When companies begin exploring incorporating ultrasound technology and devices into their preventive maintenance (PM) and predictive maintenance (PdM) programs it can be very confusing for first time buyers. In the ultrasound marketplace today there is a lot of hype, a wide range in prices, and more often than not, mixed and confusing messages as to the true capabilities of these devices and the results one might come to expect. Let’s begin by stating that ultrasound is not a replacement for other technologies such as infrared thermography, vibration analysis or fluid analysis but rather a complimentary and valuable technology. Ultrasound provides companies more information about the health of their physical plant and often provides this information earlier than other technologies. By being able to “listen” to your plant’s equipment and machinery, one can detect nuisances and abnormalities well in advance of the development of other characteristics such as heat buildup (detectable through thermography and fluid analysis) or audible detectable physical changes (vibration analysis).
How to look for what’s important versus the extraneous
Within each of these key factors to consider are guidelines that will help you find the answer. Listed below is some tale telling things to be looking for and why. Too much emphasis on product differentiation for the sake of being different may simply be to confuse buyers with bells and whistles. We’ll take an examination of some of the fluff that’s out there and filter down to what’s really important and guide you to the right product criteria.
Digital versus Analog Meters
Sound is analog by nature. To display sound levels with a digital meter requires first converting the ultrasound amplitude to digital then sampling or averaging the numbers, otherwise the digital meter would be changing so fast as to be unreadable. So digital meters will display either a peak number or an average. This is far less accurate than an analog meter displaying the signal strength in real time. Analog users just have to watch the needle rise as you approach the sound source. Analog meters indicate both real-time amplitude, amplitude over time, spikes or valleys (indicating anomalies, especially for rotating machinery). Digital meters typically also draw down a battery faster. The only time you need to digitize the sound is to record them, which has nothing to do with meters. In the next paragraph you’ll see another major drawback for digital meters.
Clearer Reception / Less Background Noise
Most all ultrasound devices can hear loud ultrasound. However, for most applications, you want to hear even low amplitude ultrasound whether it’s for leak detection in pressurized air/gas/vacuum systems or to be able to differentiate between bearings (normal, under lubricated, defective). One of the biggest problems for first time ultrasound users is being able to distinguish detectable low volume ultrasound from any inherent background noise that the device itself may introduce. This is particularly true of lower quality ultrasound devices. Be aware that digital meters and displays through their electronics induce background (“white”) noise. Analog displays do not have this characteristic and therefore provide clearer and sharper sound to the headset.
Also, the methodology used to convert or bring the ultrasound down into the human audible range can vary significantly from one device to other. Superior technology allows you to hear down converted sound that is a more characteristic representation of the original sound. Some conversion technologies including heterodyning may allow for distortion or warble of the original sound. Heterodyning that may be great for music maybe but not necessarily for ultrasound based diagnostics. Also, with a quality ultrasound device, you should hear silence when there is no detectable ultrasound. A technician should leave the guesswork out of the equation when trying to distinguish background noise from detectable ultrasound. A quality device will not have electronics that introduces background noise resulting in more guesswork, more false positives, and less consistent diagnostic results.
Ease of Operation
There are many products out on the market that try to differentiate themselves by adding bells and whistles that only complicate the usage. They try to convince potential buyers that these features allow them to detect ultrasound that they wouldn’t otherwise. Take the ability to adjust frequencies. For some ultrasound devices this may be a necessary evil. One such example is having to lower the frequency to hear something such as a water leak. Fact is that the sound propagation of a water leak sweeps over a range of frequencies, not just one. Making users change frequencies for different applications also has the drawback that if not properly set to the right frequency, you may miss a leak or abnormality. Adjustable frequency settings may be a product differentiator but try to stick to the essentials. Choose a device that allows users to more intuitively use it without complicated settings and less likely to be misused.
Your plant engineers are going to be out on the plant floor taking dozens and dozens of readings over several hours. The form and fit of the device can play into how likely the user will want to shorten his time using the device. With some pistol style devices, you have to squeeze a trigger to turn it on. After you release the trigger, it will turn off within a few seconds. This is to conserve battery life. And, at the end of the day, your hand will feel like it’s been squeezing a trigger on and off all day. Some devices, especially with LED displays, often have auto shut-off mechanisms to conserve battery life. You want a device that when you turn on, it stays on. Put it down, write a note or tag a leak, its still on until you decide to turn it off. There are advantages to acquiring a device that is meant for true one-handed operation, even when adjusting the sensitivity. It is preferable to not have to use one hand to hold the device while the other hand adjusts a knob or changes a setting.
Just like with the ergonomics of the ultrasound device, weight is also an issue. Again, we are talking about carrying this device for hours out on the plant floor pointing and probing throughout the day. Lighter weight is good. Some devices, especially with built in recording capability, weigh over two pounds. That can be fatiguing after hours of use. If you need recording capability, select a device wherein the recording end of the device can be worn on a belt pouch or in a pocket. Remember, you most likely will be using the same hand to use and carry the device all day. Ideally, you would want a device that the recording electronics and housing can be detached from the receiver for applications that don’t need recording such as air leak detection.
The higher quality ultrasound devices that use standard disposable batteries typically give you 3, 4 or-5 months of normal usage or roughly 40-50 hours continuous use. However, there are a number of low-end devices that sometimes will give you only 8-10 hours of use. Check with your vendor’s specifications. With a rechargeable, the battery life is shorter (thus they have mechanisms to turnoff automatically to conserve battery). If you or coworkers forget to recharge it overnight you can lose valuable on-floor time the next day while waiting hours for it to recharge. Stay away from devices that use specialty batteries that are hard to find and are expensive. Good advice is to keep a fresh spare battery with the kit. Make sure your device has a battery meter to indicate when to change it.
Some ultrasound devices require them to be sent back to the factory for recalibration. This adds additional time and expense just to keep the unit viable. The fact that these devices need to be recalibrated periodically raises the question of why. If their sensor is prone to drift over time, that would imply distortion of the signal integrity which can be significant on any recordings. Devices that do not require calibration are preferable, as they inherently will give consistent performance over the years.
Growth path to greater application usage
Look for an ultrasound device that offers a clear growth path for expanding the application uses. Ideally you want to use the same receiver for all your ultrasound applications. Conversely, you don’t want to have to change devices to add expanded applications or capabilities such as data recording and analysis. Also beware of single application devices such as lubrication specific or alignment specific products. A good ultrasound device should be able to do these applications with the proper attachments.
Real-time Data Capture, Verification, and Analysis
Some of the more sophisticated ultrasound devices allow data capture and analysis. This is very valuable for Predictive Maintenance (PdM) programs. These devices should include the ability to visualize your recordings in waveform simultaneous to the recording and with some instant signal analysis. Recordings should be able to playback immediately while still at the test point. You wouldn’t want to wait until you have completed your route and then later have to verify that the recorded data was good or even recorded. This ability to verify quality of the recording combined with instant signal analysis and playback is not found in all data recording capable devices. Also, compare the quality of the displays for better visualization of ultrasound signal anomalies including crackles (sharp spikes in the amplitude). Look for recording devices that employ a separate add-on PDA or Pocket PC which typically have more computing and storage capabilities than built-in recorders. This allows the user to store more routing information, more routes, more data, more samples, and more applications such as spreadsheet and notepad applications.