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What is Condition Monitoring? (Everything You Need to Know)


Condition monitoring (CM) is the process of monitoring a particular condition in machinery (such as vibration, temperature, etc) to identify changes that could indicate a developing fault. It is a major part of predictive maintenance as implementing condition monitoring allows for maintenance to be scheduled and preventive actions taken to prevent further failure and subsequent unplanned downtime.

Condition monitoring techniques are used on a range of equipment, including rotating machinery, auxiliary systems and parts such as compressors, pumps, motors and presses.

Traditional condition monitoring was mainly based around vibration analysis, but more modern, innovative techniques use sensors to measure different parameters in real time and can send an alert when a change is detected.


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TWI has experience of using condition monitoring techniques for a range of activities, including lifecycle analysis, material testing, leak detection and more.

We have worked on projects to develop and implement condition monitoring for wind power assetsship structures, engine machinery and other auxiliary systems, and more. In addition, we can provide training on condition monitoring systems and techniques, as well as developing our own suite of software.

You can find out more about condition monitoring at TWI here, or contact us, below, for more details.

How does it Work?

There was a time when condition monitoring as carried out by an engineer holding a wooden stick against a machine and feeling the vibrations to check if the equipment was running correctly. However, this has developed considerably with the use of digital technology, the Internet and advanced maintenance techniques (AMTs).

Modern ongoing real time monitoring means that engineers can schedule planned maintenance as required, rather than simply scheduling maintenance for a fixed date (i.e. every six months). This allows maintenance to be scheduled at a more efficient time, as and when required, leading to less downtime.

Condition monitoring can also prevent other components in a machine from failing as a knock-on effect from one part breaking down. This use of predictive maintenance is a great advancement from reactive maintenance, which involved running a machine to failure and then replacing either it or its components. This heightens efficiency and removes unexpected downtimes from a work schedule as well as minimising inspection procedures (You can find out more about corrective, preventive and predictive maintenance here).

Condition monitoring can be broadly broken down into three steps:

1. Install the Monitoring System

The first step in condition monitoring is to install the monitoring system hardware onto your serviceable equipment. This may require some retrofitting or modification of your existing assets, with different items of equipment requiring different approaches or instrumentation.

2. Baseline Data Measurement

With the monitoring system installed, you can begin to measure the performance of your equipment. The data collected can include vibration, rotor speed, temperature, and process sensor data. This will give you a baseline against which you can monitor your equipment against its optimum operating conditions going forward.

3. Ongoing Monitoring

The system can now monitor your systems using sensors and condition monitoring software that will evaluate performance and provide diagnostics. The system can also send out an alert when an operational abnormality is detected and assess the data to determine if immediate action is required or if the machine can operate for a while longer while maintenance is scheduled.

Condition Monitoring and The Internet of Things

The Internet of Things (IoT) is set to change condition monitoring as devices are able to connect and communicate with each other. This means that connected smart machines in different locations can communicate with each other to provide a joined-up comparison between systems.

This additional data will help engineers to make informed decisions about their machinery and any maintenance requirements. It can also improve diagnostic efficiency as the time it takes to carry out thermographic or vibration monitoring on one machine can now be used to test several machines simultaneously.

Connecting machines in this way can offer comparable data analysis of an entire production process regardless of whether the machines are carrying out similar tasks or not. As soon as a change in running levels is detected across the chain of production, operators can assess where the problems may be and act upon imminent faults.


Several different monitoring techniques can be used to evaluate the condition of your equipment. These include monitoring using sensors along with more physical techniques, such as checking for contaminants in machine oils.

While the different methods may indicate the same fault, they are best used together to deliver an overall picture of a machine’s operation. Each type of condition monitoring covers a range of different techniques to achieve them.

Condition monitoring types include:

Electrical Monitoring

Electrical monitoring involves the use of the principles of deviation in electrical parameters to find defects or faults. These parameters include capacitance, frequency response, induction, pulse response and resistance to locate potential issues. This method uses the measurement of degradation trends to determine whether action is required to prevent system failure.

Techniques include:

  • Alternating current field measurement (ACFM)
  • Battery impedance testing
  • High potential testing
  • Megohmmeter testing
  • Motor circuit analysis
  • Power signature analysis
  • Surge testing

Electromagnetic Measurement

This type of condition monitoring identifies cracks, corrosion, weaknesses and other defects by measuring field distortions and eddy current changes. Magnetic fields are applied to surface walls and, as they interfere with one another, they create patterns which can be used to identify deterioration in material quality and surface features. Also of use in tubing, electromagnetic testing shows defects as disturbances that can be measured and analysed. 

Techniques include:

  • Magnetic particle inspection
  • Magnetic flux leakage
  • Metal magnetic memory method
  • Pulsed eddy currents
  • Remote and near field eddy current
  • Saturated low-frequency eddy currents
  • Other eddy current testing

Laser Interferometry

Laser interferometry uses a highly accurate, laser-generated wavelength of light to measure changes in wave displacement. Based on the interference in light waves generated by a laser, it is used to locate subsurface and surface defects in materials including composites. It works by capturing and measuring the interference patterns using an interferometer. These patterns can show differences in material characteristics such as the presence of corrosion, cavities or surface defects in the material.

Techniques include:

  • Digital holography
  • Electronic speckle pattern interferometry
  • Holographic interferometry
  • Laser shearography
  • Laser ultrasonics
  • Strain mapping

Motor Circuit Analysis

MCA, or motor circuit analysis consists of a range of computerised tests on an electric motor to determine its condition and if there any possible sources of potential failure. MCA tests focus on electrical imbalances and degradation of insulation, which are the main causes of motor failure. The tests are usually split into voltage-based or current-based tests and include go/no-go tests and those that need to be tracked over time to determine failure development.

Inspections include:

  • Air gap
  • Insulation
  • Online and offline testing regimes
  • Power circuit/current signature
  • Power quality
  • Rotor
  • Stator

Oil Analysis / Tribology

As machines wear out or overheat, contaminants are deposited into lubricating oils, equipment fluids and other operating liquids. This technique collects and tests these oils, fluids and lubricants to reveal the presence of any contaminants in order to interpret how close a machine may be to failing.

Techniques include:

  • Dielectric strength testing
  • Ferrography
  • Fourier transform infrared spectroscopy
  • ICP / atomic emissions spectroscopy
  • Microbial analysis
  • Particle quantification index (to check iron content)
  • Potentiometric titration/total acid number and total base number
  • Presence of water tests
  • Sediment tests
  • Ultraviolet spectroscopy
  • Viscosity/kinematic viscosity testing

Performance Monitoring /Process Variable and Performance Trending /Observation and Surveillance

This most traditional type of condition monitoring involves visual inspections and the use of an engineer’s physical senses to judge how a machine is functioning. Used in conjunction with output tracking and manufacturing performance measurements allows an engineer to identify any deviations from the expected results, which could indicate a problem with the equipment. These types of inspection are still valuable today, especially when more advanced technological tests are not possible, although they are reliant on a degree of experience, record-keeping and expert interpretation.

Techniques include:

  • Audio inspection
  • Downtime analysis
  • Flow rates
  • Output or performance trends
  • Pressure
  • Temperature
  • Touch inspection
  • Visual inspection

Radiography/Radiation Analysis/Neutron Radiography

Some of the more thorough non-destructive testing methods, these types of condition monitoring use radiation imaging to find internal defects in equipment or parts. These methods are based on the differential absorption or radiation through a material, since corroded areas and flaws absorb differing amounts of radiation to unaffected areas. The absorption rates can be measured and analysed to find any defects and these techniques are also used to insect castings, sintered parts and weldments. 

Techniques include:

  • Computed radiography
  • Computed tomography (CT)
  • Direct radiography
  • Neutron backscatter
  • Neutron radiography
  • Positive material identification (PMI)

Thermography/Temperature Measurements/Infrared Thermography

Machinery and parts tend to heat up as failures develop, indicating misalignments, imbalances, poor lubrication, worn components, mechanical stress, or electrical overheating. Thermography can identify such thermal anomalies by capturing images of the thermal radiation patterns emitted from equipment, allowing the use of data collection and analysis to identify potential failures or part degradation. This type of condition monitoring is used to identify issues such as overheated electrical connections, pipe leaks or pressure vessel weaknesses.

Techniques include:

  • Comparative thermography
  • Comparative qualitative thermography
  • Comparative quantitative thermography
  • Lock-in thermometry
  • Pulse phase thermometry
  • Pulse thermometry
  • Temperature-related colour changing fluids
  • Temperature-related colour changing paint stickers

Ultrasonic Monitoring/Acoustic Analysis/Airborne Ultrasonic Monitoring

Ultrasonic monitoring techniques use high-frequency sound waves to detect part defects including leaks, part seating and cavities. Used for equipment, bearings and rotating parts, these methods can detect tiny changes in friction forces that may otherwise be missed using techniques like vibration analysis. These monitoring methods can offer an early warning system for machine part deterioration that may otherwise have been masked by ambient plant noise and temperature.

Techniques include:

  • Acoustic emission testing
  • Acoustic ranging
  • Airborne ultrasonics
  • Automatic and continuous ultrasonic inspection
  • Backwall echo attenuation
  • Dry-coupled ultrasonic testing
  • Internal rotating inspection
  • Long-range ultrasonic testing
  • Phased array testing
  • Time-of-flight diffraction
  • Ultrasonic backscatter technique
  • Ultrasonic thickness and gauging

Vibration Analysis/Dynamic Monitoring

Wear on machine parts, bearings, rotors or shafts can cause them to vibrate in unusual patterns that can be monitored, recorded and analysed. These vibration patterns can be used to identify defects and potential failures, including those due to misalignments, imbalances or even design flaws. Of course, technology has advanced since the days of holding a wooden stick against a machine (as mentioned above) but the theory remains much the same!

Techniques include:

  • Shock pulse analysis
  • Broadband vibration analysis
  • Fast fourier transforms
  • Power spectral density (PSD)
  • Spectrogram/spectrum analysis
  • Time waveform analysis
  • Ultrasonic analysis

Why it is Important

Condition monitoring is a tried and tested effective maintenance tool that is being used by an increasing number of industries. Condition monitoring systems provide important benefits from a financial, operational, and safety perspective.

While condition monitoring solutions may require some investment, these expenses are returned by preventing costly unplanned downtimes as a result of machine failure, as well as eliminating the unnecessary maintenance costs associated with scheduling maintenance based on operating hours rather than actual condition.

When used with connected systems, condition monitoring allows users to make the most of planned maintenance downtime, servicing multiple machines and addressing all problems simultaneously.

Proactive condition monitoring is also important from a safety perspective, as the effective monitoring and maintenance of machinery prevents accidents from occurring.

What are the Advantages?

As touched upon above, condition monitoring offers benefits for maintenance scheduling, operating costs, reduced downtime and safety. It allows users to determine whether an asset is likely to break down, what will cause the problem, and when the failure may occur. This gives owners time to organise maintenance before the failure happens, avoiding unplanned downtime and allowing repairs to be set for a suitable time in a production schedule.

As such, the advantages of condition monitoring include:

1. Avoid Unplanned Downtime

Avoiding unplanned downtime offers a range of beneficial outcomes for an industrial environment. By removing unplanned downtimes you prevent unplanned production delays which can lead to a loss of reputation if orders are not completed on time and the need to pay overtime to complete a job. In addition, there is no need to pay for an emergency call out to maintenance staff, which is more expensive than pre-scheduled maintenance.

2. Protect Your Other Assets

A machine failure can cause damage in other systems, compounding the problem further while also increasing repair or replacement costs. As a result, there will be no need to buy and store large numbers of replacement assets or parts in case of an unexpected failure. Instead, you will be forewarned of the need to replace a part and can order it as required in time for scheduled maintenance.

3. Eliminate Unnecessary Maintenance to Maximise ROI

Using condition monitoring as part of a predictive maintenance programme can increase the return on investment (ROI) of mechanical assets. Preventive maintenance programmes are set at regular intervals (i.e. annually) or after a set number of operating hours, irrespective of whether the maintenance is required or not. Through condition monitoring, it is possible to eliminate unnecessary maintenance and downtimes by only scheduling repairs when required. This means that you can get more working value from each machine, reducing the total cost of ownership and maximising the ROI for your equipment.

4. More Efficient Maintenance

Condition monitoring allows for more efficient maintenance by indicating where a fault may lie. This means that maintenance engineers do not need to check working components while locating the fault. This not only saves time and gets your maintenance completed faster, but also saves the cost of paying a maintenance engineer for wasted time.

5. Improved Safety

Checking and repairing machines before they break safeguards employee safety and helps ensure safer work practices. Condition monitoring means that owners can plan maintenance before failure occurs that could pose a threat to employees working nearby.

6. Improved Asset Efficiencies

Condition monitoring can also improvements the efficiency of assets. By having a record of which parts are running poorly, you can focus efficiency improvement efforts on those specific parts, thereby improving the overall capabilities of your equipment.

What are the Disadvantages?

Despite the many advantages to be found with condition monitoring, there are also some drawbacks; particularly related to the initial set-up of condition monitoring systems.

These drawbacks include:

1. Installation Costs

Condition monitoring equipment can be expensive to buy and install. In some instances, the monitoring systems may even require assets to be modified for retrofitting with sensors. There may also be additional sensor costs to take account of operating environments, further increasing the price of installation.

Some asset owners may decide that certain items of equipment are not worth the investment and prefer to either schedule regular maintenance for easily repairable items or even run to failure for non-safety critical items. 

2. Operational Costs

The ongoing data analysis required for condition monitoring will require either staff training to implement or the hiring of engineers with the required knowledge and experience. These will both incur additional costs, although this can often be offset by the many financial benefits of condition monitoring (as shown above).

3. Unpredictable Maintenance Scheduling

While condition monitoring offers many advantages for maintenance scheduling, some operators prefer to simply schedule maintenance on a regular basis. For example, it may be preferable to service a machine every six months, rather than waiting for it to show signs of wear at an unexpected time. However, most modern condition monitoring techniques offer advanced warning of a potential failure, offering plenty of time to schedule maintenance.


Condition monitoring has a wide range of applications right across industry wherever there is machinery or equipment in use.

It can be used in all forms of manufacture to check the efficient and safe running of machinery, preventing failure and the associated unplanned downtimes for repair or replacement.

Condition monitoring is also used to detect leaks, cavitation or flow, such as when managing piping, pipelines, pressure vessels and storage containers in the oil and gas industry.

CM techniques have also been applied to aircraft and aging vehicles, and has been used in the rail industry for vibration analysis of train door control systems and railway condition monitoring. These same techniques are also used to maintain other industrial assets, including in the marine environment and the power generation industries, such as the operational condition of a wind turbine's machinery and rotating components.

What is Online Condition Monitoring?

Online Condition Monitoring is used for the continuous monitoring of a machine or production process. Although this provides an uninterrupted process, many online systems will generate their most data during critical start-up and shutdown periods for a machine.

Because online condition monitoring systems can work remotely, they allow retrieval of data and analysis to be performed at a distance, managed by an external specialist.

Online monitoring systems send out warnings when pre-set limits are exceeded. These troubleshooting measures usually occur at lower limits than alarm values for fixed monitoring systems. This way they will indicate excessive wear and potential maintenance requirements rather than immediate risk.

By allocating the alarms to a specialist, any change in machine behaviour can be analysed immediately and, if necessary, action can be taken.


Condition monitoring is becoming increasingly common across industry as a method to ensure the safe working of assets and to improve efficiencies. Allowing for scheduled and directed maintenance and eliminating unnecessary procedures can save both time and money, while also ensuring production schedules are met.

While there are still some instances where preventive maintenance is preferred to CM-assisted predictive maintenance, many asset owners are realising the benefits of condition monitoring system.

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