Posted to News on 1st Mar 2021, 08:55
Good vibrations for low-speed rotating machinery
Effective monitoring of slow-speed rotating industrial applications, such as wind power generation and hydro-electric turbines, is critical
Wind power and hydro-electric considerations aside, similar levels of monitoring are essential on standard-speed applications, advises condition monitoring specialist Sensonics, especially given the increasing importance of ‘green-energy’ alternatives.
Reliable and effective vibration measurement of low-speed machinery (typically less than 300 rpm) helps to ensure that machinery and plant are functioning at optimal levels. This is one of the areas in which Sensonics provides solutions. “In all situations, the focus should be: understand the dynamic behaviour, establish a baseline vibration performance and then detect the early onset of failure in rotating parts,” advises the company, “which, if left unchecked, has the potential to result in more serious damage, affecting overall performance.”
Low frequency velocity vibration sensor
While using accelerometers is commonplace on standard speed machinery (usually 1,500 rpm), this becomes problematic at lower speeds, as the absolute accelerations measured are much smaller in value for similar vibration displacements. In recognition of the need for a sensor to meet these specific requirements, says Sensonics, it developed its low frequency velocity vibration sensor, the VEL/GLF.
“The VEL/GLF is an electro dynamic sensor, which has become established as the preferred option for measuring vibration on slow speed rotating machinery,” the company states. “It offers a superior performance compared to piezo-electric devices by combining high measurement sensitivity with a frequency response down to 0.5 Hz, making it ideally suited to measuring velocity vibration on equipment with speeds below 300 rpm.”
Readings and alarms
The sensor offers a standard IEPE type interface to enable easy integration with existing plant protection and monitoring equipment. “Furthermore, the VEL/GLF provides advantages over traditional piezoelectric-based velocity vibration sensors, which are susceptible to many forms of interference in low frequency applications that can result in spurious readings and alarms.”
According to Sensonics, typical causes of these unwanted readings and alarms include: base strain effects, due to temperature changes amplified through the internal signal processing; high frequency; and high g vibration events caused by auxiliary machine items, resulting in transducer saturation. Also, mains voltage interference, due to a combination of a poor local plant earth and insufficient transducer internal isolation.
High noise immunity
“Thanks to its robust design, the VEL/GLF combats these effects, offering high noise immunity, due to the low impedance electro dynamic nature of the sensor assembly. In addition to the filtering of high frequency events and since no electronic integration is required, the design is immune to the saturation problems that impair the reliability of piezoelectric devices.”
Typical applications for the VEL/GLF will be found in wind power generation, hydro-electric plants and cooling towers, on slow speed pumps and also structural monitoring.
