Using Integral Cable Sensors in Underwater Applications
Underwater applications for vibration sensors can be problematic at times. As the sensors require some type of power, the possibility of water ingression into either the sensor or cable makes failure a frequent possibility, especially in applications where water turbulence or inclusions may be an issue. With that in mind, proper preparations can greatly increase the chances of successfully installing sensors for long-term monitoring of pumps and other underwater machinery.
Integral Cable Sensor Selection
Selecting the proper sensor for the application is the first step. Many articles have been written on choosing the right sensor for machinery based on operating speed and other factors, but what we are concerned with here is the physical properties of the installation site. Key factors to consider are:
- Liquid that the sensor will be immersed in
- Possible “inclusions” in the submersing liquid
- Depth of submersion
For clean freshwater submersion, the primary cable choice will be the integral polyurethane jacketed cable. For seawater, armored FEP-jacketed cable is preferred as polyurethane can deteriorate over time in seawater. Integral armor may also be preferred should there be “inclusions,” such as may be found in wastewater treatment plants, natural freshwater lakes, rivers, and streams.
Integral Cable Sensor Installation
The next most important factor to be considered is the sensor installation. While epoxy or magnet mounting may be useful in rare situations, either method can allow the sensor to become dislodged over time. The best method for installation is mounting the sensor in a hole that has been drilled and tapped in one of the machine bearings or flanges. Cables should be carefully routed and protected for the run out or up to the point where they can be terminated in a junction box of some sort.
