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TOPCON GPT3005W - trouble doubling angles

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(@csparages)
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When doubling angles in Repeat mode, errors increasing with use. We had the gun calibrated in November....worked great in this mode for a while...now we have increasing errors when doubling angles. Has anyone run into this before? Your help and suggestions are greatly appreciated...

 
Posted : January 10, 2014 2:10 pm
(@maumic82)
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Had a similiar problem a few weeks back using a Leica TS05 I believe? It was a clients instrument. Come to find out the tribrach was bad and it had some slop in it. When the instrument was turned it would shift slightly inside the tribrach and therefore not show the correct angle in the gun.

 
Posted : January 10, 2014 2:52 pm
(@john-harmon)
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I have same trouble with collimation not holding.

 
Posted : January 10, 2014 3:12 pm
(@troy-deato)
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If the angle error that you get fluctuates...
Most of the time the problem is looseness in the tribrach or the tripod. The easiest way to isolate where the motion is to sight a point 200-300ft away and zero the H angle. As you look through the telescope of the instrument apply a little pressure to the tripod leg (*Normally just using your pointer finger*) As you apply the pressure you will notice that the cross hair will move L or R based on the direction that you apply the pressure. When you release the pressure the instrument should return to the (0) position optically. If it doesn't return to the 0 position you have found the problem. If the tripod is stable apply pressure to the Upper Tribrach Plate (Above the leveling screws and below the instrument base ) If this is stable the base of the instrument maybe loose in the Upper Tribrach Plate.
If the angle error is consistent (20" every time you double)that is collimation error and there is no need to check for looseness.

 
Posted : January 10, 2014 5:41 pm
 RADU
(@radu)
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Could also be tripod leg moving ... tripods legs can be thought to be clamped, but even heat, ok cold in your hemisphere on wooden legs and metal component could allow a miniscule change so get slippage as motor rotates TS and applies torque onto legs.

RADU

 
Posted : January 12, 2014 4:53 pm