I'm a new user of a Topcon Tesla with Magnet software - coming from an FC-200 with Topsurv 7. I use -30 prism constant glass for backsites and -7 prism constant 360 prism forsite. I set the "class" in Magnet for -30 b.s. and -7 f.s. which works great EXCEPT when setting/checking the backsite. The Tesla sends a -7 p.c. to the instrument (Topcon PS) for the b.s. when it should send a -30 p.c.. I have to manually change the p.c. to -30 when setting/checking the backsite. Is there something I'm doing/not doing correctly?
I had similar issues with TopSurv 7.5 through 8.2. The best solution I found was to shoot the back-sight and check the distance. If it is off by the difference in the prism constants, toggle the prism constant setting from -30mm to -7mm and back again then re-shoot the back-sight distance. The gun usually catches the change after a couple of tries.
I surprised this issue with Topcon doesn't come up more often. I don't have Magnet, but I run Topsurv 8.2.3 on an FC-250, and it does the same thing (or at least something similar). On the previous version, I believe that it used the wrong constant, but the screen display would display the right one, and you didn't even know it was using the wrong one.
The way I get around it is to always use the same prism on BS & FS. That help prevent human errors too...
I agree, it's best to use prisms with the same constant. However, the ATP1 - 360 prism that comes with the robot is -7. I don't know of any -7 standard glass prisms that could be used for backsites.
> I had similar issues with TopSurv 7.5 through 8.2. The best solution I found was to shoot the back-sight and check the distance. If it is off by the difference in the prism constants, toggle the prism constant setting from -30mm to -7mm and back again then re-shoot the back-sight distance. The gun usually catches the change after a couple of tries.
The biggest issue is when storing the backsite point - like when first starting a project and storing backsite as found monument or traverse point.
I got screwed by this often enough that I learned to locate and store the back-sight point then toggle the prism constant setting and re-shoot the distance. If the second distance is not different from the first by the difference of the prism constants then it's likely that the instrument did not pick up the -30mm offset for the first shot. Oddly, mine would often ignore the change from the -2mm offset for the A7 prism to the -30mm for the round prism but when changing from the -30 back to the -2 it always made the change.
Edit: Once I made the switch to Carlson SurvCE I don't see this particular problem anymore.
My A7 prism is -2mm - the dealer thought I should just leave it set for 0mm!
I use the A7 prism only for topo, staking, things like that where I don't leave a backsite set up (I discovered the hard way not to leave a backsite set up when taking topo!).
I ended up replacing my other prisms (a mix of -30 & 0) with Seco nodal point mini prisms (-17.5mm)for boundary surveys. I screw the nodal point prism into the base of the A7 (leaving the A7 wrapped up) so I can mount the RC-4 unit on top. It's a little heavy, but I only use these with bipods or tripods anyway. This allows me to have a configuration where FS & BS are both the same and has been working well.
Topsurv 7, is kinda old, so I'm not sure when they added the option to store different BS/FS prism offsets. But under your Backsight, click on the settings icon at top. Toggle through settings. You can store your BS prism as -30mm and store the foresight prism as ATP1 which is -7mm.
Also in Magnet Field (predecessor to TopSurv), you can change the prism offset on the fly. In topo screen there is a prism height/offset icon in lower left.
I have a what could be a -0.20mm± Sokkia retro prism holder that came with a prism assembly from EBAY.
After puttin into use errors of closure were immediate and then I noticed the 5/8in threads were offset 0.04 from center.
It caused frustration and misery when mixed in with my -0.30mm setups.
> Also in Magnet Field (predecessor to TopSurv), you can change the prism offset on the fly. In topo screen there is a prism height/offset icon in lower left.
If I need to store the b.s. point (like the first setup on a project) I do change the prism constant on the fly. My problem is, ANY TIME I shoot the b.s., the prism constant SHOULD automatically change to the backsite p.c., but it doesn't. It only works correctly in the "set collection" routine. It doesn't work correctly in the "backsite setup" routine.
What version of Magnet are you using?
Under the Backsight routine, try toggle on "Fixed Height", even in 2d mode.
Image finally arrived
I took this pic with my phone and emailed it 27hrs ago, is arrived there minutes ago.
This is the odd prism holder, anyone know of a use for it?
Image finally arrived
It looks simialr to the old Leitz style (?) prism holder that we used to use back in the day before total stations.
