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A rotary paddle level switch reports resistance to paddle rotation, not the total contents of a hopper. Material packed around the shaft or trapped in a wall pocket can keep the switch operated after the main hopper has emptied. Treat that disagreement as a local material or mechanical problem before changing the controller delay.
Inspect the paddle location after a normal discharge
Use the site's isolation procedure before inspecting or touching the assembly. Preserve photographs and observations of the as-found condition where safe. Establish whether the sensing area is genuinely clear, covered by a stable deposit, or still surrounded by material because the hopper has bridged.
Those conditions need different responses. A blocked outlet is a process problem; a damaged shaft is a mechanical defect; a clear paddle with an incorrect controller indication requires electrical investigation. Cleaning everything first can remove the evidence needed to distinguish them.
| Observation | Next check |
|---|---|
| Packed pocket | Whether the connection recess or wall geometry retains material around the paddle. |
| Bent shaft | Incoming material impact, installation damage and the approved extension arrangement. |
| Clear element | Mechanical operation and contact-to-controller correspondence using the permitted test. |
| Light powder | Whether the chosen paddle and sensitivity suit the lowest actual bulk density. |
Do not alter a rotary paddle level switch by trial and error
Paddle size, shaft length and sensitivity affect the operating behaviour. A larger improvised paddle can change torque and structural loading. Request an approved combination using the bulk material, installation direction and filling method. Specify access for replacement without relying on reaching into an operating hopper.
Would an RF probe remove the original failure mechanism?
The METRAVON MV-SP601 has no rotating paddle and can be considered for point detection using RF admittance. That removes the paddle mechanism from the proposed design, but not the hopper's accumulation pattern. Persistent material surrounding the new probe may still represent real local coverage.
Describe residue when fresh, wet and dried, and identify whether it connects the sensing region to the vessel wall. A replacement proposal should address the actual deposit rather than using coating rejection as a promise of maintenance-free operation.
Q1. Should an alarm delay be increased to ignore retained material?
A delay cannot distinguish a deposit from a genuinely full hopper. Review the cause and the permitted response time before changing logic; otherwise a real high level may be reported too late.
Q2. What should a replacement trial include?
Observe filling, covered operation, discharge and return to clear with normal residue present. Record any cleaning needed between cycles so the proposed maintenance requirement is visible.
Summary
Locate the material that keeps the switch operated. Send the hopper section and after-discharge photographs before assessing an MV-SP601 replacement arrangement.
