Condition monitoring with intelligent drives

In the transition to the current millennium, we have witnessed a profound change in technology, which has led to a whole new way of working in a digital world. This is the fourth industrial revolution. The first industrial revolution, which occurred during the 18th and 19th century, was a mechanical revolution, triggered by the invention of the steam engine. By the end of the 19th and early 20th century, the second industrial revolution unfolded with the adoption of mass production, electrification, and changes in communication. This period is also referred to as the Electrical Revolution. Later in the 20th century, the third industrial revolution brought advances in semiconductors, computing, automation and the internet. This phase is also known as the Digital Revolution.

The fourth industrial revolution has emerged as a result of networking computers, people, and devices fueled by data and machine learning. Although the term “Industry 4.0” is quite vague, a possible definition for Industry 4.0 describes the intelligent networking of people, devices, and systems by utilizing all possibilities of digitalization across the entire value chain.

The impact of Industry 4.0 on motor systems and building management systems is a migration from the “automation pyramid” to “networked systems”. This means that the various elements of the system, such as motors, drives, sensors and controls, are interconnected and connected to a cloud - a data center where data is stored, processed, analyzed, and decisions are made.

In an automation network, the amount of data is prominent. As data is mainly produced by sensors, the number of sensors in modern automation systems is increasing. Motors and driven machines such as fans, pumps and conveyors are not the most obvious participants in a data network. Sensors are therefore required to collect data from these machines. The sensors are connected to the data network using various means to utilize the data. During the introduction of an advanced condition monitoring system, the additional cost of sensors and connectivity is often seen as a barrier.

Modern variable speed drives open new opportunities in the Industry 4.0 automation network and in building management systems. Traditionally, drives have been considered power processors for controlling the motor, fan, conveyor and/or pump speed. Today, drives are also part of the information chain, using the advantage of built-in processing power, storage capacity, and communication interface, within the drive.

The following are different kinds of maintenance strategies:

• Corrective maintenance: The product is exchanged after a fault.
• Preventive maintenance: The product is exchanged before a fault, although no notifications are received from the product.
• Condition-based maintenance: The product provides a warning when the actual lifetime of the product varies from the expected lifetime and possible root causes are indicated.
• Predictive maintenance: The product provides a warning before the product reaches the designed hours of operation, in order to initiate service action.

Corrective and preventive maintenance are fault (event) or time-based. Therefore, maintenance is performed in case of fault(s) (corrective) or after pre-established operation hours (preventive). These types of maintenance do not use any feedback from the actual application.

With the introduction of Industry 4.0 and the availability of sensor data, condition-based and predictive maintenance is now possible. Such maintenance strategies use actual sensor data to determine the condition of the equipment in service (condition-based maintenance) or to predict future failures (predictive maintenance).

Condition-based maintenance is the easiest and most intuitive maintenance technique based on data from the actual application. The data acquired is used to monitor the health of the equipment in service. For this purpose, key parameters are selected as indicators to identify developing faults. The condition of a piece of equipment typically degrades overtime. This is illustrated by the P-f curve which shows a typical degradation pattern. Functional failure occurs when the equipment fails to perform the intended function. The idea of condition-based maintenance is to detect the potential failure before an actual failure occurs.

Advantages of planning maintenance actions

• Downtime reduction
• Elimination of unexpected production stops
• Maintenance optimization
• Reduction in spare part stock inventory

An integral part of condition-based maintenance involves monitoring the condition of the equipment. In variable speed applications, the condition of the application often depends on speed. For example, vibration levels tend to get higher at higher speeds, although this relationship is not linear. Indeed, resonances can occur at certain speeds and then disappear when the speed is increased.

Using an independent system to monitor the condition of a variable speed application is complicated by the need for knowing the speed and the correlating monitored value with speed. Using drives for condition monitoring (“drive as a sensor” or “drive as a sensor hub”) is an advantageous solution, as the information about application speed is already present in the drive. Additionally, information about the load/motor torque and acceleration is readily available in the drive.

Learn more in the CBM white paper and video

Today, drives are more than simple power processors. With the ability to act as sensors and sensor hubs, to process, store and analyze data, along with connectivity capabilities, drives are vital elements in modern automation systems.

Drives are often already present in automation installations and therefore present a great opportunity to upgrade to Industry 4.0.

This enables new ways of performing maintenance, such as condition-based maintenance. The functions are already available in some drives and early adopters have already started using the drive as a sensor.

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