Precise full detection despite heavy buildup

In the course of the modernization of several plants with regard to wastewater regulation, a water company was looking for well-functioning, long-lasting measuring technology for level determination. The privatized corporation has been operating in England since the 1970’s, providing fresh water and ensuring sanitation in central England. The most exciting processes involved wastewater handling, where a blockage indicator within a transfer hopper was required. The challenges were mainly that the material is in a high solids slurry condition, heavy build up and requires a Gas Zone 1 certification.

Several tests were carried out on site together with the team from UWT (UK) Ltd. Due to the challenging process conditions, a decision was made in favour of the classic and tried and tested solution of a rotating paddle switch. Depending on the requirements the rotary paddle level sensors are used as a full, demand or empty detector in storage silos or process vessels and is suitable for use in almost all solids. With their simple electromechanical measuring principle, they can also be adapted to extreme process conditions. The UWT rotary paddle level switches can be used in applications with process temperatures of up to 1100°C and process pressures of up to 10 bar. The robust and versatile functional principle is based on a motor-driven, rotating measuring blade, which is inhibited in its rotary motion when covered with bulk material. This creates a counter-torque which is converted into the electrical output signal “covered” via a swivel movement at a switch. If the bulk material no longer covers the measuring blade, the switch is reset to its initial position via a spring. The original state is reached again, the output signal is inverted.

Installed was the rotary paddle level limit switch Rotonivo^® RN 6001 mounted through the side wall of the hopper. The device could be optimally configured for the application and saved the operator time and money as a unknown blockage would cause major issues for the whole process. It has all current international approvals for use in gas and dust explosive atmospheres and is one of the first rotary vane detector certified according to SIL 2. The sensor also works reliable with very strong cacking at the probe and overfill protection is guaranteed for the long term.

Side trip into the world of functional safety

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 minimize the risk of a dangerous failure.

Rotary Paddle Level Switch for overfill and dry run protection

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

Depending on the requirements, the Rotonivo^® rotary 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 preventing further rotation, this creates a torque, which is converted via a switch to an electric signal. Once the vane is free again of the material, the output signal is reset and the motor driven shaft rotates again.

First rotating paddle limit switch with SIL2 worldwide

As part of the functional safety issue, the electronics of the rotating paddle series Rotonivo^® RN 6000 have been redesigned. This has been configured so that any failure of electrical components lead to a safe switching state of the output signal and thus a hazard by the system is avoided.

With the innovative SIL2 compliant Rotonivo^® RN 6000 series operators of safety-related systems have a sensor system in accordance with their specified safety integrity level and the perfect content level measurement component in their safety circuit.

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Solution partner for level measurement since 1977 with comprehensive expertise in all industries and process applications. UWT is a medium-sized German family owned business and has become one of the world’s leading experts in the field of level measurement technology offering innovative sensors for continuous and point level measurement in any …