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Dissolved oxygen meters consist of a sensor, a connecting line, and meter for calculating and displaying measurements. The sensor will be one of the types described in the How Dissolved Oxygen Meters Work section. The measurements taken by the sensor are sent up a cable and computed in the meter itself. The information is then displayed on a screen. Some models will automatically calibrate and others have controls for manual calibration.
How dissolved oxygen meters work
There are two types of sensors available on dissolved oxygen meters, optical and electrochemical. Optical sensors measure the interaction between oxygen and luminescent dyes. The sensor is lowered into the water and water is allowed across a semi-permeable membrane to enter a chamber containing the dye, sensing element, light-emitting diode, and a photo detector. Blue light excites the dye, electrons gain energy, and light is emitted as the electrons move back out of the light and return to their natural state. Some optical sensors also have a red light as a reference as red light does not excited the electrons. A measurement of the energy of the electrons is used to calculate the amount of oxygen dissolved in the water.
There are 3 types of electrochemical dissolved oxygen sensors, steady polargraphic, pulsed polargraphic, and galvanic. All 3 types consist of the same features: 2 polarized electrodes, an anode and cathode in an electrolyte solution. Water diffuses across a membrane, the dissolved oxygen is consumed at the cathode, and electrical current is created and carried by ions to the anode. One difference between the 3 types of electrochemical sensors is the polarization of the electrodes. The polargraphic sensors take some time to warm up and polarize the electrodes. Galvanic sensors have electrodes made of dissimilar metals allowing for immediate self-polarization and no warm up time. Steady polargraphic sensors take constant readings while pulsed polargraphic sensors take readings in short intervals, which allows the concentration of dissolved oxygen to replenish across the membrane.
About dissolved oxygen meters
Dissolved oxygen meters measure the amount of oxygen in water. Measuring oxygen dissolved in water is crucial to the aquatic animals and plant life that live in it. You may have other reasons to measure dissolved oxygen. The amount of oxygen in water is dependant on the pressure and temperature of the water.