Calculate the preset value (PT) for PLC timers (like Siemens S7) based on the desired time duration and the timer's time base.
In a Programmable Logic Controller (PLC), a timer doesn't directly understand "seconds" or "minutes". Instead, it works with a "Preset Time" (PT) value, which is an integer. This PT value is multiplied by the timer's internal "Time Base" (or resolution) to determine the actual time delay.
The logic is straightforward:
Where do I find the "Time Base" for my timer?
The time base is specific to the PLC model and the timer instruction you are using. You must consult the instruction set manual for your specific PLC (e.g., Siemens S7-1200, Allen-Bradley ControlLogix, etc.). For example, in Siemens TIA Portal, when you add a TON (On-Delay Timer), its time base is typically 1ms.
What happens if the result is not a whole number?
Since the PT value must be an integer, this calculator rounds the result to the nearest whole number. This means there might be a very small discrepancy (a few milliseconds) between your desired time and the actual time delay produced by the PLC. For most applications, this is negligible.