Speed Control I/O for Pump and Fan Motors


In order to help reduce energy use in pump and fan applications, Beckhoff Automation has announced the new KL2791 Bus Terminal for single-phase AC motor speed control. The KL2791 Bus Terminal enables direct connection of small, 1 A, single-phase motors rated 120 V, 60 Hz.

In many nations, electric motors account for more than half of the industrial electricity consumption – representing an area with enormous room for energy savings improvements. Better speed control can easily reduce excess energy use, resulting in far more cost-efficient and environmentally friendly applications. Beckhoff has expanded its Bus Terminal I/O system to help achieve this goal. Besides energy savings, improved speed control also offers noise reductions and an increase in the service life of the motor.

By using the KL2791 terminal, the energy use of capacitor, universal and shaded-pole motors can be greatly reduced. This technique is particularly suitable for drives with quadratic load characteristics such as fans and pumps. The speed controller is extremely compact and is in a standard Bus Terminal housing with a width of just 12 mm. The KL2791 Bus Terminal can be used in any of the numerous fieldbus networks supported by the Beckhoff Bus Terminal system.

The set value for the motor speed is specified by a 16-bit value. Using the KL2791, the motor is switched on and off with a practice-proven mains synchronous pattern, so that the motor consumes less power and the speed decreases significantly. This method is well suited to motors with fixed loads, such as pumps and fans, in order to achieve a setting range for the flow rate from 10 to 100 percent.


• Mains voltage 230 V AC • Rated output ≤ 200 VA • Load type 1-phase AC motors • Control type phase/full wave control • Resolution 1 % • Electrical isolation 500 Vrms (K-bus/field voltage), 3,750 V AC (1 min.) • Leakage current < 1 mA (OFF state) • Current consumption K-bus typ. 65 mA • Bit width in the process image output: 1 x 16 bit data (1 x 8 bit control/status optional) • Weight approx. 60 g • Operating/storage temperature 0…+55 °C/-25…+85 °C • Relative humidity 95 %, no condensation • Vibration/shock resistance conforms to EN 60068-2-6/EN 60068-2-27/29 • EMC immunity/emission conforms to EN 61000-6-2/EN 61000-6-4 • Protect. class/installation pos. IP 20/variable • Pluggable wiring for all KSxxxx Bus Terminals
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