Why is my Topcon LPS losing track of the Ligchine on these big outdoor pours?

The stuttering you're seeing is almost certainly caused by the **Line of Sight** (LOS) being broken by that pump boom, which triggers the machine's safety or 'lost signal' logic. Total stations are incredibly precise but they're sensitive to those quick interruptions. Every time the boom passes trough, the machine loses its vertical and horizontal reference for a split second, and the hydraulic valves usally freeze or jump as they try to recalibrate while the screed is still moving forward.

Raising the total station is a solid move. If you can get it on a tall tripod or even a platform that puts it six or seven feet up, you might be able to shoot over the pump's main elbow. But the bigger issue is usually the placement relative to the pour sequence. You want to position the total station in a spot where the pump doesn't have to sweep through the line of sight to reach the screed. It takes some pre-planning on a pad that size, but keeping that optical cone clear is everythign.

And check your **Search Window** settings in the Topcon controller. If the search area is set too wide, the total station will scan the whole horizon looking for that prism every time it loses lock. Narrowing that window down to just a few degrees will help it re-acquire the target much faster. Also, make sure your prism isn't picking up reflections from the pump boom itself if it's got clean chrome or mirrors, as that can confuse the tracker.

If the interference is unavoidable due to the reach, you might consider switching to a standard rotating laser for the flat sections if your Ligchine allows it. LPS is great for complex grades, but on a massive manure pad that is mostly one or two planes, a dual-slope laser is often more reliable beacuse it isn't dependent on a single point-to-point optical lock. It'll save your guys alot of hand-tooling in the long run.

I had this exact headache on a feedlot slab last fall. What fixed it for us wasn't just raising the tripod, but actualy mounting the total station on the roof of a parked job truck. The extra height and dead-steady weight of the truck meant the pump boom never clipped the signal. Also, check your vibration. If you've got it on a tripod near the pump or a running generator, that micro-shaking messes with the Topcon's lock more than you'd think. We ended up moving our base station way out to the far corner on a concrete pad we'd poured the week before. Rock solid signal after that.

Check your hydraulic gain settings on that Pro Plus. When the Topcon drops lock, the machine reacts based on its 'Lost Signal' preset. If your gain is cranked too high, it’ll jerk the head the second it loses the LPS. Dial back the valve response just a hair. Also, are you running the 360-degree prism? On a manure pad that big, ussually 6-inch thick 4,000 psi stuff, that screed is working hard. If the prism is shaking or the glass is dirty from pump splatter, you're toast. Clean the optics with some isopropyl every few trucks and see if that smooths out the re-acquisition.

This is all way over my head, but I'm trying to learn. Is a 'total station' basially just a high-tech laser level? I didn't realize concrete work involved so much computer tech. When you guys talk about the 'prism' picking up reflections, does that mean even a shiny truck parked nearby coud mess up the whole slab? I’m just curious if there’s a low-tech backup for when the sensors fail on a project this big, or do you just have to stop the whole the pour?

Quick update—mounting the total station on the truck roof worked perfectly. Getting it above the pump boom height kept the line of sight clear all afternoon. I also dialed back the hydraulic gain like suggested, wich stopped that aggressive stuttering whenever the signal flickered. The slab is looking much better now and the guys aren't fixing marks by hand anymore. Thanks for the help!