Ashu@automation

  Basics Of Automation and Fundamentals   Question :  In one of our control panel we had used some DO card  for exciting several 24V-relay .This system was being working without any problems maybe for years .But recently we find out some relays are not excited however the command of PLC exists. We checked the voltage on the solenoid of relay and measure it about 15 V as it should be 24 V Our question is that whether these cards have been damaged Answer: The voltage of 15V is too low. The voltage should be in a range of 23V. Please disconnect the load from the output, connect a resistor of appr. 480Ohm to this output. If the 15V stay furthermore, the module is defect or the load (L+/M-connection for the output group) is too low. Please check the power supply for the load. If this is ok, change the module.   Question : Any wrong access (datas, timer et.) will cause an interupt and OB121 will executed. Unlikely the error register...

Difference Between Warm Restart, Cold Restart and Hot Restart in Siemens PLC Warm Restart : In warm restart all non-retentive address like input output memory addresses are reset and cyclic program execution start at beginning. Cold Restart: It is same as Warm restart except that all even retentive memory are reset and cyclic programming start at begning. Hot Restart : No values are reset either it is retentive or non retentive. The program execution also start from where it is stoppped