Mutchus

    While connecting field devices to Programmable Logic Controllers we always get confused about sinking and sourcing operations. Also this sinking & sourcing concept is useful to answer PLC interview questions . Sinking and sourcing operations refer to electrical configurations of the circuit in the module & field input devices. When a device provides current when it is ON it is said to be sourcing current . When a device receives current when it is ON it is said to be sinking current. There are both sinking & sourcing field devices as well as sinking & sourcing input module. But it’s a common practice to use input module in sinking current mode. ·         Field devices on the positive side (+VDC) of the field power supply are sourcing field devices. ·         Field devices on the negative side (DC COM) of the field power supply are sinking field   devices. ·  ...

Here we are going to discuss about the Problems in contactors & their solution. Problems: 1) Over heating of main contact path 2)Overheating of coil 3)Noisy Magnets 4)Failure to pick up & seal 5)Failure to drop out 6)Excessive pitting and welding of contacts ...

PID instruction in Allen Bradley PLC [Proportional/Integral/Derivative] Closed Loop Control For   Processor SLC 5/02SLC 5/03SLC 5/04SLC 5/05    MicroLogix 1200 and MicroLogix 1500 (A special PID file replaces the old integer file control block.) Description of PID in PLC   This output instruction is used to control physical properties such as temperature, pressure, liquid level, or flow rate of process loops. The PID instruction normally controls a closed loop using inputs from an analog input module and providing an output to an analog output module as a response to effectively hold a process variable at a desired set point. The PID equation controls the process by sending an output signal to the actuator. The greater the error between the setpoint and the process variable input, the greater the output signal, and vice versa. An additional value (feed forward or bias) can be added to the control output as an offset. The result of the PID calculation (control vari...