Chinese
Spanish
Russian
Portuguese
French
German
Indonesian
Thai
Vietnamese
Arabic
Italian
Turkish
Polish
Japanese
Level alarm design begins with the consequence of continuing to fill or empty the vessel. The label high-high or low-low does not, by itself, define a safe setpoint, an independent trip or a restart rule. Specify what the process must do, how much time is available and which equipment carries out the action before selecting the METRAVON sensing device.
Level alarm design: give each threshold a distinct purpose
A high warning may allow an operator to arrange a delivery stop, while a high-high condition may demand an automatic action. If both occur too close together, the warning gives no useful response time. Define the operator task and the required automatic action separately, including what happens if the operator does not respond.
A low warning may request replenishment. A low-low condition may protect a pump or prevent a feeder from running without usable material. The relevant condition is not always the geometric empty level: a pump intake can uncover while liquid remains elsewhere, and a solid can stop flowing above the outlet while the upper vessel still contains stock.
| Duty | Define the action | Check before release |
|---|---|---|
| High | Operator response or routine control adjustment. | Is there enough time to act before the next limit is reached? |
| High-high | The specified automatic stop or other protective response. | What continues entering after the command, and which failures could prevent the action? |
| Low | Replenishment or a controlled change in operation. | Does the sensed location represent material still available to the process? |
| Low-low | The defined stop, inhibit or shutdown condition. | What must be restored and checked before equipment can restart? |
| Invalid | The response to a missing or unreliable measurement. | Can a failed sensor be distinguished from a genuine normal condition? |
Choose how the threshold is detected
A continuous measurement allows thresholds to be configured in a receiving controller. For a bulk-solids vessel, MV-RD21 radar is a candidate for following the material surface. The measured point must remain usable at the intended alarm height, including during filling and with the actual pile shape.
Several thresholds derived from one transmitter share that transmitter's failure modes. A second software alarm does not create a second measurement. If the project requires an independent high-high function, assess independence across sensing, supply, logic and the final action rather than counting alarm labels on the display.
The MV-SP601 RF admittance switch offers a point-detection route using a selected rod or cable assembly. Its sensing location is a physical installation decision. Confirm the active region, process compatibility and output configuration; probe length is not a continuous measuring span.
Allow for material that keeps moving after the alarm
For overfill assessment, determine the quantity that can still enter while detection, logic and final equipment respond. Include material already travelling through a chute or transfer line. Translate the required free space using the actual vessel geometry; equal height increments do not represent equal volumes in a cone.
For solids, the pile near the filling point may reach a roof opening before the surface under the radar reaches the same height. For liquids, agitation and surface movement may affect the usable measurement near the top. Include those conditions when locating the sensor and setting the operating limit.
Do not obtain extra nuisance-alarm filtering by consuming the entire response allowance. Specify delay and reset behaviour against the observed process variation and the time remaining for action. The accepted settings should be recorded and changes controlled.
Distinguish acknowledgement, reset and restart
Acknowledging an alarm tells the system that someone has seen it; it need not remove the underlying condition. A reset may clear a latched state only after specified conditions are satisfied. Restarting equipment is a further action that may require permissives or an operator command. Write those differences into the control description.
Consider a high-level switch that clears after a small amount of discharge. Immediate automatic restart may repeatedly refill the vessel to the trip point. The process design should decide the restart condition rather than inheriting an incidental relay transition.
Review the state after power restoration and after communications return. A previously latched trip, a stale high reading and an unknown sensor state should not all be treated as a normal cleared alarm. Establish the expected sequence for each case and test it with the controls team.
Prove the sensing and final action separately, then together
For MV-SP601, verify the transition with representative material present and absent, including normal residue. Coating rejection does not remove deposits or guarantee detection through every buildup condition. The installation and functional-testing guide covers probe placement and field checks.
For a radar-derived alarm, compare the reported level and quality with the receiving logic, then verify the threshold and invalid-signal response. A simulated input tests the logic downstream of that input; it cannot prove the radar's detection performance at a difficult high level.
Observe the specified final equipment action during an authorised test. Record response time, reset behaviour and any test limitation. Where a protective function requires formal safety assessment or certified components, that assessment must address the complete design. Neither product identification nor a successful operational test establishes a safety-integrity rating.
Questions about alarm specifications
Q1. Can the same transmitter provide process control and high-high protection?
It can provide multiple values or thresholds where supported, but sharing it introduces common failures. Whether that arrangement is acceptable depends on the consequence and the required independence. Obtain the responsible engineer's decision before calling the second threshold an independent protective layer.
Q2. Does de-energise-to-trip detect every wiring fault?
No. The selected circuit may respond to loss of supply or an open connection while remaining vulnerable to other faults, such as a short circuit. Specify the fault detection required and verify the actual input and wiring arrangement instead of relying on a general fail-safe label.
Q3. What makes an alarm quotation comparable?
Give each sensing point a duty, elevation and required action. Include the process and vessel conditions, output and receiving input, response allowance and test method. Ask offers to identify sensing hardware, logic and final-equipment responsibilities separately.
Summary
A workable alarm specification links a detectable condition to a timely, testable action. Send METRAVON the cause-and-effect requirements and vessel drawing to review continuous and point-level options without confusing an ordinary process alarm with an independently assessed safety function.
