Difference: Definition: On-delay timer: The on-delay timer is the most common and basic timer in various PLCs. This timer is called SD timer in SIEMENS PLC. Hold-type on-delay timer: This timer generates a latch function when the input condition 00000 is ON, even if the input condition 00000 becomes OFF, the input condition is still … Continue reading What is the difference between the on-delay timer and the keep-alive timer in Siemens PLC?