Depending on the number of monitored channels required for a particular installation a flexible dip-switch located on the monitoring control unit’s PCB can be used to switch on and off specific monitoring channels. The power supply PCB also utilises a dip-switch which is used for the group relay function. In addition to the eight volt free contacts provided as standard for each monitored channel, the group relay function enables specifiers utilise two additional volt-free contacts so that these relays are energised only when all of the channels selected as part of the group displays a resistance of 10 ohms or less for each item of equipment. This means interlocked equipment will only be activated on condition that all grouped monitoring channels have equipment grounded to a resistance of 10 ohms or less.
Although there are effectively 10 relays located on the power supply PCB that can interface with the monitoring control unit’s PCB, communication between both PCBs is achieved via CAN bus. The CAN bus wiring, in conjunction with the IS power supplied to the monitoring control unit, means that four conductor cabling is all that is required between both units. This eliminates variations in cabling specifications and allows for a much more accurate prediction of cabling costs.
Earth-Rite MULTIPOINT II applications are not limited to examples like the drum mixing and filling process above. Process hazards ranging from railcar loading operations through to powder processing equipment can have their static ignition hazards reduced with the Earth-Rite MULTIPOINT II.
In this example the Earth-Rite MULTIPOINT II is configured to ground multiple interconnected components for a fluid bed dryer system. The marshalling box feeds seven channels out to seven permanent ground connection points. The connection points may be disconnected for routine cleaning, inspection and maintenance. Channels 1 to 7 are grouped together to provide a single output contact controlling the flow of powder into the fluid bed dryer. Channel 8 utilises an external ground status indicator station to provide the operator with a visual confirmation that the mobile bin is grounded prior to filling.
The Earth-Rite MULTIPOINT II’s monitoring control unit and remote indicator stations can be installed in Zone 20 atmospheres. The power supply unit can be installed in Zone 21 atmospheres. This configuration enables companies employ 24/7 monitoring of interconnected process equipment. This is particularly important when equipment is regularly disassembled and reassembled for cleaning and maintenance activities.
The Earth-Rite MULTIPOINT II’s software is written to the internationally recognised MISRA C protocol which has proven its reliability in the execution of safety functions across automotive, aerospace, medical, telecoms and industrial applications. Both the monitoring control unit and the powers supply unit have watchdog circuits that activate a fail-safe relay located on the power supply unit should the software of the embedded systems on either unit stop running. In addition to the watchdog circuits of both units, the monitoring control unit monitors the permissive threshold of each monitored channel so that if the permissive resistance range rises outside 0 to 10 ohms, e.g. a permissive condition is achieved with a resistance of 16 ohms, the fail-safe relay is activated. The purpose of the fail-safe relay is to ensure interlocked equipment does not continue to operate in the event that any of the equipment requiring active static grounding protection in the hazardous area may not be grounded.
Hazardous area certified.
The monitoring control unit and remote indicator stations are ATEX / IECEx certified for installation in Zone 0 / Zone 20 atmospheres and cCSAus approved for installation in Class I, Div. 1; Class II, Div. 1 and Class III atmospheres. The power supply unit is ATEX / IECEx certified for installation in Zone 2 / Zone 21 atmospheres and cCSAus approved for installation in Class I, Div. 2; Class II, Div. 1 and Class III atmospheres. The Earth-Rite MULTIPOINT II has been assessed in accordance with IEC 61010 Safety Requirements for Electrical Protection.
For a more visual representation of the Earth-Rite MULTIPOINT II and how the system can reduce static explosion risks in your operations, please visit our Application Videos section.
Mike O’Brien, Managing Director for Newson Gale
If you have any questions relating to the topics discussed in this article,
please contact Newson Gale.