Audible, Visual and Tactile Inspections for Predictive Maintenance Personnel

Lance Bisinger

Data collection is the backbone of any vibration monitoring effort, yet opportunities to gather additional data while at the machine are typically ignored. Is the vibration industry finally beginning to feel the effects of the pure data collector who has not transitioned into the reliability group from the mechanical trades? What about the site operators and craftsman? This paper covers basic inspection techniques that can be applied to optimize time spent in the field.

Many organizations separate personnel who perform technology monitoring into a predictive maintenance (PdM) team or reliability group. Their job is to periodically collect machinery information using various forms of technology and use this data to assess the condition of the machine.

Different technologies exist for monitoring the condition of mechanical and electrical components, and especially for detecting impending failure. Each technology has it own applications, advantages and disadvantages. Effective condition monitoring makes use of multiple techniques and technologies.

An under-utilized group of checks that provide valuable data are basic visual, audible and tactile inspections. These inspections can be performed and used to supplement the formal technology inspections. The key to successful implementation of a visual, audible and tactile inspection program is training the participants on the basic operation of the component to be inspected and following a list of items to be checked.

Condition monitoring steps
Effective condition monitoring programs consist of four major elements:

  1. Detection
  2. Analysis
  3. Correction
  4. Verification

It is important to thoroughly understand each of these elements. Valuable time is too often wasted when too much emphasis is placed on any one component.

Many problems can be found using visual, audible and tactile inspections. The goal is to identify bad machines or identify deteriorating conditions. The question becomes how to quantify the results of these inspections. Technologies like vibration, thermography, ultrasound, oil analysis and motor circuit testing may be used.

After identifying machines in need of further analysis using detection, the next step is to determine the root cause of the problem. This is achieved during the analysis phase.

Figure 1. Problem Detection

The purpose of performing an analysis is to determine the root cause of the problem. The analysis phase involves studying the machine’s operation, defect characteristics, maintenance history, etc. Only the machines indicating problems should be analyzed. Once the analysis is complete and the root cause of the problem found, the results should be communicated.

Figure 2. Problem Analysis

After determining the root cause of the problem, it can be corrected. The most common problems require balancing and/or precision alignment. In order to maximize the reliability of the machine in question, it is also advisable to improve the source causing the asset to be in exception. This will extend the life of the machine. We at Universal Technologies emphasize that the incremental time required to improve the machine is small compared to the costs of the unanticipated machine downtime and the maintenance process.

Figure 3. Problem Correction

After determining the root cause of the problem, correcting the problem and improving the machine, it is important to verify that the correction or improvement has occurred. One mechanism for this verification is comparing before values to the original baseline data.

Other common verification methods include:

  • Tracking increased bearing life
  • Tracking increased seal life
  • Measuring reduced energy consumption
  • Measuring vibration
  • Thermography
  • Oil analysis
  • Motor current signature analysis

Figure 4. Correction Verification

Visual inspections
One of the simplest, but often neglected, forms of condition monitoring is visual inspection of machinery. While this is subjective, you can often gain a good “gut feel” for where the problem is most severe. But remember, the root cause cannot be determined in this manner.

Effective visual inspection procedures include examination of the machine and surrounding area for each of the following:

  • General cleanliness
  • Oil/fluids on surrounding machine
  • Oil/fluids on machine casing or bearing caps
  • Oil/fluids on coupling guard
  • Unusual marks
  • Visible leaks (lubricants, cooling water, etc.)
  • Lighting conditions
  • Local instrumentation for proper levels, temperatures, flows and amperage
  • Fretting and wear particles
  • Corrosion
  • Signs of overheating
  • Proper operation of slinger rings
  • Condensation/water in bearings
  • Differential temperatures, pressures and flows
  • Loose parts or components
  • Machine guard or cover condition

Figure 5. Housekeeping

Figure 6. Oil Leak

Figure 7. Frame Crack

Figure 8. Motor Fan Cover

Figure 9. Oil Condition

Audible inspection
Another simple form of condition monitoring is audible inspection of machinery. While this is also subjective, you can often gain a good “feel” for the area where the source is originating. But remember, the root cause cannot be determined in this manner. The use of stethoscopes, sounding rods and other listening devices can enable an experienced practitioner to detect such problems as rubs, bearing defects, cavitation, etc.

When listening to a machine, try to determine if the sound is complex or simple, high frequency or low frequency, and from where the sound appears to be coming.

Effective audible inspection procedures include examination of the machine and surrounding area for the following:

  • Sounds that are out of the ordinary
  • Humming
  • Squealing
  • Growling
  • Rubbing
  • Cavitation
  • Arcing/popping sounds
  • Hunting/beats
  • Noise from leaks
  • Comparison noise from bearings
  • Water hammer
  • Lifting sentinels/relief valves
  • Flow through system / components

Tactile inspection
To hand-feel a machine for excessive vibration, perform the steps below:

  1. Start at the bearings, feeling in vertical, horizontal and axial directions.
  2. Work downward and outward from the machine, feeling the base, structures, pipes, pipe supports, valve stems, electrical boxes, electrical conduit, etc.
  3. Try to get a sense of the frequency of the vibration. For instance, is it high frequency, such as a buzz or a tingle? Or, is it low frequency, such as a shudder or a sway?

Figure 10. Motor Check

Other tactile observations should be performed as well. Effective tactile inspection procedures include examination of the machine and surrounding area for the following:

  • Temperature comparisons on bearings
  • Temperature comparisons on seal flush systems
  • Temperature differences on cooler / heat exchanger inlet and outlet
  • Temperature differences on filters / strainers inlet and outlet
  • Feel oil for contaminants and metal particles
  • Feel for flow through systems / components

Enhancing visual inspections with spot radiometers
Infrared thermometers measure the amount of infrared energy emitted by a target object and calculate the temperature of that object’s surface. Typical features include laser sighting, adjustable emissivity, alarm functions and trigger locks. Other features may include data loggers and graphic displays, thermocouples, and software interfaces.

It should be noted that the temperature reading is the outer surface temperature of the first surface the laser beam penetrates. If taking a reading through Plexiglas or other transparent material that the laser penetrates, the temperature reading will represent the Plexiglas surface only.

Figure 11. Spot Radiometer

Limitation – emissivity: Emissivity is ability of a material to reflect heat. Different materials have different emissivity values and must be accounted for when attempting to obtain an absolute temperature reading. For comparison readings, emissivity is less of an issue provided that the two target materials are the same. If there is a need for accurate absolute temperature measurement, then the contact thermocouple provided should be used to cross-check the infrared data. Your instrument has functions that allow you to select the correct emissivity value for the target material, but for the intent of this article and general instrument use, the “free” setting will be used.

Limitation – measurement spot size: The measured spot size depends on the distance between the object you are measuring and the infrared thermometer. This will vary depending on manufacturer and by models from the same manufacturer. Note that the temperature is an average of the temperatures contained within the spot circle. Move closer to the target to get a smaller measurement area.

Strobe lights
Visual inspection of rotating assets in conjunction with using a strobe light allows other components to be evaluated.

  • Coupling, shaft and key condition
  • Leak detection from bearing caps, mechanical seals and couplings
  • Mechanical looseness of machine components
  • Belt condition
  • Even tensioning / loading of belt drive systems

Figure 12. Strobe Light

Precautions and safety:

  • Objects viewed with this product may appear to be stationary when in fact they are moving at high speeds. Always keep a safe distance from and do not touch the target. Be aware of others in the area and take responsibility for their safety by warning them of these precautions.
  • Use of this equipment may induce an epileptic seizure with those prone to this type of attack.
  • Do not allow liquids or metallic objects to enter the ventilation ports on the stroboscope to avoid damage to the instrument.
  • Caution – there are lethal voltages present inside the instrument. Refer to manufacturer’s literature for lamp replacement procedure before attempting to open the instrument.
  • To assist in the inspection of couplings and belts with a strobe, it is recommended to use expanded metal with a flat black finish for coupling and belt guards whenever possible. This permits the user to see through the guard with a minimum of reflection.

Performing visual, audible and tactile inspections can provide tremendous value when integrated into an overall reliability effort. Formalizing and documenting inspections that are being performed by non-PdM technicians will allow data to be utilized by everyone.

The acceptance of integrating technologies to gain a better picture of equipment condition is widely accepted. Why not use this same model to leverage information from personnel who traditionally are not viewed as having an active role in reliability? Many times, operators and maintenance personnel can provide that “missing piece” of information that cannot be seen by the PdM technician when viewing equipment on a monthly or quarterly cycle.

How many organizations would jump at the chance to add dozens of additional personnel to the reliability effort without adding additional cost? By training and engaging operators and maintenance personnel, that is exactly what is possible.


  1. “Operator Care for Machinery Reliability”, Universal Technologies Inc., Huntersville, N.C., 2005.
  2. “Vibration Analysis Level 1 Plus”, Universal Technologies Inc., Huntersville, N.C., 2005.

This paper was presented at an annual Noria Corporation conference. 

About the author:
Lance Bisinger is the Americas operations manager at GPAllied, a reliability and operations consulting and services company. For more information, visit

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About the Author

Lance Bisinger is the Americas operations manager at GPAllied, a reliability and operations consulting and services company. For more information, visit Read More