Compressed air systems provide critical services in a vast array of industrial facilities and often represent the majority of a facility’s energy costs. It is vital, therefore, that operators of facilities with compressed air systems do their utmost to ensure that their compressed air systems run reliably and at peak efficiency year-round. This is often achieved through the use of technologies such as vibration analysis, infrared cameras, shock pulse monitoring and portable dewpoint sensors. Today, we will have a look at the application of these technologies in compressed air systems.
Vibration analysis
Compressor vibration analysis is a key part of the condition monitoring program of any compressed air system. It involves the measurement and recording of overall vibration values to help determine general machine condition or very specific machine disorders, such as bearing wear or rotor degradation. The goal is to detect early on any potential equipment failure to avoid costly breakdowns and reduce maintenance costs.
There is a wide range of vibration sensors used on compressed air systems, and new MEMS technology (micro-electrical-mechanical system) makes them much smaller and more affordable, allowing more of them to be placed on the components of compressed air systems to determine vibration sources more accurately. New smart vibration monitoring systems incorporating MEMS and IoT (Internet of Things) technologies are truly advancing vibration analysis for compressed air systems. IoT technology provides wireless connectivity so that experts can gain near-real-time visibility into machine conditions without traveling to locations.
Benefits of new smart vibration monitoring systems
- Continuous and cyclic acquisition of overall vibration values
- 24/7 remote monitoring, eliminating costly old-fashioned manual inspections
- Enables identification of machine faults and gives early warnings
- Localizes the affected components to provide information on root causes
- Prevents equipment failures and avoids unscheduled downtime
Infrared cameras
Infrared cameras are invaluable for sorting out motor problems and the condition of compressed air system motors because the infrared images they capture give you a motor’s heat signature, which reveals much about its condition.
Infrared cameras are invaluable for sorting out motor problems and the condition of compressed air system motors because the infrared images they capture give you a motor’s heat signature, which reveals much about its condition.
To develop an accurate motor heat profile, it’s vital to obtain quality infrared images when the motor is running under normal operating conditions. This provides baseline temperature measurements of motor components, including the motor itself, the shaft coupling, motor and shaft bearings and the gearbox.
Even though an infrared camera cannot see the inside of the motor, it does provide information on the exterior surface temperature, an indicator of the internal temperature. When a motor overheats, its windings deteriorate alarmingly quickly, significantly reducing the life of their insulation, even if the overheating is only temporary.
If a temperature reading in the middle of a motor housing comes up abnormally high, an infrared image of the motor can tell you if the high temperature is coming from the windings, bearings, coupling or other components.
Establishing consistent inspection routes that include thermal images of all critical motor/drive combinations and tracking to those baseline images will help you determine whether a hotspot is unusual or not and, if repairs have been done, whether they were successful.
Shock pulse monitoring
Of the methods used to assess the operating condition of rolling element bearings, shock pulse monitoring is one of the most successful and popular. Shock pulses are a special type of vibration that can be clearly distinguished from ordinary machine vibrations. A shock pulse is the pressure wave generated when one metallic object strikes another. Most of the impact momentum deforms the target object, which then oscillates at its natural frequency. This vibration ultimately dissipates primarily as heat due to internal friction material damping.
Shock pulses occur during bearing operation when a rolling element passes over an irregularity in the surface of the bearing race. Of course, there is no such thing as a perfectly smooth surface in real life. Therefore, even new bearings emit a signal of weak shock pulses in rapid succession. This carpet value rises when the lubrication film between rolling elements and their races becomes depleted.
A defect on the surface of a rolling element or bearing race produces a strong shock pulse reaction with up to 1,000 times the intensity of the carpet value. These clusters of high amplitude peaks or maximum value stand out clearly from the background noise and are ideal indicators of bearing damage.
Shock pulses propagate within a much higher frequency range than that of ordinary machine vibration, and their energy content is relatively low.
Therefore, the accelerometer used for shock pulse measurement is tuned with a 36 kHz resonance frequency that lies precisely within the shock pulse frequency range. In addition, a 36 kHz band pass filter is applied to the accelerometer signal to help filter out lower frequency mechanical vibration. When shock pulse is present the tuned accelerometer resonance is excited and amplifies the shock pulse signal, resulting in an excellent indication of bearing lubrication and damage.
Shock pulse is responsive even when far more energetic machine vibration is present. Therefore, lower frequency mechanical conditions such as unbalance, shaft misalignment or vibration from adjacent machines have little effect on shock pulse. In addition, high-frequency signals tend to dissipate rapidly so very little interference is encountered from adjacent bearings.
Instant evaluation of bearing condition is given in an easily understood green-yellow-red color scheme.
Portable dew point sensors
The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will condense to form liquid water known as dew. When this occurs via contact with a colder surface, dew will form on that surface. The dew point is affected by humidity. When there is more moisture in the air, the dew point is higher.
Operators of a compressed air system need to keep an eye on the amount of condensation produced in the system because the moisture can clog pipes, break machinery and cause contamination. In a modern paint shop system, for example, the paint pistols are typically operated by compressed air. If water condensate would mix with the paint, it would easily lead to water contamination on the paint surface. This can destroy the paint shop output of a whole day production.
Compressed air systems generally have permanently installed dewpoints instruments, but portable dewpoint instruments, such as the one below, are also used.
Portable dewpoint sensors for compressed air provide two major benefits. First, they can be used to periodically check the performance of permanently installed dewpoint instruments, which can drift from calibration. It is fast and convenient to conduct spot checks using a portable instrument. The portable instrument can easily be sent out for periodic calibration, and its calibration can in turn be transferred to the permanently installed instruments. In addition, a dewpoint instrument is invaluable for diagnosing process problems. Incorrect dewpoint levels can be an indicator that something, somewhere, has gone wrong. This may not identify or solve the underlying problem, but it is a first step in the right direction.
Contact
To learn more about vibration analysis, infrared cameras, shock pulse monitoring and portable dewpoint sensors for your compressed air system, click here to contact us. We would be more than pleased to discuss how you can effectively deploy these technologies to optimize your operations.