Revealing Defects in Belt Drive Systems

In this short video, Rob Dent (CMRP, CRL) from SDT, details the use of ultrasound technology to detect faults in belt drives.


One small but vital component of many machines is the belt sheave. Belt sheaves can sustain damage from everyday wear and tear, misalignment, and contamination.

The benefits of using ultrasound to find defects in belt sheaves:


  • Early Detection: By regularly scanning belt sheaves with an ultrasound device, maintenance teams can detect unusual sounds that indicate wear or misalignment early on. This early detection allows for timely intervention before a minor issue becomes a major problem.
  • Non-Invasive Check: Using ultrasound is non-invasive, meaning you don’t need to stop production to check the condition of the belt sheave. This makes the process quick and hassle-free.
  • Precision: Ultrasound technology provides precise information about the condition of the belt sheave, helping maintenance teams pinpoint the exact problem and take appropriate action.


Using ultrasound to detect bad belt sheaves is a smart, efficient way to maintain machinery. It allows for early detection of issues, saving time, money, and increases safety.

Our recommended SDT ultrasound tools for belt sheave inspection.




Visualizing Success: Incorporating Pictures to Routes with SDT340


Setting up routes using SDT UAS3 software with the SDT340 includes a feature that greatly adds to the efficiency of the measurement taking process.

Some routes can have dozens or even hundreds of measurement points. By adding pictures to the measurement data in the UAS3 software it allows the user to specify the locations where data will be collected. When the route is uploaded to the SDT340, the pictures can be displayed on the screen while taking data. With the picture feature, technicians can visually confirm each measurement point, providing a clear reference.

UAS3 location identification

Pictures can be added to measurement points in the UAS3 tree structure. Then when sensors are added to the measurement point, an icon will be displayed on the picture representing that sensor. The sensor icon can then be moved around in the picture to represent the exact location on the machine that the sensor should be mounted to record data.

SDT340 measurement points, pictures to routes sdt340

The route is then uploaded to the SDT340. When the technician brings up a measurement point, the pictures can be viewed by pressing F1, helping the technician to verify where the data should be collected.

SDT340 measurement points zoomed

The picture can then be zoomed in with F1, out with F2 and scrolled with the navigation arrows as needed.

Click here for more information on UAS3
Click here for more information on the SDT340

Precision Bearing Lubrication

It’s been said that Industry runs on a 10 micron film of oil… it’s important we get it right. Using ultrasound to monitor the addition of grease to the bearing allows us to ensure that the proper amount is being added.

In this video, Rob Dent CMRP, CRL details precision lubrication with ultrasound. Using the LUBExpert, SDT270 or SDT340 also allows us to trend and monitor the bearing condition every time the bearing is greased. 


By using ultrasound technology, you can detect sounds that indicate whether a bearing needs lubrication, a valve is closing properly, or there is an air leak.

These sounds can provide valuable insights into the condition of your machines and help you identify defects before they become major issues.

To schedule a in-person or virtual demo fill out the form below.





SonaVu air leak detection

Selecting an Ultrasound tool for compressed

air and vacuum leak inspections


Air Compressor Costs

Compressed air and vacuum leaks

Finding and fixing compressed air and vacuum system leaks is a cost-effective and environmentally responsible practice that can improve energy efficiency, reduce operational costs, enhance equipment performance, ensure safety, and contribute to the overall productivity and sustainability of your operations.Below is a comparison of the different ultrasound tools available to find those leaks.

Methods of measurement

Ultrasound tools for finding and fixing air, gas and vacuum leaks are available in two basic formats, the hand-held ultrasound tool and the acoustic imaging camera.

The hand-held tool has been around for many years and is typically used with a single flexible airborne sensor, a tool mounted airborne sensor, a hand-held airborne sensor or a parabolic dish for long distances. To operate this tool the user would be wearing a headset to listen while scanning with the sensor for ultrasound. When a leak is found it can be heard in the headphones as well as seen on the tools’ display as the values increase. On some tools the leaks can be recorded as overall values on the device and stored and analyzed in software, on others external apps may need to be used to store and report on the leaks.

Advantages to a hand-held ultrasound tool:

  1. Typically less expensive than an acoustic imaging camera and there is a wide range of options and capabilities.
  2. Some hand-held tools also have structure borne sensors available allowing many other uses for the tool besides leak testing.
  3. It is sometimes easier to get the external sensor into tight or hard to access areas.

The acoustic imaging camera is a more recent technology that uses many microphones (over 100) to listen for leaks and then overlays the leak location on a color video screen. The user will also be wearing headphones and listening for the leaks. Wearing the headphones will help distinguish other sources of ultrasound from the air leak allowing you to be confident in their identification. This makes identification of the leaks fast and easy.

Advantages to an acoustic imaging camera:

  1. Because you can see and hear the leak the acoustic imaging camera makes finding leaks fast and easy.
  2. Recording the leak also takes a picture of the location and notes can be added as well.
  3. Minimal training required for the technician to get comfortable using the tool.


The SDT LEAKChecker and ULTRAChecker are entry level systems to help you find leaks. Both systems show the ultrasound level on the display and allow you to listen through the headphones to ensure that the ultrasound you are measuring is actually an air leak and not another source of ultrasound.

The LEAKChecker is a dedicated system to measure leaks and has a built-in flex sensor. The ULTRAChecker includes a flex sensor, but also has the capability to use all of the SDT airborne and structure borne 2nd generation sensors. With the additional sensors you can add lubrication, bearing condition, steam traps and more to the capabilities of the tool.

SDT LEAKChecker 1

SDT200 leak detection


The SDT200 is the next level up from the checker series tools. An SDT200 can also use all of the 2nd generation sensors so it covers the full range of ultrasound capabilities. SDT200 includes Datadump software to do basic reporting of static ultrasound measurements. Air leak surveys are done using the onboard sensor, Flexible sensor, EDS sensor, ParaDish2 or AirSense sensor or a combination of sensors as necessary.

SDT270 air leak


The SDT270 is an advanced ultrasound tool that includes either Datadump or SDT’s Ultranalysis 3 software. It also uses the 2nd generation sensors and adds temperature, RPM and vibration measurements. With the UAS3 software you can create a database and routes to trend data. This data is displayed as overall, time waveform and spectrum for analysis. In addition, an audio recording is taken with each dynamic measurement so it can be reviewed as needed. Air leak surveys are done using the onboard sensor, Flexible sensor, EDS sensor, ParaDish2 or AirSense sensor or a combination of sensors as necessary.


The SDT340 takes all of the SDT270 capabilities to the next level. It offers longer and faster recording times using all of the second gen SDT sensors. Data can be analyzed directly on the color display unit without having to download to the included UAS3 software. This data is displayed as overall, time waveform and spectrum for analysis. The SDT340 also adds the ability to measure and analyze vibration data. This data is also displayed as overall, time waveform and spectrum for analysis. Air leak surveys are done using the ULTRAsense sensor, Flexible sensor, EDS sensor, ParaDish2 or AirSense sensor or a combination of sensors as necessary. For example you may use the ParaDish2 for long distance and the Flexible sensor up close.

SDT340 air leak inspection

Sonavu air survey


The SonaVu makes finding, recording, reporting and monetizing leaks easy. It is an advanced acoustic imaging camera with 112 built-in MEMS microphones so you can see and hear the leaks. It records data, images and video (including sound) on a 53GB internal drive. With the included SonaVu Insights software you can export data and images and calculate the costs of each and every leak. Using that data you can produce detailed reports and keep track of what has been repaired and what hasn’t. The SonaVu also has built-in Bluetooth and an audio jack so you can listen while doing the leak survey to hear and see the leaks.


Want to hear more? For more information or a demonstration of any of these tools, please Contact Us






The sounds of maintenance are often unheard by the human ear, but they can reveal  information about the health of machines in your facility. By using ultrasound technology, you can detect sounds that indicate whether a bearing needs lubrication, a valve is closing properly, or there is an air leak. These sounds can provide valuable insights into the condition of your machines and help you identify defects before they become major issues.

This quick video showcases the use of ultrasound technology during routine inspections, capturing some healthy and defective sounds of maintenance. Through audio and visual demonstrations, you can see and hear the differences between the two conditions.

SDT 340 Ultrasound tool


Ultrasound Detection:


Reliable Plant Article written by Allan Rienstra from SDT Ultrasound Solutions.

The popularity of ultrasound inspection for maintenance and reliability managers is attributed to ease of use, versatility and low implementation cost. Once considered a companion to core predictive technologies like vibration analysis and infrared imaging, the emergence of standalone ultrasound inspection programs is more prevalent for reliability departments today.

Ultrasound is now considered a front-line defense system in the everyday battle for manufacturing uptime. Airborne ultrasound is predictive maintenance for the masses.

Mass Appeal

The applications in which ultrasonic technology can be used are nearly limitless, lending to its mass appeal. Compressed air leak detection, condition-based monitoring of bearings and acoustic lubrication of bearings are popular applications.

Some inspectors monitor thousands of steam traps and pinpoint in-leakage to boilers, condensers and heat exchangers. Others marry ultrasonic inspection and infrared scanning together for added safety to motor control center panel scans or surveys of high-voltage substations and transmission and distribution lines.

Easy to Use

Ultrasound instruments have always been considered user friendly. Being painted this way left consumers with the impression that user-friendliness equated to lacking sophistication.

Nothing could be further from the truth for the new generation of instruments. Inspectors can literally design their own instrument to suite their program’s needs and goals, and flexibly change that instrument as their program evolves.

Most detectors work on the basic principle of detecting high-frequency ultrasound and converting it to corresponding audible sounds, which can be listened to with headphones. Additional functions are dependent of the device, but most provide a visual indicator on a bar graph display or a decibel measurement.

Some can even capture a time-specified wave signal that can be analyzed with software. Adding sophistication while maintaining simplicity is a challenge that some manufacturers handle better than others, but the net effect is driving the popularity of this technology to mainstream predictive maintenance (PdM) practitioners.

Ultrasonic analysis offers benefits for all areas of the manufacturing process. Most machine failures could be discovered early, making them treatable issues instead of replaceable downtime issues. Excessive vibration and temperature increases are indicators of mechanical failure on the horizon, but we also learned that microscopic changes in friction forces, detectable early with ultrasound, provide a bigger window of opportunity for scheduled maintenance.

When you hear problems this soon, you are empowered with the ability to limit downtime and overall maintenance cost. Following are some of the most common maintenance applications for airborne ultrasound that can be applied at plants today.

Compressed Air Leak Management

Compressed air is one of the most expensive utilities used in manufacturing. Leaks are expensive and often ignored. While they can be heard with the naked ear, they are difficult to pinpoint because of background noise.

An ultrasonic detector hears leak turbulence through the ambient noise of the factory floor no matter what. The high-frequency component of a leak is directional, making it fast and easy to locate its source.

A compressed air survey with an ultrasonic detector once per quarter will reveal savings potential in the millions and benefit plant managers looking to improve efficiency and reduce costs.

Condition Monitoring

One application that has evolved alongside the new generation of detectors is condition-based monitoring (CBM) of rotating and non-rotating equipment. In both instances, production machines produce frictional forces with high-frequency ultrasonic signatures.

These forces are often masked by ambient plant noise and low-frequency vibrations. Changes in these signatures serve as early indicators of failure and provide comparative information for vibration data.

You want to believe that the majority of your machines are not in an advanced failure condition. Would you rather spend days analyzing gigabytes of data from machines that are not failing or use ultrasound technology to sort the good from the bad so your vibration analysts are focused only on trouble areas? The answer is obvious and reasonable.

Ultrasonic instrument equipped with digital decibel-metering measures and logs the intensity of high-frequency frictional forces. Enhanced detectors also capture time signals alongside the decibel measurement.

Time signals are useful for slow-speed bearing condition assessment, which is one area where vibration analysis struggles.

Condition monitoring with ultrasound provides overall data that is indicative of elevated friction levels from random impacting, rubbing and spalling. These non-sinusoidal events are more interesting to analyze in the time domain, making ultrasonic monitoring useful as a first line of defense instrument.

Collecting information is quick and inexpensive. Much more data can be taken, extending condition monitoring to more machines that may have been overlooked by vibration due to time and costs.

Ultrasonic monitoring will detect a change earlier in the fault cycle than other technologies. For this reason, ultrasound is generally used to alert changes in condition and for a preliminary diagnosis.

Acoustic Condition-Based Lubrication

Over time lubrication breaks down, and the friction forces inherent in any bearing increase. Ultrasonic systems that measure decibel-microvolt levels monitor and predict the relevant need for regreasing of the bearing.

When a baseline ultrasonic alarm is compromised, a lubricator is alerted to the problem and can correct it before the bearing is physically damaged.

Condition-based lubrication monitoring advises lube techs when grease is needed and warns them when too much grease is added. One problem with adding too much grease is compromised seals. For electric motor bearings, this means grease pushed through the seal and into the windings.

One U.S. paper mill decided to stop greasing motor bearings altogether since it was cheaper to replace the bearing instead of cleaning out piles of grease from the motor. This technique has become the norm for establishing lubrication requirements on most production machinery.

Electrical Applications

The versatility of ultrasonic inspections extends to the electrical maintenance department where routine scans of switch gear, substations and high kilovolt transmission and distribution lines are commonplace. There is mounting concern about safety, specifically the danger of arc flash.

Prior to opening high and medium voltage electric panels, inspectors use ultrasound detection to listen to the levels of ultrasound inside the cabinet. The importance of finding problems at an ultrasonic level can’t be overemphasized.

Radio and TV interference are common complaints from local cable companies. Often the source can be traced to a faulty transformer or a failed lightning arrestor.

Pinpointing the culprit is quick and simple with an ultrasonic scan. The directional nature of ultrasound focused on a parabola reveals problems from a safe distance.

Steam System Inspections

A steam trap is an automatic valve that opens for condensate and non-condensable gases and closes for steam. It is designed to trap and remove water, air and carbon dioxide, which hinder the efficient transfer of steam, corrode system components and cause damaging water hammer.

Ultrasonic surveys of the entire steam system will reveal system leaks, blockages, stuck valves and failed traps. Increasing steam efficiency translates to huge dollar savings and increased product quality. Certain types of traps can benefit from dynamic signal analysis.

When monitoring continuous traps, it can be difficult to discern between live steam from a failed trap and flash steam, which is produced when the reduced pressure of the condensate line causes condensate to regenerate back to steam. Viewing the time signal of suspect traps can help distinguish between flash and live steam.

Pump Cavitation

Cavitation is the result of a pump being asked to do something beyond its specification. Small cavities of air develop behind the vanes. These pockets have a destructive effect on the pump’s internal components. During normal data collection, inspectors use ultrasonic detectors to isolate random cavitation, which can be masked by low-frequency modulations.

By using an ultrasonic detector in contact mode, you can isolate the pump vanes and listen for small air pocket explosions. Place the contact probe on the housing of the pump vane and adjust amplification to filter down shaft noise. With some experience, an operator will quickly be able to identify when pump cavitation is present.

Reciprocating Compressors and Valves

Reciprocating valves give breath to compressors. Worn or dirty valves can’t seat properly. Over time springs weaken, limiting the force necessary to snap open and closed, which causes leakage. Valve condition is monitored with ultrasound inspection and spectral analysis software. The demodulated signal from the detector is fed directly to an analyzer or stored as a wave file. Spectra graphs visualize the compressor valve as it opens and closes, as well as intakes and exhausts.

Visualizing the recorded sound file of a compressor valve can tell you a lot about the condition of the valves and their components. Valves are opened and closed by a spring mechanism, allowing reciprocating compressors to intake and exhaust.

The three distinct events (open, intake or exhaust, and close) all occur at split-second timing that is too fast for the naked ear to process. By viewing the wave file in real time, you can stretch this out to visualize each individual event. Time wave images can also be saved and compared over time to see the evolution of wear.

Heat Exchanger and Condenser Leaks

Tube condensers and heat exchangers cool steam, which condenses back to purified water and is returned to a boiler where it is superheated back to steam. Leaks in the tube allow contaminants in, opening the door for corrosion and reduced operating life. Keeping the water pure is the key to efficiency.

The general method of inspection involves scanning with the instrument a couple feet from the tube sheet. If a noisy area is found, it is noted. However, if you switch to an extended flexible sensor, you can scan tube to tube.

If the sound signal on the digital decibel-microvolt meter or the sound in the headset does not change from tube to tube, a leak is unlikely. This is particularly true of tubes located on the outer edges of the tube sheet, as these tubes are more likely to have noisy steam flowing over their outer diameter surfaces.

If a significant signal change occurs, then a leak is suspected. If the leak is within the tube, the difference will be heard at the tube opening. If the noise level is heard on the tube sheet, block the area to eliminate reflected noise, then place a rubber precision tip with an opening of 1/8 inch on the flexible extended sensor and hold it almost on the tube sheet surface.

Valves and Hydraulic Leaks

Over time small leaks, blockages and bypassing will manifest inside hydraulic systems. The sources of these faults are detectable with ultrasonic inspection. Hydraulic oil will form small bubbles, which pop as they are forced across seals and wipers. With a magnetic or contact sensor placed against the housing, you can set the sensitivity to the maximum level to reveal the tiny explosions.

The signatures from a passing hydraulic valve can be a steady rushing sound or an intermittent gurgle. Comparing similar areas in the system to trace blockages and passing will save hours of visual inspection and tear down time.

Where Do We Go From Here?

Ultrasonic inspection, detection and data collection have been around for more than 35 years but only recently have gained acceptance in predictive maintenance departments. Branded as “ultrasonic leak detection,” this technology has shed its type-cast role to become a versatile, important and dynamic member of the predictive family.

Beware of the technology trap. Buying the latest and greatest gadgets, even the useful ones like ultrasound, will only take you so far. For a successful and long-lasting ultrasound inspection program, be prepared to invest in a program implementation specialist to help you establish your goals, plan for the execution of those goals and institute a means to measure the progress of your program as the benefits start rolling in.  Click here to view our available SDT Ultrasound product range.

About the Author

Allan Rienstra is the president of SDT Ultrasound Solutions and co-author of “Hear More: A Guide to Using Ultrasound for Leak Detection and Condition Monitoring.”



SonaVu Electrical survey


Ultrasound and High Voltage




Precise was part of an ultrasound training course at a steel plant in Ohio. During training, the maintenance manager learned about measuring for Corona, arcing, and tracking with an ultrasound tool. We were asked to take some readings of their high voltage towers to detect if there was any indication of potential Corona damage. Corona can be easily detected by ultrasound above 2,000 volts.

The previous week a transformer below the high voltage insulators failed. (The input voltage exceeded 100,000 volts and was coupled down to 800 volts in the transformers. This was used to provide the high current needed to melt the steel.)

A time waveform signal and spectrum were taken using an SDT270. We took the measurements with a parabolic sensor because of the high voltages present and distance needed for safety. There were four condition indicators collected; RMS, max RMS, peak, and crest factor. RMS is the average signal and max RMS is the average of the twenty highest peaks.

Peak is the highest value recorded during a measurement and crest factor is the level of severity using a ratio of peak to RMS. The key indicators for this application are peak and crest factor.

As shown in the spectrum below the signals have spikes that relate to 60 HZ and its harmonics. The 60HZ spike and its harmonics validate the source of the time waveform. This noise could be a precursor to damage. (Corona has a build-up and drop-off of energy, resulting in a buzzing sound accompanied by subtle popping noises.)

The proper way to analyze the data is to trend over time and take note of the changes in the time waveform and the condition indicators.

Using ultrasound for electrical inspections can enhance the possibility of detecting anomalies and increase safety during inspections.



These measurements were taken with an SDT270 ultrasound tool with a parabolic dish. 


These measurements were taken with an SDT270 ultrasound tool with a parabolic dish. 

These measurements were taken with an SDT270 ultrasound tool with a parabolic dish. 



is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor carrying a high voltage. The air has undergone electrical breakdown and become conductive, allowing charge to continuously leak off the conductor into the air.



 is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally non-conductive medium such as air produces a plasma; the plasma may produce visible light.




is the formation of partially conductive, typically carbonized, pathways on the surface of insulating materials by electrical breakdown arcing. This ‘track’ is then an easier path for electrical leakage.








Common ultrasound applications are electrical inspection, lubrication, leak detection, condition monitoring, steam trap inspection and tightness testing.

Recommended tools for electrical inspections are the SDT270, SDT340 and SonaVu