As its name suggests Operational Deflection Shape analysis shows the vibration pattern experienced during normal operational condition. This is different to other structural vibration tests such as impact hammer tests, bump tests or shaker tests which require a more controlled excitation force and are used to determine specific characteristics of the structure under test, such as natural or resonant frequencies.
Have you ever wondered if there is a vibration condition monitoring system that can be installed anywhere and then monitored from anywhere else? Even on your smartphone? Well, there is. The following…
A vibration problem arose at an Open Cycle Gas Turbine. Following an outage on the four gas turbines and two SSS[1] clutches, the machine returned to service with unacceptable vibration…
The use of a vibration condition monitoring system for monitoring vibration from large rotating machines fitted with fluid-filled journal bearings such as steam or gas turbines is well understood. Vibration from these components generally falls within the main harmonics or orders of the shaft rotational speed such as 1st, 2nd 3rd or 4th harmonic. Some energy may also exist below the 1st order, called the sub-synchronous component. Most energy exists below 1KHz and so standard displacement probes or velocity transducers are generally fitted. The Prosig PROTOR system collects this data in amplitude and phase form, relative to a ‘once-per-revolution’ phase reference signal, as standard and allows data to be displayed in real-time as mimic diagrams, trend plots, orbit and vector displays.
Ever been lying on the beach and begun to wonder about the state of your LP turbines? Or out on business and anxious to know if that troublesome exciter bearing has settled down? Well with a Prosig PROTOR system and a smartphone anything’s possible. Many of you will be familiar with using your phone as a camera, music player, web browser, email client, calculator or even a navigation device, but not many will have anticipated using it for vibration condition monitoring!
Here we will explain how to use one of the new Android based phones to connect to a PROTOR system. For the purposes of this example we used an Android-based phone and a WiFi connection. It is equally acceptable to use the network providers 2G/3G data connection. And although we chose an Android based phone, similar VNC-viewer apps exist for the iPhone and other smartphones.
Shaft displacement is an important vibration measurement for rotating machines. Shaft displacement is usually monitored by non-contact shaft displacement probes such as eddy-current probes. These probes produce a voltage proportional to the distance of the shaft surface relative to the tip of the probe. For maximum benefit, ideally two shaft displacement probes will be fitted to measure the displacement in both the horizontal and vertical directions. Actually the probes do not have to be exactly horizontal and vertical as Prosig’s PROTOR system is able to resolve into the horizontal and vertical directions.
Any vibration signal may be analyzed into amplitude and phase as a function of frequency. The phase represents fifty percent of the information so it is most important to measure phase for vibration monitoring. Most vibrations on a rotating machine are related to the rotational speed so it is clearly important to have a measure of the speed, either directly or as a once per revolution tacho pulse. A question sometimes arises as to whether a once per revolution tacho reference signal is needed to measure phase. Is it possible to get phase if we only have a speed signal? This note gives some insight into those questions.
Actually the question that should be asked is – “Can we measure a meaningful phase, for use in vibration monitoring, if we only have a speed signal as well as the vibration signals?”
Prosig installed a PROTOR system at the Ringhals1 reactor in Sweden in 1992. This system was based on the PROTOR2 level of hardware and software and consisted of a Sun workstation and PC based acquisition system. The system has been successfully monitoring the two main turbine generators ever since. Last month Prosig upgraded this system to their latest PROTOR4 hardware and software.
The system now consists of a high-end rack-mount server PC containing RAID, hot-swap disks, dual high-speed Ethernet LANs and redundant power supplies together with two 32-channel 4700 data acquisition units.
The system is connected into the station alarm system so that control room staff are automatically alerted on vibration alarms. The system is fully integrated within the Ringhals network for data archiving, remote access and data transfer with the plant computer.
