Reducing the Effects of EMI
The best way to prevent electromagnetic induction from affecting water quality (or any) measurement is with proper planning. For applications such as process control or wastewater monitoring, where strong motors and solenoid pumps are nearby and required for the application, it is extremely important to place any measurement devices away from heavy machinery. This also includes the cables running from the measurement devices as, even with shielding, transmission is susceptible to noise and EM induction can be very powerful. If facilities are not designed with EMI in mind, then they face expensive restructuring when accurate measurements—and therefore quality control of production—are not possible.
Regarding water quality monitoring for environmental remediation or other purposes, electromagnetic induction is still a risk in areas of human activity. For any study, pay attention to common travel routes for boats to avoid induction from their engines and place measurement devices away from dock powerlines. Methods to reduce the effects of EM induction are provided later in the article
Electromagnetic Radiation Prevention
Again, planning is important, especially as manufacturing facilities move toward the dense communication structure required for 5G. Ensure there is a place to install the sensor away from routers or other sources of wireless communication. Due to the long-range transmission capabilities of these wireless signals, there can still be interference even when sensors are not installed close to a source, which is why we have included other methods of EMI reduction below.
Use Quality Cables
For any application requiring high accuracy, a shielded, twisted pair (STP) cable should be used.
Twisted pair wires are two conductors from one circuit that twist around each other. The twisting ensures that both wires are, on average, equidistant from any source of EMI, making any noise common across both conductors. The common-mode noise can then be removed more easily by the receiver using various methods.
Shielded cables have a wire that connects to either a foil or braided shield which passes electricity through it to form a Faraday Cage around the inner twisted pair wires, thereby reducing the effect of EMI. A helpful demonstration of the effectiveness of a Faraday Cage has been posted by MIT.
Proper Cable Routing
Always distance power cables away from signal cables to prevent EMI. Separation distances are outside the scope of this article, but Electrical Engineering Portal has effectively summarized the guidelines.
As most measurement signals are low power (e.g. pH and ORP measured in mV), one of the most effective means of reducing EMI is to strengthen, or amplify, the signal before transmission from the sensor to transmitter/receiver. This ensures that any interference is a smaller percentage of the total output, increasing the signal-to-noise ratio. Signal amplification works well assuming any point of interference is after the sensor. Products will generally advertise whether they have this feature built-in, sometimes referred to as a “preamp”. It is possible to add aftermarket signal amplification onto a product, but this method would not be as effective if any length of cable between the sensor and preamp is exposed to EMI.