To gain the most from a maintenance strategy, maintenance must be performed under a well planned program that is tailored to the specific requirements of the equipment on-site.
Maintenance Best Practices
Typically, a site will have designated the equipment that will run to failure and which will be on a scheduled maintenance program, i.e. preventive maintenance. A successful preventive maintenance program will plan for periodic maintenance and inspections, planned major repairs, with a plan for unscheduled maintenance and stocking of sufficient spares to cover emergency breakdowns. This approach is common, however a more efficient approach is Condition-Based Maintenance (CBM) or Predictive Maintenance (PdM).
Predictive Maintenance (PdM)
The cost of technology has typically prevented many sites from implementing an effective CBM program, with most sites reserving it solely for the top 5% of critical equipment, where a return on investment is calculated with certainty. Today, technology is no longer cost-prohibitive. The top 5% of critical equipment have remained on expensive wired sensors, hardware and software packages, but the next 10-20%, typically on preventive maintenance, can now be included in the CBM program.
Commissioning, Trending and Root Cause Failure Analysis are fundamental elements to achieve increased reliability success and lower maintenance costs. By implementing CBM on more equipment, there is an increase in visibility of asset behaviour, providing for more accurate, data-driven maintenance decisions.
State Awareness Sensors
There are a number of methods available for monitoring equipment, from thermography, oil analysis and highly detailed vibration spectrum analysis (that provides Predictive Maintenance (PdM) up to 6 months in advance), to the basic overall vibration, temperature, motor current consumption and run time monitoring (providing a more later stage failure warning).
For sites that want to implement effective CBM but are limited by CAPEX budget, or establishing a return on investment can be difficult for more predictive technologies, it is viable to use a low-cost solution to demonstrate the potential value of 24/7 remote condition monitoring. Basic sensors can be used to monitor multiple equipment parameters, and then develop correlations within the data over time to establish alerts and shut-off limits to prevent catastrophic failure.
The easiest and most flexible method for monitoring equipment health is via online remote monitoring of wireless sensors.
Inside the vibration of machinery is the frequency and amplitude of velocity and acceleration. High quality sensor systems allow for the inspection of all vibration elements providing detailed and very early stage warnings of failure and accurate failure analysis. When all of these vibration elements are combined, it is called a time waveform and the output value is commonly referred to as RMS and is measured in mm/s.
RMS or Root Mean Square, is the square root of the average of the squared values of the waveform, and must be used in all calculations regarding energy and power in a waveform.
As machinery health declines, the level of overall vibration often increases. It is this fact that can be used to observe the health trends of equipment across an entire plant, and remote monitoring using an online system means you can view status instantaneously from any computer or mobile device. There are some instances where change in vibration is not necessarily indicative of machine health (VSD/VFD’s for example), and including temperature and motor power current sensors in the equipment monitoring program can cost-effectively expand the visibility of equipment health for failure analysis. This method of condition monitoring is not predictive, but is a good entry into condition monitoring.
4-20mA Sensors and MODBUS
A common method for sensors to communicate to a PLC and SCADA/DCS/BMS system is via a change in electrical current from the sensor to the receiver. A value is set against 4mA and another at 20mA. For example, a vibration sensor with a maximum of 25mm/s would have 0mm/s set at 4mA and 25mm/s at 20mA. This change is identified by the PLC/SCADA/DCS/BMS system and programmed actions take place at certain mA levels. The benefit to this generic method of communication, is that almost anything you want to monitor already has a product out there with this output type. However, those systems are wired, and typically require significant investment of budget, IT infrastructure, and human resources or contractors/consultants to manage them.
A wireless 4-20mA sensor system offers significant flexibility and price advantages. The system receives the current output of an industry standard 4-20mA output sensor, of any type, and transmits that data to the cloud. This can be used to log data from existing site sensors, or to monitor data from sensor types that are not available in a wireless range. To further extend on the functionality, there is also a wireless receiver that sends data from the cloud which is then transferred to a PLC/SCADA/DCS/BMS via standard MODBUS wired connection.
Wireless condition monitoring technology can enhance the visibility of equipment health more than ever before, and at affordable pricing that makes it easy to justify in CAPEX requests.