Hi,
We have an application of sending a non-IS signal between two buildings, using exiting IS cabling through a hazardous area. I am thinking of using an IS barrier isolator at each end.
Typically, in an IS system, there is a barrier isolator inside the safe area. The non-IS side of the barrier is connected to the control or safety system, and the IS side is connected to a field instrument in the hazardous area.
In our case, the two ends are both in safe areas (two different pressurized buildings - Ex p) but the existing multipair wiring between the two is IS through a hazardous area. Using a single barrier isolator at one end (system termination side) is not sufficient, as the IS circuit needs to be connected to an IS certified device at the other end (or a simple device, like an RTD – but it is not our case). Since the other end is not an IS device, I thought of using a second isolator barrier where the two IS sides of the two barriers are connected to each other.
For a 4-20mA signal, one sinks the current and the other end sources. The IS calculations would be very easy using the other barrier parameters as the field device parameters for the other barrier. It is easier for a digital signal, as one side will have a DI barrier and the other one will have a DO barrier with a dry contact relay which is a simple device. All governed by IEC 60079.14.
Does the above make sense? Appreciate if you could share your thoughts.
Thank you!
We have an application of sending a non-IS signal between two buildings, using exiting IS cabling through a hazardous area. I am thinking of using an IS barrier isolator at each end.
Typically, in an IS system, there is a barrier isolator inside the safe area. The non-IS side of the barrier is connected to the control or safety system, and the IS side is connected to a field instrument in the hazardous area.
In our case, the two ends are both in safe areas (two different pressurized buildings - Ex p) but the existing multipair wiring between the two is IS through a hazardous area. Using a single barrier isolator at one end (system termination side) is not sufficient, as the IS circuit needs to be connected to an IS certified device at the other end (or a simple device, like an RTD – but it is not our case). Since the other end is not an IS device, I thought of using a second isolator barrier where the two IS sides of the two barriers are connected to each other.
For a 4-20mA signal, one sinks the current and the other end sources. The IS calculations would be very easy using the other barrier parameters as the field device parameters for the other barrier. It is easier for a digital signal, as one side will have a DI barrier and the other one will have a DO barrier with a dry contact relay which is a simple device. All governed by IEC 60079.14.
Does the above make sense? Appreciate if you could share your thoughts.
Thank you!
