One thing is a given – for battery-powered vibration sensors, the more you use them, the quicker the battery energy stored is depleted.
Many are excited about the easy installation benefits of battery-powered vibration sensors but overlook the following key points when considering battery-powered vibration monitoring versus traditional hard-wired or semi-wired (tethered) monitoring:
- Battery compromises on performance
- Labor and manual effort over time
- Extreme temperatures
- Number of axis monitored
- Monitor or protection?
Check out this LinkedIn message we got from a prospective customer who was using battery-operated vibration sensors:
For battery powered wireless vibration sensors to operate for years there are usually some sacrifices in performance and/or operation time.
- To extend battery life, some sensors are designed to periodically operate in sleep mode, where the sensor shuts down all operations except the internal clock. Other sensors are designed to collect data continuously and periodically shutdown their wireless broadcasting functions to extend battery life. Unexpected changes in operating condition such as a pump running dry or a compressor pressure fluctuation and other catastrophic machine failures could be missed during sleep periods.
- Sampling rate is also a consideration for extending battery life. Less samples per second means more battery life, because a less powerful and slower microprocessor consumes less power. Less samples per second translates into less resolution in the vibration data, which may result in a missed diagnosis or an unplanned failure, especially for fast speed machines.
- Sampling duration is typically limited to extend battery life. This also translates to less resolution for slower speed machines, which require longer sample times to get more revolutions of the machine in the sample. In other words, a machine rotating at 3600 RPM requires a short sample duration, but a machine rotating at 120 RPM requires a longer sampling duration to collect enough revolutions in the sample to achieve the required resolution to make an assessment of the machine’s condition.
- To minimize power consumption, battery-operated vibration sensors typically have a “one-size-fits-all” sensing element with a wide acceleration range (+/- 20g) to cover most of the possibilities and a minimum frequency response range (10Hz – 1kHz). This makes them unsuitable for slow machines where failure modes exhibit low vibration levels from 1Hz to 5Hz and unsuitable for very fast rotating components, like rolling element bearings and gearboxes where failure modes exhibit vibration levels above >5kHz.
- Battery consumption is sometimes adversely affected by excessive wireless communication due to connection failures, communication retries, and interference. These issues may not be apparent during sensor installation and occur due to unpredictable weather conditions, personnel movement, mobile vehicles, temporary structures or factory product movement obstructing the “line of sight” communication path.
Labor and Manual Effort
Some battery-operated sensors have a wireless solution called Bluetooth (a short range communication protocol).
In this case, personnel may be in harm’s way going on routes to periodically collect the vibration data via handheld Bluetooth data collector devices.
This approach does not have the benefits of online solutions where the sampling interval is more frequent than weekly or monthly.
Don’t put your team in harm’s way.
Another challenge and consideration is an extreme cold or hot operating temperature. Extreme operating temperatures deplete battery life faster and can damage the battery.
Typical motor bearing operating temperature is +60° C to +71° C (+140° F to +160° F) but can range from +100° F to +160° F.
Pump bearing range is also around +60°C to +71°C (+140° F to +160° F), but can be much higher depending on the process temperature.
Gear drive bearing temperature range is (+160° F to +180° F). Fans often move hot air, so fans are often subjected to higher bearing temperatures.
Most battery-powered vibration sensors are limited, on the high end, to +70° C (+160° F) and at the low end to -20° C (-12° F) for operating temperature.
Number of Axis Monitored
Vibration is multi-dimensional, as all machines move in the X, Y and Z axis. If you use a single axis vibration sensor, you only see one plane of the machine vibration data. A machine problem may be missed or detected very late in the failure mode.
Monitoring or Protection?
Battery-powered vibration sensors are periodic machine monitoring devices.
Machine protection includes real-time or near-real-time monitoring that automatically alarms and initiates the shutdown of the machine.
Battery-powered vibration sensors are NOT intended to be used as protection devices. When the battery-powered vibration sensor alarms due to a high vibration, an investigation and corrective action are required to save the machine.
Battery-powered vibration sensors are NOT intended to be used as machine protection devices.
Investigations indicate the time lag between alarm notification, a person investigating the data provided by the battery-powered vibration sensor, and manually initiating the shutdown action or implementing corrective actions. This is the difference between a saved machine and a catastrophic failure.
Wired vibration sensors connected to a PLC or a DCS for automatic machine protection should be considered if the machines or process uptime are important to your success.
Where does the system intelligence reside?
Battery-powered vibration sensors are not stand-alone devices.
Typically a battery-powered vibration sensor system includes battery-powered devices, wireless receivers (Access Points), and software that resides locally on a computer or in a cloud based device management and dashboard system.
Most of the “smarts” like alarming, notification, filters, and calculations are in the software.
Battery-powered vibration sensors are not stand-alone devices.
Consider systems that monitor continuously and then automatically notify you when there is an exception. Wired or semi-wired (tethered) vibration sensors tend to have more intelligence within the sensor due to constant power available for more advanced firmware processing.
Having the intelligence within the sensor allows for more capabilities that are not possible in a battery-powered sensor, such as:
- Real-time machine protection;
- Real-time integration with PLC/DCS for correlation with other process variables; and
- High pass, low pass to remove unwanted process noise or frequencies not associated with fault frequencies.
- Bandpass filtering to focus on specific machine fault frequencies
- Unique algorithms that deal with bearing faults such as mechanical looseness (impact), enveloping or kurtosis technologies.
Battery-powered vibration sensors require more maintenance overhead than other types.
Battery-powered sensors have additional maintenance overhead that is not required for wired or semi-wired (tethered) sensors. Specifically:
- Battery Replacement – If you had 100 simple machines (pump/motor sets) with a battery powered vibration sensor on each bearing (assume 4 bearings per machine), if the expected battery life is three years, you would need to change about one battery (on average) every 3 days. The cost of the battery is a minor consideration, but the time required to install the replacement battery and the dispose of the old one are the more costly part of maintaining a battery-powered sensor system. The time required to replace a sensor depends on the accessibility to the sensor location. A few examples of sensors that are difficult to access are a cooling tower gearbox or the pillow block bearing on a baghouse fan.
- Calibration – periodically most vibration sensors must have their calibration verified. Usually it is on an annual basis, but that depends on the criticality of the machines or the process. Traditionally, a portable vibration shaker with a reference “gold standard” vibration sensor is used to verify the accuracy of the installed battery-powered vibration sensors. It could be more difficult and time consuming to verify the calibration of a wireless battery powered vibration sensor depending on the update and broadcast interval.
- Local Indication – Many battery-powered vibration sensors do not have any LED indicator for power, faults, or alarm conditions (to reduce power consumption). The operator cannot look at the vibration sensor to see if it is on or working properly. Instead, they must rely on wireless remote access or they must communicate with another person to confirm sensor health, which takes more time.
- Battery Disposal – Some batteries are considered hazardous waste and contain toxic materials. In the USA, a Lithium-Ion battery is considered non-toxic, but it does contain hazardous materials that have negative effects on our health and the environment if not recycled or disposed of properly.
Protect Your Machines with the VTB-TriVibe Vibration Sensor
The trade-off between the wired and battery-operated solutions are many. Find out how Machine Saver’s TriVibe is winning innovation awards and how TriVibe overcomes the challenges above. Find out why Machine Saver is the fastest-growing remote machine monitoring and machine protection company in the world!
Choosing Battery-Powered Vibration Sensors | Machine Saver, Inc. – Houston, TX