Stalker: Call of Pripyat → Quests → Tempting Business
Either way, once you’ve collected the detectors, take them to the scientists, and then head back to Zaton. You’ll have a bit of trouble with Sych—he’ll refuse to share the kharab with the stalkers, hinting at a certain Sultan. We can intimidate Sych and help Boroda, or we can try to respect the local gangster boss. Either way, we’ll get our next mission…
After you clear the mercenary camp, Sych will task you with finding three Veles detectors and bringing them to the scientists’ base (outskirts of Jupiter). You’ll definitely get one for clearing the bloodsucker lair at Zaton. The other can be found in Kopachi, in an excavator.
Another one can be purchased. And another one can be obtained by completing the scientists’ quest line.
See also:
How to survive a solar eclipse