Oil and grease can cause interference with which sensor?

• A. pH meter
• B. Conductivity meter
• C. Flow sensor
• D. ORP probe

Answer: (D)

Oil and grease form a film on sensor surfaces, blocking contact between the electrode and the sample. ORP probes measure the redox potential at the electrode surface, so a greasy film hinders electron transfer and can shift or drift the reading, sometimes introducing oil-related redox-active species that bias the result. That direct interference with the surface chemistry makes the ORP measurement the most affected.

pH meters rely on hydrogen ion activity at a glass membrane, which can be slowed or fouled by contaminants but isn’t driven by surface redox reactions. Conductivity meters depend on ion movement between electrodes; an oil film can insulate and reduce contact, but the problem is less about redox chemistry and more about ion access. Flow sensors are typically mechanical, so they’re less impacted by oil in terms of the measurement principle itself.