Wireless Sensor Maintenance
Alan Friedman Cat IV, CRL, CMRP, Author
Vibration Analysis Training and Certification
In a recent LinkedIN poll, I asked how much life people were getting from their wireless accelerometer batteries. As you can see from the results below, 43% of of users reported getting less than 2 years of battery life. If you have 1,000+ battery powered sensors in your plant, maintaining them and changing them every two years will be quite a task!
There were no caveats to this question. I did not ask how frequently data was being collected and sent out. I also didn't ask about the types of data being measured and transmitted. Both of these would have a large effect on battery life. I simply wanted to get an idea of what sort of battery life people were getting when using the sensors as they are using them now.
What Else Needs to Be Maintained?
Often times wireless vibration sensors are sold as turn-key systems with remote analysis services. You just slap the sensor on the machines and everything else is taken care of. The question is: Is this true?
What if you remove a damaged sensor from a machine and replace it with a new sensor but you don't inform the company that is managing the system? That's obviously going to cause a problem! They obviously have to know which sensors are mounted where.
Many of the wireless sensors are triaxial or bi axial. What this means is that the sensor orientation matters. If you take the sensor off for one reason or other and put it back on again, it needs to be oriented the same way. Otherwise, you are comparing apples to oranges.
Sensors have to be mounted correctly and firmly to the machine. I had an end user complain to me once that the sensors kept falling off a machine. He was going to cancel his contract with the company providing the sensors and remote monitoring services in favor of a new company. It didn't occur to him that this would still require sensors to be mounted firmly to the machine! This problem was clearly not the responsibility of the service company.
Gateways and Network Nodes Etc
There are a variety of different communication protocols for wireless sensors. Some use Bluetooth, others 3g - 5g cell, others use WiFi etc. These communication networks also need to be maintained. This may or may not be the responsibility of the vendor. It depends on the system.
Machine Information
Some of the new systems on the market are just taking simple, single value vibration readings such as RMS, Pk or Pk-Pk Velocity and or Acceleration. Baselines are automatically generated after the sensors have been installed on the operating machinery for a few weeks. Future readings are compared against these baselines and alarms are generated. This is great and works fine, but it is limited in scope. It will not tell you what problem the machine has.
If you want to do diagnostics, for example, differentiate between unbalance, misalignment, bearing wear, gearbox problems etc. Then you need to provide your vendor with detailed information about the machine. In short, we don't want to diagnose rolling element bearing wear in a machine with sleave bearings or cavitation in a motor. We need to know where the data came from in order to know what faults the equipment can have.
Machine History
It is also helpful if you have a feedback system with your provider to let them know if machines have been repaired or replaced. What is a remote analyst supposed to conclude if the vibration levels on a machine suddenly get lower and stay lower? Is there a problem or did the machine get overhauled?
Some Tips
Feedback
This technology is still relatively new. I'd be interested in hearing about your experiences and tricks and tips you've discovered to help make the technology successful. I'd appreciate your feedback in the comments section.
If you are interested in vibration analysis and would like to learn more, why don't you...
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