Although some flow is usually beneficial, excessive flow, turbulence, pressure, or mechanical vibration can create problems depending on the sensor design and installation.
One issue is streaming potential, which occurs when liquid moves across charged surfaces and generates small electrical potentials. In some installations, most noticeably in low-conductivity media, these potentials can appear as noise or unstable readings.
High flow or pressure conditions can also place more mechanical stress on the sensor, its junction, or its mounting hardware. In certain reference electrode designs, pressure differences or aggressive process conditions can also accelerate electrolyte depletion, junction instability, or contamination of the reference system. The extent of these effects depends on the sensor construction and the specific process environment.
A related effect shows up as the reference junction ages or interacts with the process. A healthy junction produces a small, stable diaphragm potential, but once it becomes fouled, coated, or chemically altered by the medium, that potential can grow and become strongly flow-dependent. Because it adds directly to the measured signal, a junction potential that shifts with flow can cause large, unstable pH swings — often a sign that the reference, not the glass, needs attention.
High flow, turbulence, or pressure drops can also entrain gas bubbles. A bubble on the glass membrane briefly interrupts the reading, but a bubble resting on the reference diaphragm is more disruptive: it breaks the electrolytic path the reference relies on, causing noise, spikes, or unstable readings. Mounting the sensor so bubbles rise away from the junction rather than collecting on it helps avoid this.
