Showing posts from August, 2015

What can a PLC do? Why do we use them?

The meaning of PLC… “PLC” means “Programmable Logic Controller”, that’s clear. The word “Programmable” differentiates it from the conventional hard-wired relay logic. It can be easily programmed or changed as per the application’s requirement. The PLC also surpassed the hazard of changing the wiring. The PLC as a unit consists of a processor to execute the control action on the field data provided by input and output modules. In a programming device, the PLC control logic is first developed and then transferred to the PLC. So, what can a PLC actually do? It can perform relay-switching tasks.It can conduct counting, calculation and comparison of analog process values.It offers flexibility to modify the control logic, whenever required, in the shortest time.It responds to the changes in process parameters within fractions of seconds.It improves the overall control system reliability.It is cost effective for controlling complex systems.It trouble-shoots more simply and more quicklyIt can …

Comparison of Soft Starting and Frequency Converter Motor Starting

Soft starting A soft starter is, as you would expect, a device which ensures a soft starting of a motor. A soft starter has different characteristics to the other starting methods. It has thyristors in the main circuit, and the motor voltage is regulated with a printed circuit board. The soft starter makes use of the fact that when the motor voltage is low during start, the starting current and starting torque is also low. Motor soft starter Advantages // Soft starters are based on semiconductors. Via a power circuit and a control circuit, these semi-conductors reduce the initial motor voltage. This results in lower motor torque. During the starting process, the soft starter gradually increases the motor voltage, thereby allowing the motor to accelerate the load to rated speed without causing high torque or current peaks. Soft-starting curve – Synchronous speed – Full load torque (left) and Full load current (right)
Soft starters can also be used to control how processes are stopped. S…

PLC Implementation Of Forward/Reverse Motor Circuit With Interlocking

Forward/Reverse Motor Interlocking Figure 1 illustrates a hardwired forward/reverse motor circuit with electrical and push buttoninterlockings. Figure 2 shows the simplified wiring diagram for this motor. The PLC implementation of this circuit should include the use of the overload contacts to monitor the occurrence of an overload condition. The auxiliary starter contacts (M1 and M2) are not required in the PLC program because the sealing circuits can be programmed using the internal contacts from the motor outputs. Figure 1 – Hardwired forward/reverse motor circuit
Low-voltage protection can be implemented using the overload contact input so that, if an overload occurs, the motor circuit will turn off. However, after the overload condition passes, the operator must push the forward or reverse push button again to restart the motor. Figure 2 – Forward/reverse motor wiring diagram
For simplicity, the PLC implementation of the circuit in Figure 1 includes all of the elements in the hardw…