Level Measurement & Control


SIL2 for UWT’s rotating paddle ­series

October 2018 Level Measurement & Control

The terms ‘functional safety’ and ‘safety integrity level’ (SIL) have occurred more frequently since the publication of the international standard IEC 61508/IEC61511. Particularly in systems with hazard-causing processes, such as in chemical plants, the consideration of functional safety has become indispensable. On this basis, safety-related practices, design principles and error considerations must be met in order to minimise the risk of dangerous failures.

Rotary paddle level switch for overfill and dry run protection

The UWT engineers focused on this topic and redesigned the rotating paddle switch of the Rotonivo RN 6000 series according to the normative requirements of functional safety, to ensure safety functions in risk mitigation in accordance with SIL2. Typical functions include overfill and dry-run protection.

Depending on the requirements, the paddle switch is used as a full, demand or empty detector in storage silos or process vessels, and is suitable for use in almost all solids. With its simple electromechanical measuring principle it can also be adapted for extreme process conditions. A motor driven shaft causes the vane to rotate. Once the material level reaches the vane, thereby inhibiting further rotation, this creates a torque, which is converted to an electric signal. Once the vane is again free of the material, the output signal is reset and the motor driven shaft rotates freely once more.

As part of the functional safety issue, the electronics of the rotating paddle series have been redesigned. It has been reconfigured so that any failure of electrical components leads to a safe switching state of the output signal and thus a hazard by the system is avoided.

The innovative SIL2 compliant Rotonivo RN 6000 series now gives operators of safety-related systems a sensor in accordance with their specified safety integrity level along with an efficient level measurement transmitter.


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