Control range extended

In many applications, such as the metering of ingredients in the pharmaceutical or food industries, pumps are required that can not only be precisely controlled in terms of flow rate and delivery time, but also deliver the ingredients particularly gently. To enable the tried-and-tested pump units of the Ecodos series from Lewa GmbH to perform this demanding task even more flexibly as well as energy-efficiently in the future, the manufacturer is expanding its portfolio to include a new form of wide-range speed control (WBR).

In addition to asynchronous motors and the servo motors, permanent magnet synchronous motors, or PMSM for short, are now also being used. They are characterized by high energy efficiency and a control range greater than 1:200. This significantly expands the range of applications. The use of several pumps for different flow rates or oversizing of asynchronous motors at low speeds can be dispensed with here. Since the PMSM can be designed without a fan, it remains compact and easy to clean. The latter makes it ideal for hygienic applications. The high efficiency over the entire control range in accordance with energy efficiency class IE5+ also reduces energy costs and thus ensures a lower total cost of ownership (TCO).

Diaphragm metering pumps of the Lewa Ecodos series are particularly well suited for applications in the food or pharmaceutical industries. All materials in contact with the fluid used in the pump units meet the requirements of FDA, USP Class VI, and the EU directives for the food industry. In the hygienic version, for example, the pump head is made of PP or electropolished stainless steel with a surface roughness of < 0.5 µm. This makes it easier to clean the surfaces that come into contact with the product.

With the motor technologies used up to now, some compromises have to be accepted: "With classic asynchronous motors, whose rotor consists of a squirrel-cage rotor, the control range remains limited to 1:10 (1:50 is possible in individual cases). With encoder feedback, a significant expansion is possible," says Maurice Wirkner, Application Manager at Lewa. "In addition, the drive is relatively inefficient outside the nominal speed - especially at low speeds. This requires oversizing the drive and thus increases operating costs." Servo motors are indeed optimized for highly dynamic requirements and also cover the complete control range (1-210 pump strokes). However, they are more expensive to purchase and also require a servo inverter for control.

WBR with permanent magnet synchronous motor expands the range of applications

Lewa has now expanded its own portfolio with a drive technology that does not have these weaknesses. "Unlike the asynchronous motor, the rotor of this drive consists of permanent magnets and rotates synchronously, i.e. without load-dependent slip," Wirkner explains. "Among other things, it is characterized by its extreme control range, which often makes the use of multiple pumps for different flow rates unnecessary." Here, especially with multiple pumps, an additional manual stroke adjustment (HHV) or electric stroke adjustment (EHV) can be dispensed with and the required volume flow can be realized only by the speed control. The PMSM also has a constant torque. The complete torque can therefore be called up from motor speed 0 rpm (standstill) up to the rated speed of the motor. This ensures a particularly smooth and product-friendly start-up of the system, as each process can be started with a feed rate of 1 percent instead of the 10 percent that would otherwise be required.

There is also a high short-term overload capability, which enables drive design without oversizing for the starting torque. Thus, smaller, more cost-efficient sizes can be realized than with the classic drives. "Like the asynchronous motor, the PMSM can be controlled via a standard frequency converter, so the user can use common parts," Wirkner explains. "In contrast, with the servo motor, it would be necessary to purchase expensive servo inverters." In addition, the compact drive can be easily cleaned due to its fanless design and has a high IP protection. If required, it can also be subjected to a surface treatment with nsd tupH. The process makes the surface extremely resistant and even easier to clean. This makes it ideal for applications with high hygienic requirements, such as aroma metering in the food industry or additive admixture in the pharmaceutical sector.

IE5+ PMSM enables cost reduction as well as decentralized solutions

The only current limitation of the PMSM used is its use in non-Ex areas. "WBR using IE5+ PMSM allows us to meet the increasing demands of customers for a wider operating range and lower energy as well as overall costs," Wirkner sums up. "The topic of energy efficiency in particular is becoming increasingly important for our customers. A decentralized solution, in which the frequency converter is installed directly on the PMSM, can now also be offered with Getriebebau Nord GmbH & Co. KG, Lewa's motor partner for PMSM."