The Electrolytic sensor uses two closely spaced, parallel windings coated with a thin film of phosphorus pentoxide (P2O5). As this coating absorbs incoming water vapor, an electrical potential is applied to the windings that electrolyzes the water to hydrogen and oxygen. The current consumed by the electrolysis determines the mass of water vapor entering the sensor. The flow rate and pressure of the incoming sample must be controlled precisely to maintain a standard sample mass flow rate into the sensor.
The method is fairly inexpensive and can be used effectively in pure gas streams where response rates are not critical. Contamination from oils, liquids or glycols on the windings will cause drift in the readings and damage to the sensor. The sensor cannot react to sudden changes in moisture, i.e., the reaction on the windings’ surfaces takes some time to stabilize. Large amounts of water in the pipeline (called slugs) will wet the surface and requires tens of minutes or hours to “dry-down.” Effective sample conditioning and removal of liquids is essential when using this sensor.