Practical Tips on Predictive Maintenance

April 30, 2015
Automation vendors offer advice about the best ways to go about predicting impending equipment malfunctions.

Henry Menke, marketing manager, position sensors, Balluff

One of the best ways to predict impending equipment malfunctions is to establish a database of performance metrics to delineate the boundaries of “normal” operation. Through subsequent and ongoing performance monitoring and recording, small changes in performance that occur over time can be detected and investigated before there is a downtime event.

Consider a valve actuated by a hydraulic cylinder. Any number of failure modes can befall such a valve, particularly if it operates more or less in a static position most of the time. If it is ever called upon to change position, it may unexpectedly fail to respond.

To address this concern—particularly for mission-critical values or safety-related valves—a linear position sensor is installed to monitor the movement of the cylinder. These sensors deliver continuous position information in analog or digital form. By routinely exercising the valve as part of a proactive maintenance program, the valve’s motion profile can be recording to track things like speed and degree of movement.

When the valve’s speed is found to slow down below a defined threshold, for example, it could be an indication of low hydraulic pressure, a hydraulic leak, a sticking mechanism, or corrosion or blockage in the valve itself. These issues can often be detected in their incipient stages, before they become catastrophic failures.

Analog and digital pressure sensors on the hydraulic lines supplying the valve actuator provide another channel of predictive maintenance information. In combination with the position sensor, comparison of measured pressure data to historical norms can reveal even more information about the operational readiness of the valve.

Clinton Hommel, product marketing specialist, energy monitoring and management, Phoenix Contact

The availability of information now makes many things possible, such as monitoring the power a facility uses at the utility connection. This tells facility operators how much power has been consumed, but it doesn’t provide details on where or how it’s being used within the facility. So knowing how energy is consumed by providing granular detail often provides the operation with a unique insight to a particular machine’s usage patterns and how it can be optimized to reduce consumption.

Using energy monitoring information for more than utility bill reduction makes it possible to be proactive on machine maintenance. One example is an electronic motor management module that turns an ordinary motor into a complex sensor. Customers are using the feedback they get from individual motors to identify all kinds of issues before they escalate to full-blown problems.

This information allows them to be proactive on motor rebuilds because they can spot a failing winding or excessive bearing draw before a failure occurs. They can also spot issues on pumping applications, such as clogged filters or dry running, before an unexpected filter-cleaning shutdown is required or before air cavitation damage occurs.

This is made possible only by analyzing the energy usage profile of individual pumps. This information also allows them to optimize motor sizes and production line operations based on overload or underload conditions detected on the motor during normal operation.

Smart instrumentation, especially in motor-intensive applications, is becoming an invaluable tool for identifying issues before there is a serious problem. It enables operators to implement successful proactive maintenance programs that are cost-effective and produce real results.

Tracy Doane-Weideman, marketing manager, analytics, Endress+Hauser

The Memosens digital protocol enables complete galvanic isolation of a digital sensor and eliminates the cable and transmitters as an influence on the performance and perceived health of a sensor. Better data leads to better and more proactive maintenance decisions to protect against failure, reducing labor costs and increasing plant uptime, reliability and profitability.

In certain critical processes, the pH value is crucial in properly controlling electrolysis. Memosens sensor technology can enhance pH measurements and substantially cut costs for chemical companies. One company was having trouble with analog pH measuring points because of the high impedance resistant signals that are susceptible to faults and malfunctions, resulting in high maintenance expenses and low reliability and availability.

By fitting all measuring loops with digital Memosens technology, the company gained a common platform for sensor data and the measured value was converted directly to digital signals inside the sensor. Since the sensors use inductive coupling, both for the signal transmission and power supply, this tackled the major problem of pH measurements at its roots. Memosens sensor electronics can be pre-calibrated in the lab under ideal conditions, so a sensor can be exchanged quickly and easily on site.

These smart sensors constantly deliver information on their state, so that probes are replaced only if necessary or cleaned and regenerated in the lab where possible. This predictive maintenance even increased safety by reducing the time personnel spent in the field. It triggered a continuous improvement process where all measuring points were gradually retrofitted with WirelessHART technology, allowing the facility to centrally analyze all sensor status information.

Read more about how Smart Instruments Power Evolution to Predictive Maintenance.

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