Monitoring OFF-LINE is basically realized by trend analysis.
The following measurements are analyzed while trending:
- measurement of vibration values: displacement, velocity, acceleration, depending on
- machine type or customer requirements),
- measurement of bearing condition by SPM method,
- measurement of pump cavitation
Measurement results and analysis of trend curves changes, are used to estimate the machine condition as " good or requiring correction".
Classification of machine condition is proceeded in accordance with PN, VDI, ISO or manuals provided by customer.
In case machine requires correction, then analysis helps to find the reason of machine defects and to proceed with corrections, if customer requires.
For critical machines we suggest monitoring OFF-LINE at the level of trend analy
Measurements are extended by following elements:
- Spectrum analysis of vibration velocity,
- Enveloped spectrum analysis of bearings.
Measurements of that kind, enable early detection of damage and determination of their reasons, when failure do not yet cause the vibration values increase.
Preparation for measurement
In order to proceed with monitoring OFF-LINE in efficient and proper way, some preparation works must be carried out before, which are machine technical analysis, preparing of data base and adopting machines for measurements, see below for more details:
- Analysis of machines to be measured, basing on list of machines received from customer. Division of machines into groups depending on type and importance. Determination of frequency of measurements for each group.
- Preparing of technical characteristics basing on documentation and inspection on site. For each machine type following characteristics must be determined: measuring points, measurement scope (bearing vibration measurement, bearing condition parameters, cavitation, RPM, temperature) and threshold values qualifying machine technical condition.
- Preparing the site map of machines and measuring points. Determining of measurement routes.
- Creating of data base including map of machines and measuring points and also technical characteristics like: RPM, catalog no. of bearing, number of gear teeth , number of blades etc.)
- Preparing of machines
Preparing of machine mainly consists in providing of suitable conditions of measurements in order to get reliable and repeatable results and analysis.
PRÜFTECHNIK developed VIBCODE system - coded measurement locations. The probe locks onto the measurement stud via bayonet mount and reads its encoded plastic ring. Then it reads the machine signals programmed for that location. VIBCODE therefore delivers extremely reliable trending results by ensuring that the location, measurement direction and probe pressure are exactly the same each time.
Each measurement is realized according to following schedule:
- Measurement of machine parameters basing on prepared measurement routes, with using the data collector and machine analyzer.
- Analysis of trend curves and changes in measured values. Specifying of machines and points to be measured.
- Diagnostics of machine conditions in determined points, consists of following elements:
- order analysis,
- spectrum analysis,
- enveloped spectrum analysis,
- Analysis of results from measurements. Assessment of machine condition, determining of reasons of failure and suggested corrections. Report from measurement.
Corrections are performed as a result of monitoring and it's determined as "requiring correction") or on customer request when he noticed that machine condition got worse.
Before entering to correcting services, in order to specify the exact reasons of failure, the measurement in extended scope should be performed together with additional measurements such as control of shaft curvature and rotor run-out, control of clearance, tension of covers and expansion gap of bearings, coupling laser alignment etc.). The scope of measurement depends on need.
The scope of corrections is established basing on measuring results and as agreed with customer, it might consists of following elements:
- Correction of bearing cover tension
- Coupling alignment
- Replacement of bearings
- New rotors assembly
Each measurement and correction is followed by report containing all measurement results and analysis, description of corrections carried out together with final results, effects, and finally estimation of machine condition and conclusions, recommendations.
The cost of monitoring off-line depends on number of machines to be measured and frequency of measurement.