Why techniques differ
Equipment fails in different ways, and each way leaves a different trace. A worn bearing makes vibration. A contaminated lubricant carries wear particles. A loose electrical connection runs hot. A compressed air leak hisses at frequencies the ear cannot easily hear. Condition monitoring techniques are simply different ways of picking up those traces. Choosing among them is a matter of matching the method to the failure you expect.
Vibration monitoring
Vibration is the workhorse for rotating machinery such as motors, pumps, fans and gearboxes. A sensor, typically an accelerometer, measures how the machine shakes. Overall levels rising over time suggest something is changing. A closer frequency-based look can point to the likely source, since imbalance, misalignment, looseness and bearing defects each tend to show characteristic patterns. The interpretation of those patterns is a skill in its own right; vibration analysis is usually done or reviewed by trained analysts.
Detects: imbalance, shaft misalignment, looseness, bearing and gear defects, some resonance problems. Limits: needs a sensor placed well on a rigid part of the machine; slow-moving or very irregular machinery is harder to assess; results require interpretation.
Oil analysis
Samples of lubricating or hydraulic oil are tested for condition and contamination. Tests commonly look at viscosity, water content, additive state and the presence and type of particles. Metals in the oil can hint at which internal parts are wearing, while particles such as dirt point to ingress through seals or breathers.
Detects: lubricant breakdown, contamination, abnormal wear in gearboxes, hydraulic systems and engines. Limits: results depend on taking representative samples in a consistent way; lab turnaround can delay answers; it applies only to oil-lubricated equipment. Good sampling habits matter as much as the lab.
Thermography
Infrared cameras show surface temperature as an image. Hot spots can reveal loose or corroded electrical connections, overloaded circuits, failing bearings, blocked flow in heat exchangers or missing insulation. Because the camera is handheld and non-contact, surveys can be done on live equipment from a safe distance, within the plant’s rules for the area.
Detects: electrical hot spots, overheating mechanical components, thermal patterns in process equipment. Limits: it sees surfaces, not the interior; shiny surfaces and reflections can mislead; a good reading needs the equipment to be under load; interpretation needs experience. Electrical enclosures should only be opened by qualified personnel following safe work procedures.
Ultrasound
Airborne and structure-borne ultrasound methods pick up high-frequency sound produced by friction, turbulence and electrical discharge. In practice they are used to locate compressed air and gas leaks, to listen for early bearing distress, to check whether steam traps are passing properly, and to detect some electrical discharge activity.
Detects: leaks, early bearing friction, steam trap faults, certain electrical issues. Limits: background noise can interfere; the technique is mostly handheld and periodic; interpretation depends on the operator’s skill.
Motor current and electrical testing
Looking at the electrical supply to a motor can reveal issues that vibration might not. Changes in current patterns may indicate rotor problems, some supply imbalance, or mechanical load changes in the driven equipment. More detailed electrical tests are available with the motor offline. These methods can be useful when a motor is hard to reach for sensors.
Detects: certain motor and supply problems, load variations. Limits: needs specialized equipment and analysis; less direct for diagnosing mechanical faults.
Simple but valuable: process and performance data
Not all useful signals need special instruments. Existing readings of pressure, flow and temperature show when a pump or compressor is operating off its normal curve. A pump delivering less flow than before for the same power draw may have worn internals or be suffering from pump cavitation. Operators’ observations of noise, smell and leaks also count as condition data.
Comparing techniques at a glance
| Technique | Typically strong for | Typically weaker for |
|---|---|---|
| Vibration | Rotating mechanical faults | Non-rotating items, interpretation effort |
| Oil analysis | Lubricant health, internal wear | Equipment without oil systems |
| Thermography | Electrical hot spots, overheating | Internal faults, reflective surfaces |
| Ultrasound | Leaks, early friction | Noisy environments |
| Motor current | Motor and load changes | Pinpointing mechanical causes |
Combining methods
No single method covers everything, and combining two or three often gives better confidence. For example, rising bearing vibration confirmed by a temperature increase and metal particles in the oil makes a stronger case for intervention than any one sign alone. Likewise, a thermal survey might flag a hot connection that no vibration sensor would ever notice.
When deciding which to adopt, consider the machine’s failure modes, its importance, how often it needs checking, and what skills the plant has or can buy in. Periodic route-based surveys suit many assets; continuous sensors are more often reserved for critical or hard-to-reach equipment. Either way, a detection is only the start: the team still needs to inspect, plan the repair and record the outcome.