The system consists of a submersible pump controlled by a Danfoss VLT AQUA Drive and a pressure transmitter. The transmitter gives a 4-20 mA feedback signal to the VLT AQUA Drive, which keeps a constant pressure by controlling the speed of the pump. To design a drive for a submersible pump application, there are a …
How to select AC converter for VSD?
Altough manufacturers’ catalogues try to make it easy as possible, there are many variables associated with the selection and rating of the optimum electric motor and AC converter for a Variable Speed Drive (VSD) application. In many cases, it requires considerable expirience to get the selection right. The reason why it is difficult is because …
Ladder Diagrams And The PLC
The ladder diagram has and continues to be the traditional way of representing electrical sequences of operations. These diagrams represent the interconnection of field devices in such a way that the activation, or turning ON, of one device will turn ON another device according to a predetermined sequence of events. Figure 1 illustrates a simple …
PROFIBUS at a Glance
PROFIBUS is an open, digital communication system with a wide range of applications, particularly in the fields of factory and process automation. PROFIBUS is suitable for both fast, time-critical applications and complex communication tasks. PROFIBUS communication is anchored in the international standards IEC 61158 and IEC 61784. The application and engineering aspects are specified in …
When we started to use PLCs after all?
PLCs (Programmable Logic Controllers)were first introduced in the 1960’s. The primary reason for designing such a device was eliminating the large cost involved in replacing the complicated relay based machine control systems. Bedford Associates (Bedford, MA) proposed something called a Modular Digital Controller (MODICON) to a major US car manufacturer. The MODICON 084 brought the …
Typical servo motors data – ABB
Torque constant The torque constant is an important measure given to the synchronous servo motor. It is expressed as Nm/A and determines how much torque is produced per ampere. Back EMF The permanent magnet motor acts like generator and builds up back EMF voltage which is related to angular speed. Back EMF is opposite to …
How Stuxnet (PLC virus) spreads – Part 4
Continued from How Stuxnet (PLC virus) spreads – Part 3 » Read here Propagation to other Perimeter Network Computers Once the worm has a foothold in the Perimeter Network, it would attempt to infect any print servers and file servers it could discover. Next, the worm would identify the WinCC software installed on the Web …
How Stuxnet (PLC virus) spreads – Part 3
Continued from How Stuxnet (PLC virus) spreads – Part 2 » Read here Compromising the Network Given the well-secured industrial control system described above, how could a worm like Stuxnet ever penetrate all the way to the PLCs? Yet clearly it did – Siemens reports that it is aware of at least 22 sites that experienced …
AC motors – Protection against short circuits
Every electric motor has operating limits. Overshooting these limits will eventually destroy it and the systems it drives, the immediate effect being operating shutdown and losses. A short circuit is a direct contact between two points of different electric potential: – Alternating current: phase-to-phase contact, phase-to-neutral contact, phase-to-ground contact or contact between windings in a …
How Stuxnet (PLC virus) spreads – Part 2
Continued from How Stuxnet (PLC virus) spreads – Part 1 » Read here Stuxnet is a computer worm designed to infect Siemens SIMATIC WinCC and S7 PLC products, either installed as part of a PCS 7 system, or operating on their own. It starts by taking advantage of vulnerabilities in the Windows operating systems and …
