DVA Industrial Solutions Inc. uses modal and ODS analysis to answer a question standard vibration readings cannot: is the problem inside the machine, or is it the structure underneath it? Rotating equipment diagnostics typically focus on bearings, shafts, and couplings. But a surprising number of persistent vibration complaints trace back to how a baseplate, frame, or foundation responds to the forces a machine generates. This article explains what modal and ODS analysis measure, when each technique applies, and how the results change a repair plan.
What Modal and ODS Analysis Actually Measure
Operating Deflection Shape analysis, usually shortened to ODS, shows how a structure physically deforms while a machine runs under real operating conditions. It captures the combined response to every force acting on the structure at once. That includes both resonance and forced vibration from the rotating equipment itself.
Modal analysis takes a narrower view. Rather than watching the structure under normal operation, it identifies the natural, or resonant, frequencies of the structure itself. This happens independent of whatever machine sits on it. A known force is applied and the structural response is measured at many points. The measurements are then processed to reveal the modal parameters that describe how the structure wants to move.
Why Modal and ODS Analysis Matter for Rotating Equipment
Conventional vibration analysis at the bearing housing is excellent at catching imbalance, misalignment, and bearing wear. It is far less useful when the vibration problem originates in the supporting structure. A baseplate that flexes, a pipe rack that resonates, or a mezzanine floor that amplifies a specific frequency can all produce symptoms that look like a machine fault. They are not.
Modal and ODS analysis separate these two possibilities. If a structure’s natural frequency sits close to a machine’s operating speed, even a well-balanced, well-aligned rotor can produce high vibration readings. The structure is simply amplifying a small input into a large response.
This distinction matters for troubleshooting timelines as much as for engineering accuracy. Chasing a rotor-side repair on a machine that is actually fine wastes maintenance hours. It can also leave the real structural condition unaddressed. The same vibration complaint often returns after the next rebuild.
Common Structural Vibration Findings
Our field experience across Alberta industrial sites points to a handful of recurring findings, once a structure is actually tested rather than assumed to be rigid.
- Baseplates that were never fully grouted, leaving an air gap that flexes under load
- Piping runs that resonate at pump or compressor operating speeds
- Skid-mounted equipment where the skid itself has a low natural frequency
- Mezzanine or platform structures that amplify vibration transmitted from nearby machines
- Foundation cracking or deterioration that changes stiffness over time
Industry estimates suggest that a meaningful share of vibration complaints labeled "unsolvable," after bearing-level monitoring alone, eventually trace back to one of these structural conditions.
Comparing Modal Analysis and ODS Analysis
| Technique | What It Measures | Best Used For |
|---|---|---|
| ODS Analysis | Structural deformation under real operating forces | Diagnosing vibration while equipment runs normally |
| Modal Analysis | Natural or resonant frequencies of the structure | Confirming resonance risk before or after a modification |
| Combined Approach | Both operating response and inherent structural behavior | Complex cases involving multiple forcing frequencies |
Choosing between the two often depends on the question being asked. If the goal is to see what happens during normal operation, ODS analysis is the right starting point. If the goal is to confirm whether a structure could resonate at a proposed new speed, modal analysis with a controlled excitation gives a clearer answer.
How the Assessment Is Performed
Our analysts mount accelerometers at multiple points across the structure of interest. This covers everything from the equipment baseplate to the surrounding frame or piping. For ODS work, data is collected while the machine runs under its normal load. For modal testing, a calibrated impact or shaker provides a known excitation force, and the response is measured at each point.
The resulting data set is processed into an animated deflection model. It shows, frame by frame, how the structure moves. This visual output is far easier to explain to plant engineers than a spectrum plot alone. The animation shows exactly where the structure is flexing, and by how much.
Measurement point selection matters as much as the equipment used. Our analysts walk the structure beforehand to identify likely flex points, joints, and connections. Sensors are then placed to capture the full picture, rather than a handful of convenient locations. This planning step often determines whether the resulting animation clearly shows the root cause.
From Diagnosis to Corrective Action
Once a structural contributor is confirmed, the corrective path usually differs from a typical rotor-focused repair. Options range from adding stiffening gussets, to regrouting a baseplate, to modifying a support bracket. In some cases, the fix is adjusting the machine’s operating speed to move away from a resonant frequency. Our rotating equipment vibration analysis service is often run alongside modal and ODS work. That way both the machine and its supporting structure get evaluated together.
For facilities planning equipment upgrades or speed changes, structural verification through calibrated measurement equipment matters. Guidance from the National Institute of Standards and Technology on measurement calibration at nist.gov informs how our instrumentation is maintained and verified between field assessments.
Structural findings also feed into the broader picture our predictive maintenance program tracks over time. Recording a structure’s baseline behaviour, alongside routine bearing-level readings, makes a future change in either data set easier to interpret.
Frequently Asked Questions
How is modal and ODS analysis different from routine vibration monitoring?
Routine monitoring focuses on the machine itself, tracking bearing and shaft condition over time. Modal and ODS analysis instead examines the supporting structure, identifying whether a baseplate, frame, or foundation is contributing to the vibration a machine displays.
When should a facility consider this type of testing?
It is worth considering when vibration persists after balancing and alignment have already been corrected. It is also useful when a new resonance appears after an equipment or speed change, or when planning a modification to existing rotating equipment.
Does this testing require the equipment to be shut down?
ODS testing is typically performed while the machine runs under normal load, so no shutdown is required. Modal testing with a controlled excitation can often be done during a planned outage window, if the equipment needs to be stationary.
What kind of report do we receive afterward?
You receive an animated deflection model, along with a written summary. It identifies the structural contributors found, ranked by significance, with practical recommendations for addressing each one.
Can this testing be combined with a standard rotating equipment assessment?
Yes, and it often makes sense to do so. Running modal or ODS testing alongside a routine bearing-level assessment gives a complete view of both the machine and the structure it sits on, in a single site visit.
Contact DVA Industrial Solutions Inc.
To ask whether modal and ODS analysis fits your facility’s current vibration issue, contact DVA Industrial Solutions Inc. at 7911 Masters Blvd SE, Calgary, AB, or call +1 (403) 437-0163. Our office is open Monday through Saturday, 7:00 am to 4:30 pm.