By Don Davies, Technical Director, Prosig
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 PROTOR (http://www.prosig.com/protor) is able to resolve into the horizontal and vertical directions.
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By Dr Colin Mercer, Technical Director, Prosig
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 some time 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?” read »»»
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.
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