Choose the Right Sensor for Water Quality Monitoring
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Sensors are the backbone of any water quality monitoring system since they determine accuracy and reliability. As such, it is best to start with picking the sensor(s) when designing a new system for applications such as pollution control, saltwater ingression studies, aquaculture, process control, etc.
There are many factors to consider when deciding what sensor is right for your application. Obviously, the most important aspects are whether the physical demands of your application are within the limitations of the sensor, but there are many other considerations that come into play. For instance;
Stability is important to consider because a sensor that requires calibration every week does not work for an application where an operator only visits the site every month. Some sensors, such as those that measure conductivity, require calibration much less frequently than pH or ORP sensors, simply due to the nature of the sensor. As such, it is important to research electrode design to understand what unique features are beneficial.
The next important considerations to verify that the sensor works for your application are the physical limitations, as outlined above. Size does matter, at least when installing sensors into pre-existing systems such as wells or boreholes that may prevent the use of sensors larger than a certain diameter. It also may be cost-prohibitive to use large diameter sensors in new projects such as groundwater monitoring, as drilling a wider hole can exponentially increase costs.
Each type of signal has its pros and cons. For example, serial communication protocols like SDI-12 and RS-485 allow for multiple sensors to be connected in series, reducing the number of receivers necessary for large numbers of sensors in a small area. In contrast, 4-20 mA sensors require individual I/O ports for each sensor and can only transmit an analog signal that must be scaled by the receiver. Because of these differences, there is no single best signal for all applications, so it is important to understand the pros and cons of each type.
What factors a sensor compensates for, along with the customizability of them, are also important to consider. For example, conductivity temperature compensation can vary significantly depending on whether a sample is high or low conductivity, typically ranging from 1.8-4% respectively. Using a sensor with variable temperature compensation allows for more precise measurements across a wide range of samples.
Other features that affect measurement accuracy include isolation and a solution-ground, both of which mitigate background noise. Due to the sensitivity of water quality sensors, small amounts of electromagnetic interference can lead to inaccurate results.
Ease-of-use is also important because a sensor is worthless if it is too time-consuming to set up and maintain. Digital sensors benefit from the ability to store calibration information and perform complex calculations but must have a good user interface to do so while also providing easy installation. Analog sensors, on the other hand, are generally easier to set up, maintain, and troubleshoot but may not have as many features.
Read the full guide on what to consider when selecting a water quality sensor on pHionics website here >>