Overview
In Siemens SIMATIC Manager (Step 7), implementing a "Hold ON" or latching logic in Ladder Logic (LAD) is a fundamental technique for maintaining an output state after a momentary input trigger. This is commonly achieved using a combination of contacts and coils arranged in a specific configuration.
🔄 Basic Hold ON Logic in Ladder Logic
To create a simple latching circuit, you can use a normally open (NO) contact for the input trigger and a normally closed (NC) contact for the reset condition. The output coil is placed in parallel with the input contact, forming a self-holding loop.
Example:
-
I1
is the input trigger (e.g., a push button). -
Q1
is the output coil (e.g., a relay or motor). -
I2
is the reset input (e.g., another push button).
Operation:
-
When
I1
is activated,Q1
is energized, turning on the output. -
Once
Q1
is energized, the parallel branch[ Q1 ]
keeps the coil energized even ifI1
is deactivated. -
To turn off
Q1
,I2
must be activated, breaking the circuit and de-energizing the output.
This configuration ensures that the output remains on until the reset condition (I2
) is met.