Understanding Online Monitoring
Definition: What is Online Monitoring?
Online monitoring (also called permanent monitoring, continuous monitoring, or installed systems) is a condition monitoring approach using permanently installed sensors and instruments that automatically collect vibration, temperature, and other data continuously or at frequent intervals (every few seconds to hours) without human intervention. Unlike route-based monitoring where technicians periodically visit equipment, online systems provide 24/7 surveillance, real-time alarming, and automatic data trending for critical machinery.
Online monitoring is essential for high-value or critical equipment where early fault detection, immediate alarming, and protection from catastrophic failure justify the higher investment in permanent sensors and monitoring infrastructure. It represents the premium tier of condition monitoring, providing maximum protection and data richness.
System Components
Permanently Installed Sensors
- Accelerometers at each bearing (2-3 per bearing typical)
- Proximity probes for shaft displacement (XY pairs)
- Temperature sensors (RTDs or thermocouples)
- Tachometer or keyphasor for speed/phase
- All cabled to central monitoring hardware
Monitoring Hardware
- Multi-channel data acquisition system
- Signal conditioning and processing
- Network connectivity
- Local processing and alarming
- Rack-mounted in control room or equipment area
Software and Networking
- Real-time display and trending
- Automatic alarm management
- Data historian and archiving
- Network integration with plant systems
- Remote access capabilities
Advantages
Immediate Fault Detection
- Detects problems as they develop (not waiting for next route visit)
- Minimum time from fault onset to detection
- Catches rapid deterioration
- Maximum lead time for corrective action
Continuous Protection
- 24/7 monitoring
- Automatic shutdown on critical vibration
- Prevents catastrophic damage
- Protects personnel and adjacent equipment
Rich Data
- High-frequency measurements (every few seconds)
- Captures transient events
- Detailed fault progression history
- Enables sophisticated analysis
Operational Benefits
- No manual data collection required
- Consistent measurement conditions
- Trending without human intervention
- Automated reporting
When to Use Online Monitoring
Critical Equipment
- Failure causes production loss > $10,000/hour
- Safety-critical (turbines, compressors)
- Environmental risk (toxic, flammable processes)
- Single point of failure (no backup)
High-Value Assets
- Equipment value > $500,000
- Replacement cost or lead time prohibitive
- Repair costs very high
- Monitoring investment small compared to asset value
Inaccessible or Hazardous
- Difficult or dangerous for routine access
- Remote locations
- Continuous process areas
- Automated facilities
Regulatory Requirements
- API 670 for turbomachinery
- Nuclear regulations
- Industry-specific mandates
Implementation Considerations
Cost
- Sensors: $500-2000 each
- Hardware: $5,000-50,000+ depending on channels
- Software: $5,000-100,000+ depending on capabilities
- Installation: wiring, commissioning
- Typical: $10,000-100,000 per machine
Integration
- DCS/PLC integration for shutdown
- CMMS linkage for work orders
- Network infrastructure
- Cybersecurity considerations
Maintenance
- System itself requires maintenance
- Sensor calibration
- Software updates
- Spare parts for monitoring system
Technologies and Features
Measurement Modes
- Continuous: Real-time signal processing
- Snapshot: Periodic detailed measurements (every few minutes)
- Alarm-Triggered: Detailed capture when alarm occurs
- Transient Capture: Startup/shutdown special recordings
Analysis Capabilities
- Overall vibration levels and trending
- FFT spectral analysis
- Envelope analysis for bearings
- Orbit analysis (with proximity probes)
- Automated fault detection algorithms
Alarming
- Multi-level alarms (alert, alarm, danger, trip)
- Email/SMS notifications
- Automatic shutdown capability
- Alarm acknowledgment and logging
ROI and Justification
Typical Payback
- Prevention of one catastrophic failure often pays for system
- Typical ROI: 2-5 years for critical equipment
- Some facilities achieve payback in < 1 year
- Ongoing benefits after initial payback
Value Drivers
- Prevented catastrophic failures
- Eliminated unplanned downtime
- Optimized maintenance (based on actual need)
- Extended equipment life (timely interventions)
- Reduced spare parts inventory
Online monitoring represents the highest tier of condition monitoring, providing continuous surveillance and immediate protection for critical machinery. While requiring significant investment, online systems deliver maximum reliability, earliest fault detection, and comprehensive data that justify costs for high-value equipment where failures have severe consequences. They are the foundation of predictive maintenance for critical assets in modern industry.
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