Basics of PLC timer- PLC timers are instructions that provide the same functions as on-delay and off-delay mechanical and electronic timing relays. A PLC timer provides a preset delay to the control actions. In general, there are three types of PLC timer delays, ON-delay timer, OFF-delay timer and retentive timer on. The terms represented in the timer block in the PLC are a Preset value which means the delay period of the timer, an Accumulated value which is the current delay of the timer. A timer begins the counting on time-based intervals and continues until the accumulated value equals the preset value. When the accumulated value equals the preset time the output will be energized. Then the timer sets the output. Basic PLC Ladder Programming Training Example- Automatic Door Open Close System PLC Ladder Program PLC Ladder Practice Problem: When someone enters the infrared sensing field, opening motor starts working to open the door automatically till the door touches the opening limit switch If the door touches the opening limit switch for 7 sec and nobody enters the sensing field, the closing motor starts working to close the door automatically till the closing limit switch touched together. Stop the closing action immediately if someone enters the sensing field during the door closing process. Number of PLC Inputs Required X0 - X0 = ON when someone enters the sensing field. X1 - Closing limit switch. X1 = ON when 2 switches touched together. X2 - Opening limit switch. X2 = ON when the door touched the switches. Number of PLC Outputs Required Y0 -Opening motor Y1 - Closing motor Number of PLC Timers Required T0 - 7 sec timer. Time base: 100ms Number of PLC internal memory flag Required M1013 - 1s clock PLC Ladder Programming Description: X0 = ON if someone enters the sensing field of the infrared sensor. Y0 will be ON and latched, and the door will be opened as long as the opening limit switches X2 = OFF. When the door touches the opening limit switches, X2 = ON. The timer T0 will start to count for 7 sec if no one enters the sensing field (X0 = OFF). After 7 sec., Y1 will be ON and latched and the door will be closed. During the closing process, X0 = ON if someone enters the sensing field. The NC contact X0 will be activated to turn Y1 off. Because X0 = ON, X2 = OFF and Y1 = OFF, Y0 will be ON and the door will be opened once again. Follow Us On : Google Reviews : https://goo.gl/LxpEsU Facebook : https://www.facebook.com/wscubetech.india Twitter : https://twitter.com/wscube Linkedin : https://www.linkedin.com/company/wscube-tech Google + : https://plus.google.com/+wscubetechjodhpur Youtube : https://www.youtube.com/c/wscubetechjodhpur Website : http://wscubetech.com
