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‘The Right Way to Safety’

17 January 2010

PR electronics has launched a set of six intrinsically safe interfaces to connect a control system to sensors located in a hazardous area. They cover every common application involving analogue, digital, or HART® signals. Called the 9000 system, it was developed ‘from the ground up’ according to the IEC 61508 standard.

PR electronics I.S. signal conditioning system
PR electronics I.S. signal conditioning system

Niels Praest of PR electronics says that while many of his competitors have intrinsically safe barriers, few if any of them were developed, as PR electronics has done, ‘from the ground up’ according to IEC 61508.

‘They have, for the most part, taken their existing I.S. products and adapted them to the standard,’ he says.

The new interfaces can be installed in a safe area or in a zone 2 area. And they come with a 5-year guarantee.

The interfaces are intrinsically safe isolation barriers. This means their circuits are energy-limited, so that any heat or sparks created by the sensors in the hazardous area are insufficient to ignite an explosive atmosphere.

Mr. Praest says isolation barriers have many advantages over zener barriers, such as lower installation costs, because grounding is not necessary. Creating and maintaining I.S. grounding can be expensive.

The modules also have the advantage of maintenance-free operation and prevention of ground loops and asymmetrical noise effects.

Mr. Praest says that his company’s SIL 2 certification guarantees that the hardware development, software development, test methods and test results are in conformity with IEC 61508, and that the built-in safety concepts make the I.S. interfaces safe to use as part of a SIL 2 application.

Niels Praest of PR electronics
Niels Praest of PR electronics

‘Worldwide, only a small number of electronics manufacturers have achieved a similar approval for their working methods.’

Power Rail design
Intrinsically safe control panels are usually characterised by massive amounts of wiring. To keep this to a minimum, the system designers build their concept around a ‘Power Rail’ that takes care of the power distribution and also accommodates alarm signals.

The interface modules snap onto the power rail — a tailor-made DIN rail — along with two supply units: A universal power supply with 24 VDC output and a power control unit, which distributes the power to the modules via the power rail.

The power control unit detects alarm signals from the modules on the power rail. Each module has a status relay for individual surveillance as well as a relay for collective surveillance via the power rail. An alarm is sent in case of error in supply, sensor, loop or hardware.

The user is informed of module status and any sensor errors by way of the status relays, the analogue, digital, or HART® output, and the front LED/display.

Furthermore, the 9106, 9113 and 9116 also feature automatic detection of active / passive analogue output via the same two terminals.

(All of the modules in the 9000 series can be mounted on a standard DIN rail and connected to a separate 24 VDC power supply.)

Front display
In trade show displays and in the photographs of the product in brochures, PR electronics shows the modules with front displays. But these are not permanent. After configuration, the displays can be removed and used on other units. Or they can be left in place to show current process variables.

The power supply and power controller are on the left side.
The power supply and power controller are on the left side.

The displays have scrolling help texts in 7 languages, which guide the user through the configuration steps. All selections are made by way of the front push buttons on the display. The user is completely independent of PCs, DIP-switches and jumpers. No laptop with configuration tools is needed.

When mounted in the process, the display shows process values and module status and indicates any sensor errors or input signals outside range.

The display also allows copying the configuration from one module to others of the same type (9113 and 9116). It can also be used to protect the configuration with a password.

Isolation, EMC
The I.S. interfaces provide signal conditioning with 2.6 kVAC galvanic isolation and have ‘far better EMC performance than required by the EMC directive’ (IEC 61326) and NAMUR NE21, as these interface also comply with IEC 61326-3-1 (EMC for functional safety).

In addition, the 9000 series complies with NAMUR NE43 (sensor error) as well as the Low Voltage Directive (LVD) and carries marine (DNV) and UL 61010-1 approvals.

Some of the first modules were shown in late 2009. The whole series is expected to be ready for the market during the first quarter of 2010. They will carry the following approvals: IEC Ex, ATEX, FM and GOST Ex.

For more information, visit www.prelectronics.com


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