Robinson Bros keep lid on carbon disulphide with ABB transmitter 08 August 2013

Robinson Brothers is reporting success with a revised safety-critical level sensor, based on a magnetostrictive transmitter, which is now monitoring carbon disulphide (CS2) storage at its Midlands speciality chemicals plant.

Plant E&I manager Tom Rutter explains that CS2 is highly-reactive so is stored under a blanket of water. The interface level is therefore safety-critical and has to be constantly monitored.

Previously, he says, level measurement was via a magnetic float device, which provided local indication but without links to plant control systems. That needed to be changed under the site's improvement programme.

"Although other techniques were considered, a return to the tried and trusted method of a float, updated with the addition of a magnetostrictive level transmitter, was preferred," states Rutter.

Robinson Brothers called in instrumentation specialist ICA Services, which is an ABB WirelessHart (digital plant communications) distributor, which recommend ABB's AT100 magnetostrictive level transmitter.

The device is certified to ATEX Exd IIC T6 and can also be used in safety instrumented systems to the toughest SIL1 standard – essential for CS2-related instrumentation.

"The system provides process signals that output to both our local and site monitoring systems, and it meets our own internal requirement of SIL1-capable instrumentation," confirms Rutter.

And he adds that Robinson Brothers is now buying four more AT100 transmitters for use on its other CS2 process systems.

Magnetostrictive systems rely on a sensing tube and wire (waveguide) that is subjected to regular electrical pulses. These interact with the magnetic field created by a round magnetic float to produce torsional stress pulses, which are received by a piezo-magnetic sensing element in the transmitter that, in turn, calculates the float position.

Brian Tinham

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