System 1200 Newsletter – No. 34 TPS1200 Check & Adjust
Contents
1. sight the direction the crosshairs in the telescope point and the line perpendicular to the tilting axis This error will affect all horizontal circle readings and increases with steep sightings The table below shows the influence of a c 10 line of sight error on the horizontal angle for different vertical angles TILTING AXIS ERROR A The tilting axis error is caused by the deviation a of the mechanical tilting axis from the line A e to the vertical axis The tilting axis error can be observed on a per fectly levelled instrument once the telescope is moved vertically along a vertical line e g an BU Surveying Surveying amp Engineering Division edge of a house the crosshair moves from the vertical line even though the instrument is not turned in HZ As the Line of sight error the Tilting Axis Error effects horizontal angle readings with increasing steep ness of the sighting but other than the Line of sight error has no effect on horizontal targets Again the effect to the vertical angle is very small and is usually ignored Shown below is the influence of a a 10 tilting axis error towards the horizontal angle for differ ent vertical angles Zenith angle Error in Hz 90 0 60 6 17 VERTICAL AXIS ERROR V The vertical axis error often referred to as stand ing axis error is not an instrument error but a set up error It occurs if the vertical axis is not in tru2. 1 t Compensator index error determination e V index error determination e c Line of sight error e ATR zero point error determination This is done by measuring to any point located approximately 100m away which is at approxi mately the same level this is to avoid influ ences of the tilting axis error when determining the line of sight error If the instrument does not have an ATR or if it is not necessary to determine the ATR corrections then the remote target need not be a prism However if the ATR is being calibrated then the target must be a standard round prism such as the GPR1 this is even if a 360 prism or any other prism is being used for measurement work Always take greatest care when manually aiming at the target Within the Combined Adjustment the target has to be aimed at in both faces several times in order to average the aiming errors From the second repetition onwards the standard devia tion of the measurements is displayed for quality control 11 40 IR gt El TOOLS sto LL a lt amp Adjustment Accuracy x No of Heas 3 ao 1 Comp 0 0000 gq ao t Comp 0 0000 gq o i V index 0 00027 gq oc Hz col 0 0001 g o ATR Hz 0 0030 g ao ATR 0 0011 g lat CONT HEAS DETERMINING THE TILTING AXIS ERROR Since the tilting axis error has only an effect on steep sightings it can only be determined with observations to targets located either signifi cantly below or above the leve
3. example no strong heat shimmer measure in the morning or with overcast sky e Level the instrument precisely using the elec tronic bubble e The instrument tribrach and tripod should be secure and firm e Ensure the instrument and tripod are not exposed to direct sunshine this may cause one sided heating of the instrument or tripod Before starting the calibration routine also en sure that the instrument had enough time to when it has to be right Seica Geosystems System 1200 Newsletter No 34 TPS1200 Check amp mages adapt to the ambient temperature As a guide the time for acclimatisation should be at least 20 minutes or 2 minutes per 1 C 1 minute per 1 F of temperature difference between storage and working temperature A LITTLE THEORY To understand the instrument errors of a total Station it is important to know the instrument axes and the essential relationships between them e The Line of Sight L should be perpendicular to the Tilting axis T e The Tilting Axis T should be perpendicular to the Vertical axis V e The Vertical Axis V often referred to as standing or trunnion axis should be perfectly vertical Any imperfections in the conditions above will result in instrument errors which will affect measurement accuracy LINE OF SIGHT ERROR C The line of sight error often referred to Hz collimation error is caused by the deviation c between the optical line of
4. System 1200 Newsletter No 34 TPS1200 Check amp Adjust THE IMPORTANCE OF CALIBRATION To achieve the highest measurement accuracy from total stations the calibration of the instru ment is essential A badly calibrated instrument may not measure to its specified accuracy which may in turn result in points not being measured to the required or expected accuracy Accurate measurements with total stations as sume that all instrument axes are perfectly per pendicular to each other This requirement can almost certainly never be attained and certainly never retained over a period of time this is a mechanical limitation faced by all instrument manufacturers This newsletter focuses on the determination of these instrument errors commonly referred to as the calibration of an instrument Within TPS1200 instruments the calibration routine is called Check and Adjust and is found in the Tools Menu panel Combined Tilting Axis a Compensator 1 t Current Values End Check amp Adjust Att CONT CONF The Check amp Adjust routine is extremely easy to use and takes only a few minutes it is even possible to create a logfile of the results of the calibration The instrument errors that can be determined using the Check amp Adjust routine are e c Line of sight error a Tilting axis error e _ t Compensator index error e I Vertical Index error e ATR Hz zero point error e A
5. TR V zero point error BU Surveying Surveying amp Engineering Division WHEN TO CALIBRATE During the production process of the total sta tion instrument errors are determined and set to zero however the instrument will still need to be calibrated on a regular basis In addition to this regular calibration of the in struments additional calibrations should be made e Before first use the instrument may have had a long journey with large temperature dif ferences e After long periods of work or after long storage periods e After large temperature difference it is strongly advised to recalibrate an instrument if the working temperature differs by more than 10 C 18 F from the temperature which existed at the previous instrument calibration This includes re calibrating if there is a large difference between the storage and working temperature e After rough or long transportation me chanical shocks always take measures to protect the instrument from shocks e Periodically for high accuracy job sites WHAT HAS TO BE CONSIDERED WHEN CALIBRATING Once calibrated all measured deviations are automatically applied to every measurement If the calibration routine was therefore inaccurate this will then adversely affect all subsequent measurements So do the calibration properly accurately and follow the advices below to determine instrument error values precisely e Good atmospheric conditions for
6. ally e Circular bubble on instrument and tribrach e Visible red laser beam RL EDM For the mechanical adjustments please refer to the TPS1200 user manual BU Surveying Surveying amp Engineering Division It is worth to note that particularly when measur ing with the reflectorless EDM to edges or in clined planes a divergence of the visible red laser beam from the line of sight can lead to measurement errors this is because the RL EDM will not measure exactly to where the in struments cross hairs are being pointed The red laser beam must therefore be periodically ad justed OTHER INFLUENCES TO ACCURACY Careful calibration and adjustment is certainly required to achieve the most accurate measure ments but does not guarantee them There are many additional factors which can affect the measurement accuracy e One sided instrument and tripod warming e g from sunlight use an umbrella e Heat shimmer and unpredictable refraction e Instrument has not acclimatised to surround ing temperature In addition when the highest precision measure ments are required it is strongly recommended that two face measurement techniques are used Two face measurements eliminate most instru ment errors also inaccurate determined instru ment errors through averaging the measured angles AND FINALLY Always remember a total station is at the end of the day a high precision instrument that must be handled with
7. great care Seica Geosystems when it has to be right
8. l of the instrument when it has to be right Seica Geosystems System 1200 Newsletter No 34 TPS1200 Check amp Adjust To avoid influences from the line of sight error the combined adjustment has to be run prior to the tilting axis calibration The tilting axis error determination does not need a prism or target plate being aimed at This means that this adjustment can be made at any time select any recognisable point which is as far away from the instrument as possible and is well above or below the instrument maybe a detailed point on a high building ensure this point can be accurately aimed at twice CHECK amp ADJUST CONFIGURATION Remember it is possible to create a logfile for the Check amp Adjust routine select the appro priate format file as for any other application Additionally it is also possible to configure the instrument to remind the user to perform a regu lar calibration at regular intervals press F2 CONF in the TOOLS Check amp Adjust Menu panel As a default this reminder is set to 6 months Configuration Parameters Logtile Adjust Reminder CPT At cont PAGE The reminder period is only reset once both the Combined and Tilting Axis calibration routines are completed MECHANICAL ADJUSTMENT In addition to the instrument errors mentioned above some adjustments cannot be arithmeti cally corrected and therefore have to be adjusted mechanic
9. ly plumb It is important to note that unlike the Line of Sight error c and Tilting Axis error a the Verti cal Axis error affects both horizontal and the vertical angle readings and can not be elimi nated by two face measurements The vertical axis error can be avoided by very carefully levelling the instrument Alternatively it can be compensated for with the in built two axis compensators this then means the levelling only has to be done roughly as the fine levelling is arithmetically corrected by the compensator COMPENSATOR INDEX ERROR L T The compensator index error is the deviation of the zero point of the compensator from the plumb line With a dual axis compensator the index error of the compensator is divided into two components one parallel longitudinal 1 and the other cross wise transversal t to the telescope represented as c and d in the graph below when it has to be right jteica Geosystems System 1200 Newsletter No 34 TPS1200 Check amp Adjust The longitudinal compensator index error P is similar to the V index error and affects only verti cal angle readings The transversal compensator index error t is similar to the tilting axis error and mainly impacts the horizontal angle The impact on the angle increases with steep sight ings VERTICAL INDEX ERROR I coms l A vertical index error exists if the 0 mark of the vertical circle reading does not coincide wi
10. th the instruments mechanical vertical axis The v index error affects all vertical angle read ings independent of the steepness of the aiming but has no impact on the horizontal angle ATR COLLIMATION ERROR The ATR collimation error is the angular diver gence between the telescope center crosshairs and the center of the ATR camera The Hz component of the ATR collimation error affects the horizontal angle whereas the V com ponent of the ATR collimation error affects the vertical angle Always remember that when measuring with ATR the crosshairs may not be exactly on the prism centre even if the ATR is newly calibrated This is not an error as the divergence to the centre of the prism is measured by the ATR and the angles are automatically corrected These deviations can be particularly seen when measuring with EDM mode FAST the instru ment positions only roughly to save time and corrects the remaining divergence by the ATR UsING TPS1200 CHECK amp ADJUST As already mentioned before starting the Check amp Adjust routine ensure that the conditions are appropriate for a calibration to be made and the instrument has acclimatised to the surrounding temperature BU Surveying Surveying amp Engineering Division The Check amp Adjust routine is extremely simple to use simply follow the instructions on the screen COMBINED ADJUSTMENT The combined adjustment simultaneously de termines e
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