Dissolved oxygen sensors answer a difficult question: how do you measure gas in a liquid? For example, the chemical symbol for water H2O tells you that two hydrogen atoms bond with an oxygen atom to form a molecule of water. But what a dissolved oxygen sensor measures is additional oxygen in the liquid not bonded to anything else.
If you think about it, you know there is free oxygen gas in water because fish gills are designed to filter it out and breathe it. Normally, about 10 molecules of oxygen are dissolved in every million molecules of water in a healthy lake or stream. Flow the water down rocks or a waterfall and the oxygen level increases. Let the water sit stagnant or add organic bacteria that consume decaying material, the oxygen level goes down, and fish can’t breathe.
Oxygen is not only present in water, but in many other fluids. For example, oxygenated chemical compounds are added to gasoline to reduce carbon monoxide and soot during combustion.
While there are many ways to measure dissolved oxygen, one of the most accurate is fluorescent sensors. They measure the DO concentration in water based on the principal of quenching of luminescence in the presence of oxygen. A special layer of film coated with a dye is exposed to light (excited) and exposed to air or liquid with oxygen. The amount of oxygen is proportionate to the lowering (quenching) of the excited state of the dye. The more quenching recorded, the more oxygen that is present.
Although the process of quenching by luminescence has been understood for decades, improved dyes, LED light sources, photodetectors and electronics that have made the process very precise in measuring oxygen in both gas and liquid.
Optical dissolved oxygen sensors offer several advantages. They are less susceptible to light source and detector drift as well as drift due to dye degradation or leaching.
At GasLab, we offer both a handheld DO sensor as well as a permanent mount sensor designed for industrial production applications.
TecMicro DO Sensors
TecMicro Dissolved Oxygen Sensors can measure oxygen levels from a few parts per billion up to 40mg/L in liquid depending on the model. This makes them useful for fermentation, liquid packaging, breweries, wastewater, algae or aquatic applications.
Watch a video of the TecMicro DO Sensor being tested.
Advantages of the TecMicro Sensor
- Can be connected to a PLC, RPI, Arduino or any other control/monitor system
- Permanently installed process instrumentation sensor
- Liquid measurement in flow (pipeline) or static (sealed tank) conditions
- Clean in place or sterilize in place using high heat or chemicals
- Remote calibration using a control gas or liquid for automated calibration cycles
- RS485 electromagnetic immunity
- The TecMicro works under high pressure 50 Bar / 750 Psi.
- Both gas and liquid models available using the same RS485 interface
TecPen Portable DO Meter
The TecPen Portable Dissolved Oxygen Meter provides accurate O2 measurement in mg/L or parts per billion (ppb) in water and other liquids. It is useful in measuring trace oxygen levels from 0-5% for biological or industrial applications, or for quality control in packaged liquids.
The TecPen DO Meter works by utilizing a micro-pump that draws a liquid sample inside the device. Once the oxygen level has stabilized, it can be read on the screen or saved in internal memory for later downloading and data analysis.
Because of its advanced optical chemical sensor, the TecPen Portable Dissolved Oxygen Meter can take a measurement in 3 seconds. It is designed to last for years.