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17 January, 2021

Making sense of the torque

23 June, 2020

Variable-speed drives (VSDs) are intelligent devices, acting like virtual sensors by continuously measuring and calculating parameters that can affect an application. ABB’s Martin Richardson suggests that, if used correctly, this could shift industry from a “fix it when it breaks” mentality to “fix it before it breaks”.

VSDs accumulate vast amounts of data, often without needing any external sensors. Using this data intelligently, either locally or in the cloud, can have a significant impact, not just on the condition of the VSD, but also on the application. Yet this ability for VSDs to use their internal mathematical models and calculations as virtual sensors is often under-valued or overlooked entirely.

VSDs continuously track parameters such as torque, current, power and temperature. Take, for example, torque measurement. This normally requires a separate sensor such as a torque transducer. However, knowing the status of torque is a fundamental calculation at the heart of any VSD operating platform. Torque opens up many smart ways to use the drive – from detecting blockages to determining the thickness of sludge.

An industrial mixer, for example, can use torque to represent the consistency required of the mixture. When the mixer reaches this value, it triggers a stop to the mixing process, thus enhancing the consistency of the end-product. When used alongside motor speed and flow measurements, torque can indicate any drop-off in efficiency levels or even potential design flaws in pumping systems.

Torque is also a powerful tool in the quest to monitor the condition of key assets. In one simple real-life example, an Archimedes screw was being used on the inlet works at a wastewater site. The Scada system monitoring the application detected that the VSD and the motor were running and, because there were no motion sensors on the screw, it assumed that the Archimedes screw was functioning. The reality was that the V-belt driving the screw had broken. To combat this oversight, a condition-monitoring load curve was set-up within the VSD. Now, if the torque falls below a pre-defined value, this indicates a belt failure and trips the drive, alerting the operators that there is a problem.

In another case, engineers monitoring the data from two mirror-image wash-water pumps, recorded their flow, torque and speed using the VSD. By plotting basic data, the engineers noticed that, even though they were running at the same flow rate, one pump was 15% more efficient than the other. A decision was made to prioritise the more efficient pump.

Today there are many parameters that are measured or calculated within VSDs. Each parameter generates hundreds of bits of useful data that can help identify broken cooling fans, high ambient temperatures, loss of an analogue signal, excessive torque levels, or motor cooling issues. A VSD no longer simply turns a motor: it has an intelligence, flexibility and adaptability that can change the way that an entire plant is looked after.

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