DART is a dynamic power supply and control system for intrinsically safe
fieldbus installations that dramatically increases the power available
to field devices in explosion hazardous areas, while maintaining
intrinsically safe energy levels. The product development took about 5
million euros investment and 10 years to accomplish.
“The DART system supplies enough power to support nearly as many devices
as is typically supplied in non-hazardous areas, and can also power
field instruments that previously required more power than intrinsically
safe solutions could offer,” says David Hohenstein, Department Manager,
Pepperl+Fuchs. “What makes DART so unique is that it enables process
users to fully benefit from the advantages of fieldbus technology in
hazardous area applications such as ensuring system availability and
lowering total cost of ownership.”
Early intrinsic safety solutions included the entity concept and
FISCO.
These enabled users to connect multiple devices to a single power supply
on a fieldbus segment, but the low available power limited the number
of devices per segment and reachable cable distance, forcing users to
design complex bus topologies with many branches, and making fieldbus
more difficult to cost-justify. More recently, the High-Power Trunk
Concept (HPTC) provided users with safe installation in explosive
environments, with more power supplied to the fieldbus segment while
maintaining intrinsic safety at the device connection. According to the
company, DART represents a revolutionary next step in the evolution of
intrinsic safety.
“DART is an exciting and superior option because it eliminates the power
problem of intrinsic safety with a completely new approach to energy
limitation. It allows for considerable higher direct power, while
maintaining limitations on intrinsically safe energy via rapid
disconnection,” explains Hohenstein. “Rather than taking a traditional
approach to explosion prevention by limiting the available power to
field devices, the DART system detects a fault condition by its
characteristic rate of current change, and disconnects power before
sparking can start.”
During normal operation, a DART power supply feeds full nominal power of
8 to 50 watts – exponentially more power than the approximately two
watts that is normally permissible in intrinsic safety environments.
Should a fault occur the potential spark remains non-incendive, and DART
detects the resulting change in current and immediately switches off
the power supply. In microseconds energy from the electrical system is
reduced to a safe level, robbing a spark of the energy needed to ignite
hazardous gases.
DART applied to fieldbus provides a much higher intrinsically safe power
allowance to the trunk so that the segment can support up to about 32
devices per segment – the maximum permitted per segment. This reduces
capital costs by eliminating excessive fieldbus infrastructure.
Moreover, cable lengths as long as 1000 meters are possible, opening up
many application areas to fieldbus technology while maintaining
intrinsic safety requirements for all devices and cables, including the
trunk line. The higher device count per segment eliminates the problem
of having to design complex network topologies with many sub-segments,
each requiring its own power supply, junction boxes, and barriers.
DART technology also offers advanced diagnostics to help users rectify
problems quickly and ensure system availability. And because DART
Fieldbus is designed as a fieldbus infrastructure for existing IS field
devices and DCS systems, or for any installation in which an
intrinsically safe fieldbus segment is required, it is suitable for both
green- and brown field sites.
Source: Gary Mintchell's Feed Forward Blog
