Model 430 Dissolved Oxygen Sensor

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LARGE ELECTROLYTE RESERVOIR allows up to twelve months and often longer between refills. OPTIONAL MOUNTING BRACKET allows easy removal of the sensor from an aeration basin without the use of tools. MODULAR PRESSURE COMPENSATOR AND MEMBRANE RETAINER simplify recharging and membrane replacement. MEMBRANE RETAINER REPLACEMENT AND RECHARGING require no tools.

FEATURES AND APPLICATIONS The Rosemount Analytical Model 430 Dissolved Oxygen Sensor, used with the Model 1181 Dissolved Oxygen Analyzer, measure oxygen levels in a variety of applications. The most widely used application is the secondary phase of the waste treatment process where a critical dissolved oxygen level must be maintained for the digestive process to occur. Other applications include water quality monitoring in natural bodies of water such as rivers and streams, or any location where adequate oxygen content is important to sustain aquatic life. The Model 430 Dissolved Oxygen Sensor is constructed of PVC with an oxygen permeable membrane made with Teflon®. This membrane is held in place with a membrane retainer. OPERATION As oxygen passes through the Teflon® membrane an oxygen dependent electrochemical reaction takes place between the gold cathode and silver anode in the presence of the electrolyte. The resultant current flow between these elements is proportional to the quantity of oxygen which has entered the sensor. Temperature and pressure compensation are both standard features on the Model 430. Temperature compensation is necessary for two reasons: First, the solubility of oxygen in water decreases with an increase in temperature; secondly, the permeability of the Teflon® membrane and the oxygen diffusion rate increase as the temperature increases. For these reasons, it is important for a dissolved oxygen measurement to be accompanied by an accurate temperature measurement. Temperature compensation is accomplished by means of a thermistor located in the sensor housing, and its associated circuitry in the analyzer. Pressure compensation is a mechanical rather than electronic correction. It is important for the tension on the Teflon® membrane to remain constant at all times, even with sample pressure changes. Fluctuations in membrane tension affect its diffusion characteristics. By means of a pressure compensator the pressure on the sample side of the compensator membrane is transmitted to the electrolyte reservoir so the pressure on both sides of the membrane remains equal. In this manner, sample pressure changes do not affect the diffusion rate of oxygen through the membrane. The Teflon® membrane is held in place by a retainer. A water-tight seal is made with an O-ring between the membrane and sensor reservoir. Membrane replacement is rarely required, but in those situations when it is necessary, the procedure can be performed quickly and easily. Since oxygen diffuses through the Teflon® membrane at a faster rate than through the sample, it is necessary to continuously maintain a fresh sample in front of the membrane. A stream velocity of approximately 1.5 feet per second (0.5 m/s) is required to ensure that a fresh sample is in contact with the membrane at all times. Teflon® is a registered trademark of DuPont Films.