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Installing sensors in the control cabinet: when does this add value?

A growing number of companies are moving toward condition-based maintenance (CBM) on assets such as motors and pumps.  This concept is based on the idea of matching maintenance to the state of the equipment, rather than time-based preventive maintenance tasks.  When the maintenance manager has insight into the real-time condition of a machine, he can adjust his maintenance strategy optimally.

Sensors collect data, which is used to determine the condition of the connected assets. For example, velocity sensors and accelerometers measure mechanical vibration; acoustic sensors measure air pressure; thermal senors measure infrared radiation. For each application there are several commercially available sensor options—some more robust and accurate than others. There’s one drawback common to all these kinds of sensors, however: they must be physically mounted on or near the machine to take measurements. That isn’t always easy to do—consider underground drainage pumps or conveyors that transport molten steel.

Fortunately, there’s a way to accurately determine a machine’s condition from afar: by measuring the current and voltage drawn by the motor that drives it. Deviations in the power supply can indicate a mechanical or electrical problem in the asset itself. For example, vibrations disrupt the electromagnetic field, which translates to changes in the current sine wave. Every mechanical and electrical failure mode has a specific signature or fingerprint that can be measured in the current or voltage.

This method of data collection also serves the goal of condition monitoring. The difference with other traditional methods is where the measurement takes place. Current and voltage sensors don’t need to be placed on or near the asset; they just need to be somewhere on the cables between the power supply and the machine. Typically, these sensors are installed in the motor control cabinet. Installing sensor modules in a control cabinet (rather than in the field) can provide many advantages.

Field sensors are subject to environmental factors

Sensors in the field are subject to local conditions. In the food sector, for example, strict hygiene and quality requirements apply. Rooms, surfaces and materials are cleaned often. Equipment and the sensors attached to it must be resistant to water and high humidity.

In other sectors, external factors such as extreme temperatures, pressure or contaminants may be present. Sensors must be sufficiently robust to withstand these conditions—a defective sensor doesn’t provide reliable data. The motor control cabinet, in contrast, is a stable, temperate, dry room—ideal conditions for sensors to do their job.

Field sensors need remote energy sources

To collect and send information, sensors must be provided with an energy source. In the past, this required the laying of power cables, a time-consuming and expensive affair. In recent years, wireless sensors have gained significant ground. These sensors usually run on batteries. How fast that battery runs out depends on the type of sensor and the application. Sending data once a day or every fifty milliseconds makes a big difference. Once the batteries are drained, a mechanic will have to replace them: no battery, no data.

One solution to this problem is energy harvesting, a process in which a source of energy (for example, heat) is extracted from the immediate environment to power the sensor. Unfortunately, it’s not yet a solution that works with all sensors or in all situations. With sensor modules placed in a control cabinet, the energy problem disappears. Just hook the sensor up to the main power supply.

Field sensors cost more to install

A third advantage of sensor modules that install in a control cabinet is cost. The assets whose condition needs to be monitored are often spread over a facility. In an airport baggage handling system, for example, the distance between the motors that drive a conveyor belt can be enormous. It would take quite a long time to install sensors on each individual motor.

Moreover, there’s a real art to installing proximity-based sensors at just the right place on the asset. Some sensors must be located very close to the expected source of vibration or sound, while others must be installed in places that are difficult to reach. It can prove quite problematic to reach motors integrated into larger machines, for example, or submerged pumps.

Some locations add safety risks that drive up the cost of installation. Sensors installed in hazardous areas must be certified for use in (for example) ATEX zones or flammable environments. The installation itself also requires extra precautions that can range from hazmat suits to certified divers. All this makes proximity-based sensors cumbersome and expensive to install.

All these issues disappear once you can install a sensor in the motor control cabinet. By design, the motor control cabinet is placed in a non-hazardous area that is easily accessible. What’s more, the motor control cabinet brings the power supply for several assets together in one central location. That drives down the cost of sensor installation even further.

In practice

SAM4 is a current- and voltage-based condition monitoring system from Semiotic Labs. Several companies have already chosen SAM4 because its condition monitoring sensors install in the motor control cabinet and not on the asset itself.  Two examples are Vopak Vlaardingen, an industrial storage company, and Kaak Group, a manufacturer of machines for the bakery industry.

Vopak Vlaardingen

“We temporarily store products from seagoing vessels in storage tanks,” says Marcel Kool, a maintenance engineer at Vopak. “The product is then further distributed using trucks or lighter barges. About two hundred pumps handle the loading at our Vlaardingen location. For us, it’s important to monitor our equipment better so that we can improve our service to our customers. We want to increase the predictability of maintenance.”

Vopak Vlaardingen chose not to install sensors on the pumps themselves, but centrally in a motor control cabinet.  “The pumps aren’t positioned far from each other, but they are insulated so you can’t reach them directly if you want to install a sensor,” says Kool. “ATEX wasn’t an issue at our location, but it would be an extra factor to take into account at other locations.”

Installation & baseline determination

Vopak started a pilot program on ten pumps.  “The installation of the sensor modules in the control cabinet went quite smoothly,” Kool says. “No special procedures were required, which was a huge advantage. After the modules were installed, there was a period in which the machine-learning software constructed a baseline for the pump, a sort of starting position.

“Almost immediately after this phase, we received two alerts based on the data. The online dashboard indicated that each pump was almost failing. Our mechanics examined these two pumps in the field, and what they found corresponded with what the system indicated. That increased our confidence in the system, which certainly offers perspective for the future.”

Even so, it may not make sense to extend the system to all 200 pumps at the Vlaardingen site. “The pumps we selected for the pilot run regularly,” says Kool. “We also have a small number of pumps on site that we only use sporadically. These pumps would take a little longer to learn, simply because they’re used so little. If we run a business case on these pumps, the outcome may be that it’s not sufficiently profitable to monitor them, period, whatever sensor technology you choose. But for the majority of our pumps, condition monitoring is an option to consider.”

Kaak Group

Kaak Group has added SAM4 to the integrated asset monitoring options they offer to customers. “The bakery lines our customers use combine a number of machines,” says Marcel Trapman. Trapman is a team leader at Kaak’s iBakeWare division, which builds software to monitor and analyze bakery production lines and the baking process. “There are critical, large motors in these lines that are built to customer specifications. If one of these motors breaks down, the line has to be stopped, endangering the bakery’s ability to deliver. To avoid a long standstill, the bakery has to stock spare motors. By using sensors to monitor the motors’ condition, they no longer need this safety stock. If a developing fault is found, there’s enough time to inspect the motor, order spare parts and schedule maintenance.”

Kaak Group’s bakery lines already contain many different types of sensors, and can be equipped with optional sensors at the customer’s request. An example of such an optional sensor is Semiotic Labs’ SAM4.

“At a later stage we want to be able to give the customer the option to monitor the system’s motors using data and sensors,” Trapman says. “For us, therefore, the possibility of retrofitting sensors in a fairly simple manner is of great importance. With the sensor module in the control cabinet, we don’t need to reach the motor at all. We therefore see it as added value for the customer to be able to retrofit it fairly easily. That’s why we chose this type of system.”

Would you like to know whether sensors in the motor control cabinet also have added value for you? Check out our solution, follow us on LinkedIn or schedule an appointment with us.

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