ADVANTAGES:

  • Input / Output galvanic separation, no need of an isopotential ground system
  • Allow use of not isolated field elements
  • Electrovalve driver always safe even during the fluctuations of the coil resistance due to ambient temperature variations
  • Protected against short circuits
  • Can be inserted or removed from the loop without shutting down the power

DISADVANTAGES:

  • Higher internal volt drops than passive barriers
  • Higher cost than passive barriers

Three types of loop powered isolated barriers are usually available: isolated current repeater for transmitters, isolated current repeater for electropneumatic converters, and electrovalve drivers.

The first two use the 4-20 mA signal as power supply, while all of them use the DC/AC conversion, an isolation transformer, and the AC/DC re-conversion to obtain the galvanic separation between the hazardous location circuit and the non-hazardous location one.

They are mainly used when an isopotential ground system is not considered or the field elements are not isolated from ground, without using powered barriers, and a power supply voltage (or an input signal), able to overcome the major internal volt drops typical of this types of barriers, is available.