100m
0m-400m
0m-1000m
100m-400m
100m-1000m
400m-1000m
cc refers to angular measurement. It is 0.0001 grad, or about 0.3" of a 360° circle. c is 0.01 grad, or about 32". My gyro (old) is graduated to 0.01 grad, or 1 c.
I use grads in my computations, adjustments, and database, much easier to deal with mathematically because it is decimal, not sexagesimal.
Multiples of 100 metres has some disadvantages, especially if you are looking at older phase comparison instruments where a cyclic error might also be present.
The baseline we use has distances of 0,5,123,231,358,477.5, 594 and 900. Measurements are carried out from 0 and 5 to all the other positions and this provides a spread of distances covering all whole metres from 0 to 9.
Fair comment by those who mention that angles have been ignored. We would normally carry out the standard GDM/Trimble tilt axis correction tests at a regular interval. Remember to record the values as hard copy so you can identify any trend.
The comment about in and out of box is very relevant - I'd agree entirely. We have a policy of "if you need to move your feet then put the instrument in the box". Even two paces are enough to trip up and drop it.
Cc
Thanks John
Old dog, new tricks. If I've ever known that I've long forgotten.
Nearest I got to grads was the key on the 41 etc.