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Optical safe alarm for critical environmental conditions

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Contactless, currentless, safe

Companies and facility operators are faced with major challenges when it comes to process safety. Legal requirements, conditions and authorisations, internal specifications and potential risks to employees and the environment increasingly force the operators’ hand. Pressure vessels and pressure systems especially have to be protected against unauthorised loads. In this respect, bursting discs are considered a reliable and maintenance-free protective concept for all operating sectors. As well as these protective systems, the safe alarm is gaining increasingly in significance in process technology. Most new installations are equipped with additional sensors to transmit an emergency stop signal to the safety system of the entire facility if required. This avoids any extremely high consequential damage and long shut down times. Such damage can easily add up to six or seven figures.

For over 40 years, REMBE® GMBH SAFETY + CONTROL has been very successfully helping to avoid these enormous claims and minimise their subsequent costs using mechanical pressure release systems and the relevant burst sensor, among other things. In many cases, bursting discs are used with integrated or retrofitted detection systems which have a classic electrical interruption contact. If an emergency occurs within the facility, the bursting disc is triggered and snaps the sensor cable. The current flow is interrupted by the destruction of the wire and signals the event to the process control system. This type of monitoring is reliable and has been established for decades. In doing so, the actual signal transmitter (cable) is destroyed. The cable must be replaced after each response, like the bursting disc itself. This causes additional but avoidable costs.

The installation of such a classic burst sensor takes place in direct contact with the bursting disc. In critical processes with a low response pressure, the additionally applied bursting resistance (burst sensor) can negatively affect the system’s properties and significantly reduce the process safety. In comparison to this, there is a whole series of contactless procedures, such as magnetic, inductive and capacitive proximity sensors which have no influence on the bursting behaviour. This advantage is obtained with a higher sensitivity towards electrical and magnetic disruption signals, natural convulsions or vibrations. This can lead to false alarms, thus restricting their use in many areas.

Designed for critical environments

For systems with the maximum leakage requirements and smallest nominal widths, the market doesn’t actually offer any solution which causes uncertainty in the production process. To close this gap, REMBE® FIBRE FORCE GMBH in cooperation with its affiliated company REMBE® GMBH SAFETY + CONTROL has developed a new optical safe alarm, the SLR90. This contactless and currentless design is ideal for difficult and critical environmental conditions, to satisfy the requirements in chemical engineering, atomic structure, special constructions and facility construction.

A narrowband, specially modulated, optical signal is sent to the bursting disc to recognise the smallest changes caused by corrosion, leakage or bursting. This determined status information is transmitted in an isolated state to an easy-to-operate optoelectronic converter unit, converted into a conventional industrial useful signal, such as 1-5V, 4-20mA or for different bus systems (including PROFIBUS, EtherNet/IP, EtherCat, DeviceNet) and forwarded to the security system in real-time. As well as the continual status information, the optical SLR90 safe alarm function supplies a command signal as an alarm contact in the response case of the bursting disc, with which the system’s emergency stop can be triggered. The electroless signal is insensitive to electromagnetic parasitic couplings and is predestined for severe corrosive and explosive zones.

Easy adjustable

During on-site installation, no specialist knowledge or any prior knowledge about the optical unit is required. The burst sensor can be installed and set by any experienced fitter. The optoelectronic converter unit can easily be integrated into any switch cabinet using DIN top hat rail mounting and can be incorporated directly in the process control system as a Plug & Play component. The SLR90 is integrated on the side facing away from the process and is able to signal the lowest response pressures with process safety. Similarly, working temperatures on the signal transmitter of up to 350°C are possible in a special design. As a result, high-temperature processes can also be monitored, for which the market currently has no or virtually no solution.

The simple modular design of the SLR90 makes it possible to react quickly and individually to customer-specific requirements and to adjust the burst sensor to extreme conditions. For example, the SLR90 can be integrated retrospectively into the piping system in the field of ultra-pure media technology, downstream of the bursting disc screw-in unit. The space required for the burst sensor is less than 40mm when an additional screw-in unit is used. In almost all installation situations, retrofitting in the bursting disc holder or screw-in unit is possible.

In contrast to a classic interruption contact, the SLR90 does not need to be replaced when it has burst. This fact enables a long life span, reduces additional maintenance and shut down times and, with it, costs. In addition, the SLR90 can be connected as a separate and autarkic burst sensor into an existing system to achieve a higher safety integrity level (SIL), such as the required international standard IEC61508 / IEC61511. The focus is to monitor all components of a system with process safety.

In particular, bursting discs of small nominal widths (¼“ to 1”) with a minimal leakage rate, including the reverse bursting discs, could not be incorporated into the process control technology due to the lack of a solution. The SLR90 enables a signaling of such bursting discs for the first time. The safety of systems increases, while simultaneously reducing the potential risk to employees.

Author

Dipl.-Ing. Thomas Münstermann
Head of Process Safety Department / Product Manager
REMBE® GMBH SAFETY + CONTROL

T: +49 (0) 29 61 / 74 05 – 0
F: +49 (0) 29 61 / 50 714
sales@rembe.de
www.rembe.de

REMBE LTD

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