Why do Total Stations need to be Calibrated?
Total Stations should have an independent check and adjustment performed on them at least once a year or at a point that you feel that the total station you are using is not giving the accuracy you expect it too. This is termed as a Calibration. The Calibration Certificate gives confidence to other people using the data you have collected or the data you have used with the Total Station that the total station can perform to the stated accuracy.
Why do you need to check a Total Station?
But having a calibration certificate only means that the total station was accurate on the day it was independently checked. It doesn’t mean that it still is correctly adjusted and giving accurate angles and measurements. As a side note, I have had a Leica TCRP1205 that has had a calibration certificate yearly but has not been adjusted since 2010 (9 years ago), the total station gets put on the test rig and just lines up year after year. A Total Station should be checked at least once a month or before any precise work is to be carried out.
What checks need to be carried out on a total station?
The six checks that should be performed on a Total Station are: –
6) EDM (Distance Measurement) Check.
The checks done in this list will be dependent on the Total Station you are checking, but before checking a Total Station, it is prudent to check the wooden tripod being used.
Why should you check the wooden tripod first.?
All these checks should be performed on a suitable wooden tripod that will support the total station that is being checked or used. Ensure that you have checked your survey tripod, here is a check procedure for the survey tripod. If your tripod is not in a good condition, then the total station checks being undertaken will be poor and lead you to think that the total station needs calibrating.
Top Tip for doing these Total Station Checks.
To make these checks easier it best to set the total station up over a known point with a long clear sight to at least one other known point. Also use the same location for the checks as long as the known points haven’t been disturbed. If multiple total stations are being checked, using the same known points will give great confidence if all the results are the same.
Total Station Check No. 1. The Plate Bubble Check.
These are not on many of the modern total stations. Most modern total stations only have the circular vial which still needs to be checked. You may also find that your total station has an electronic plate bubble, but the procedure will still be the same.
1) Set up the instrument on a sturdy tripod.
2) Turn Total Station until the bubble tube is parallel with 2 of the footscrews, and level the bubble carefully.
3) Turn the Total Station through 90 degrees, and level the bubble using third footscrew carefully.
4) Turn the Total Station back through 90 degrees, and re-level bubble if necessary. Keep repeating this process until you are confident the bubble rests in the centre.
5) Then turn the Total Station through 180 degrees. The bubble should be central if correctly adjusted.
6) If the bubble does not stay central, then you are best advised to have it adjusted, or repaired, and calibrated by your specialist survey equipment supplier.
If you only have a circular vial then the check will be the same process as above but you will be aiming to keep the bubble in the center of the vial. If it does not stay in the center, then again you are best advised to have it adjusted, or repaired, and calibrated by your specialist survey equipment supplier.
Total Station Check No. 2. The Optical Plummet Check.
There are two types of optical plummets and some total stations have a laser plummet instead of the optical plummet.
This check method is for the fixed in Tribrach optical or laser plummets.
1) Having set up the Total Station and checked the Plate Bubble as described above, level the tribrach with Total Station or plate level over a point defined by a cross (the finer the cross the better).
2) With a sharp pencil trace the outline of the tribrach base plate on the tripod head.
3) Release the retaining screw slightly and carefully turn the tribrach through 120 degrees keeping within the marks on the tripod. Re-level and sight the cross and note if the cross is not in the centre.
4) Repeat, turning through a further 120 degrees. The cross should be central each time.
5) If the cross is not in the centre each time then you are best advised to have it adjusted, or repaired, and calibrated by your specialist survey equipment supplier.
This check method is for the revolving plummet, the kind that are fixed in the total station.
1) Having set up the Total Station and checked the Plate Bubble as described previously, level the tribrach with Total Station or plate level over a point defined by a cross (the finer the cross the better).
2) Level and centre over a point defined by a cross.
3) Rotate the Total Station through 120 degrees and observe the cross. The cross should remain central.
4) Rotate the Total Station through a further 120 degrees and observe the cross. The cross should remain central once more.
5) If the cross is not in the centre each time then you are best advised to have it adjusted, or repaired, and calibrated by your specialist survey equipment supplier.
Practical Tip for the total station plummet check.
Having set up above a known point just spinning the total station with the laser plummet on, you should see that the laser dot stays in the same position and not move away from the centre of the nail significantly.
Total Station Check No. 3. The Horizontal Circle Check.
1) Set up and level the instrument.
2) Select and sight a well-defined distant point, this should be at least 100m away and you should also be careful to ensure a clear line of sight (A cool overcast day would be ideal). Read the Horizontal angle scale (H1) and note down your reading.
3) Transit the telescope and re-sight the same point on the opposite face. Read the Horizontal angle scale (H2) and note down your reading.
4) Work out the difference between H1 and H2. The difference between H1 and H2 should be 180 degrees. However, your angular error should be less than the stated accuracy of the Total Station.
For example, H1 = 180 degrees 0 minutes 0 seconds. H2 = 0 degrees 0 minutes 3 seconds. Then (H1)-(H2) =179 degrees 59 minutes 57 seconds. This is a 3 second inaccuracy. If the Total Station is classed at 5 second accuracy, then the result would be acceptable.
If the result is greater than the accuracy stated on the Total Station then you are best advised to have it adjusted, or repaired, and calibrated by your specialist survey equipment supplier.
Total Station Check No. 4. The Vertical Circle Check.
1) Set up and level the Total Station as before.
2) Select and sight a well-defined elevated point. Again this is best done on a cool and overcast day.
3) Read the vertical angle scale (V1) and note down the reading.
4) Transit the telescope and re-sight the same point on the opposite face.
5) Read the vertical scale (V2) and note down your reading.
6) V1 and V2 the abstract angles of elevation or depression should total 360 degrees.
For example, V1 = 100 degrees 0 minutes 0 seconds. V2 = 260 degrees 59 minutes 57 seconds. Then (V1)+(V2) =359 degrees 59 minutes 57 seconds. This is a 3 second inaccuracy. If the Total Station is classed at 5 second accuracy, then the result would be acceptable.
If the result is greater than the accuracy stated on the Total Station then you are best advised to have it adjusted, or repaired, and calibrated by your specialist survey equipment supplier.
Total Station Check No. 5. The Trunnion Axis Check.
1) Set up and level the instrument as before.
2) Sight a well-defined high level point with the centre of the cross hairs (like a steeple or a fixed radio mast.
3) Depress the telescope and read a tape set (perpendicular on the floor) close to the instrument (T1) and record your reading.
4) Repeat on the opposite face and read the tape again (T2).
5) The readings T1 and T2 should be equal.
If the result is greater than the accuracy stated on the Total Station then you are best advised to have it adjusted, or repaired, and calibrated by your specialist survey equipment supplier
Total Station Check No. 6. The EDM (Distance Measurement) Check.
1) Set up a well defined distance between two know points, ideally over 30m. Two hilti nails would suffice, ideally at the same level.
2) Measure the distance accurately with a steel tape.
3) Set up and level the instrument as before over one of the hilti nails.
4) Using a prism on the far hilti nail, measure and record the distance.
5) Compare the readings from the steel tape and the distance measured by the total station. This is a gross error check for distance measurements and errors of the order of 2 or 3mm will usually be acceptable.
6) If the result is greater than the accuracy stated on the Total Station then you are best advised to have it adjusted, or repaired, and calibrated by your specialist survey equipment supplier
Leica Total Station Check and Adjust Programmes.
Leica Total Stations, like the TCRP1205 I use, have a check and adjust programme installed that can be run to fine tune the instrument. It is important to remember that this programme does not replace the need to have an independent calibration done on the total station. The programme is easy to use provided you have a large open space and a good quality prism station. Carrying out the check and adjust programme should be carried out before the first use, before any accurate survey work is to be carried out and after prolonged storage or rough transportation.
Tips for carrying out the Leica Check and Adjust Programme.
Carrying out the check and adjust programme is best done on an overcast day with good visibility. An overcast day will reduce the risk of heat haze affecting the results and the accuracy achieved. A genuine leica prism station will yield the best results when carrying out the check and adjust routine. The prism station will have to be placed at least 100m away from the total station for the first set of tests to be done and then at a suitable distance either above or below the total station for the optional tests.
Running the check and adjust programme will alter the target recognition values within the Total Station, and provide new accurate readings to the prisms used. Before accepting these new readings you can see what the previous settings are before applying the new adjustments. The more time and care you take with the above checks, the better the accuracy you will be able to achieve with the Total Station you are using.
