Continuous Dosing Refill Sequence: Valve, Horn and Feeder Interlocks

Refill is more than opening a valve. It is a short state machine that must replenish material without corrupting the weight signal or the normal flow-control loop.

Why one IF statement is not enough

If the refill valve opens immediately whenever weight is low, material impact and mechanical vibration can disturb the load-cell signal. If the kg/h controller keeps reacting to that disturbed signal, it may control the refill transient instead of true consumption.

Separate states to make the logic readable

States such as M20=Normal, M21=Refill and M22=Settle make it clear which outputs are allowed and which calculations are temporarily held. The horn can be tied to a specific refill event, while feeder behavior—continue, slow down or stop—should be an explicit process decision.

Minimum interlocks

• Force the valve closed at high-weight or upper-limit condition
• Block automatic refill if load-cell or analog validity is lost
• Alarm if valve feedback disagrees with the commanded state
• Hold or separately treat flow calculation during the post-refill settle window
• Stop and E-stop override every refill state

The return condition matters most

Many problems appear not when refill starts, but when the machine returns to normal control. Decide whether valve-closed is sufficient or whether weight-rate stability and a minimum settle timer must also be satisfied before kg/h control resumes.