Measuring isopropyl alcohol levels in confined ATEX zones

An automated machine dipping a rubber seal into isopropyl alcohol every 15 seconds needed the IPA level held within plus or minus 1mm inside a small cylindrical cup mounted in an ATEX-classified zone, since IPA is flammable. Too low a level and the seal misses full coverage; too high and the coating goes inconsistent. Complicating things further, a cycling lid opened for roughly one second between each 14-second dip, creating pressure transients in the headspace that would corrupt a single-port pressure reading. Ultrasonic and float-based level sensors were ruled out, leaving differential pressure level measurement as the practical route: calculating liquid level from the pressure difference between the bottom of the vessel and the space above the liquid, using externally mounted, ATEX-certified sensors that don't need internal space in an already mechanically constrained cup.