Vibration monitoring package is ideal solution for cooling tower fans
5 December 2025 
Effective monitoring of critical infrastructure is an essential requirement across the power generation, oil, gas and petrochemical industries, where smooth running and trouble-free system operation are vital – especially in today’s highly competitive and energy cost-conscious environment.
Condition monitoring specialist Sensonics is an expert in developing highly effective monitoring systems, with over 50 years of experience that includes vibration monitoring products. A good example of this is the recent completion of a cooling tower monitoring project at a major petrochemicals plant.
The Project Engineer at the site confirmed that they were seeking a suitable system to monitor and protect cooling tower fans, in order to prevent issues in the event of fan blade failure. The requirement was for individual systems to monitor each of the twenty motor/gearbox-driven fans, which were located between the motors and the fans around the base of the cooling tower.
Confirming the specific requirements of the application, the Project Engineer commented: “The fan speed is 131 RPM (2.18 Hz), and what we want is to have a single transducer mounted on the gearbox (each fan is mounted on the gearbox output shaft). The issue we want to address is the potential failure of the fan blades. When this has happened, the vibration has been so severe it has damaged the concrete platform on which the fan assembly is mounted, as well as damaging adjacent fans due to fan projectiles.”
It was also confirmed that: “The atmosphere where the fan is mounted is very wet and windy, as the fans pull moist air out of the cooling tower packing and blow it across the gearbox and motor.”
Confirmation of these specific issues and challenges initially suggested the need to install a suitably ranged 4–20 mA vibration transducer, and then feed this to a nearby control unit containing the start/stop buttons for the fans. This would enable the tripping of a fan if the vibration became excessive.
There was also a requirement to feed the overall vibration levels to the main plant DCS system. Due to the specific nature of this application, the frequency response of the transducers needed to be below 2 Hz. There was no requirement for any local display or further diagnostics — just a simple system that would reliably trip the fan if it was failing, while providing an indication of the overall vibration level on the DCS.
Once the specific requirements of this vibration monitoring application were confirmed, Sensonics was able to recommend and supply a combination of its DN26 G3 dual-channel protection system along with its VEL/GLF low-frequency (slow-speed) velocity transducers.
Established in the condition monitoring market for many years, Sensonics has supplied thousands of these compact and innovative DIN rail-mountable DN26 G3 dual-channel vibration monitors, which have delivered reliable and cost-effective vibration monitoring across a wide range of installations. This high-performance, fully programmable signal conditioning unit is capable of monitoring two channels of absolute vibration, shaft vibration or shaft position, while a third channel option is available for measuring speed or for use as a phase reference.
To complete the solution for this application, Sensonics’ VEL/GLF low-frequency velocity transducer proved to be ideally suited to the large fans operating at a low RPM. This electrodynamic sensor provides superior performance compared to piezoelectric devices by combining high measurement sensitivity with a frequency response down to 0.5 Hz.
This level of sensitivity, along with excellent noise performance, provides the necessary dynamic range required for detailed analysis of gearbox vibration, making it ideal for measuring velocity vibration on equipment operating at speeds down to 30 RPM. Furthermore, the VEL/GLF offers advantages over traditional piezoelectric-based velocity vibration sensors, which can be susceptible to various forms of interference in low-frequency applications, potentially resulting in spurious readings and alarms.
As a result of its robust design, the VEL/GLF offers high noise immunity due to the low-impedance electrodynamic nature of the sensor assembly. In addition, the filtering of high-frequency events — and the fact that no electronic integration is required — means that the design of the sensor is immune to the saturation problems that can impair the reliability of other piezoelectric devices.
For further information please visit:
https://www.sensonics.co.uk/vibration-position-monitoring