Distributed frequency inverters with Safe Stop functionality

SK 200E inverter series from NORD provides certified safety technology for applications up to SIL3

Operator safety is essential on the shop floor at all times. When a safety circuit is activated because a safety cover or door has been opened, any danger of accidents through rotating machine parts must be ruled out. On the other hand, high availability of machines is vital. Economic efficiency requires quick restarts after safety-related shutdowns. SK 200E distributed frequency inverters from NORD DRIVESYSTEMS, though optimized for cost-efficient drive solutions, feature several safety functions which, depending on the switching device, enable safe shutdown procedures in high risk applications that comply with Category 4 or Performance Level e according to EN 13849-1.

Illustration: Combining cost-efficiency and safety: NORD’s SK 200E series of distributed frequency inverters

Conventional frequency inverters in this performance class prevent motors from restarting by disconnecting the voltage supply or the 24 V control supply. By contrast, SK 21xE and SK 23xE models feature a certified safe pulse blocking device as well as digital inputs for the “Disable Voltage” and “Quick Stop” functions. These enable Stop Category 1 (controlled motor braking in line with SIL1), followed by Safe Torque Off (SIL3-compliant) or Stop Category 0 (SIL3-compliant) according to EN 60204-1. Since the voltage supply is blocked without switching off the control or power electronics, the units remain on standby and are ready to be switched on without re-initialization after the safety circuit is closed. In addition to high availability, the inverters’ safety technology provides more economic benefits: contactor components are not required, and since the safety functions are activated electronically, there is no need for regular maintenance or exchange of electromechanical contacts. separately on the machine frame or other equipment. Alternatively, they are available as internal modules that extend the integrated functional range without altering the dimensions of the inverter. Due to the integrated proprietary system bus, up to four SK 200E frequency inverters can be connected to the higher level bus system via a single technology unit. The system bus tunnels the parameter data, making all the participants’ data sets available at every RS232 interface on the connected inverters and the technology unit. NORD supplies the distributed SK 200E inverters, which are designed for mounting on the motor terminal box, in sizes 1 to 4 with outputs between 0.25 and 22 kW. Different variants, various performance grades, and a range of upgrade options enable cost-efficient and customized drive solutions for any distributed application from fan or pump operation all the way to complex positioning tasks.