Integrated isolation and power bridges the gap between USB and traditional industrial interfaces

September 21, 2015 //By Conal Watterson
Integrated isolation and power bridges the gap between USB and traditional industrial interfaces
Conal Watterson of Analog Devices looks at how integrated isolation and power bridges the gap between USB and traditional industrial interfaces.

As a standard for serial communication to peripheral devices, USB is ubiquitous today.

However, industrial devices still rely in many cases on the older standard of RS-232 for debug or master-slave connections. In order to add robustness through differential communication, RS-422 or RS-485 are also widely used, and RS-485 remains the physical layer standard used by various wired multi-node industrial network or Fieldbus protocols. As a result, there can be a mismatch between the available interfaces on tools used for debugging or monitoring, such as laptop computers that only have USB for serial communications, and industrial equipment, which may only expose RS-232, RS-422 or RS-485 interfaces.
 
In addition to the hardware interfaces required for any USB to UART translation, galvanic isolation is a functional and potentially safety requirement for any interface circuit between test or monitoring equipment, and industrial equipment that is potentially in active use, in an electrically harsh environment. Combinations of interface, iCoupler and isoPower isolation technology from Analog Devices, integrated together in a variety of ICs, allow easy solutions for bridging the gap between USB and
traditional industrial interfaces.
 
Why use galvanic isolation?  

When interfacing with industrial equipment, it is of paramount importance to avoid interfering with the operation of those systems. Galvanic isolation prevents any flow of current while allowing data transfer, protecting both the unit under test and the debug unit. When connecting debug consoles (for example, laptop computers), several hazards are apparent, as shown in Figure 1.

  • If the debug equipment is grounded, differences in ground potentials can result in loop currents
  • If the debug equipment is not grounded, static can discharge into the units under test
  • Hazardous voltages can occur on Fieldbus networks due to switching noise from motors and relays
  • Some basic diagnostic equipment (e.g. a laptop) may not have the same rigorous levels of interface protection as industrial equipment

 
Figure 1: Potential electrical hazards

In a USB

Design category: 

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