Barrier or Galvanic Isolator

Z

Thread Starter

zare.v

Dear Sir,

I would like to know more detailed about Barrier and galvanic isolator application. I would greatly appreciate if someone can help me on following matters:

1- Is it possible to replace a barrier with a galvanic isolator in specified application? Or do we have to consider the property of the device, meaning to know whether it is intrinsically safe or explosion proof?

2- When a device is explossion proof (Exd) is it necessary to use a barrier or galvanic isolator? Or do we only use barrier (or galvanic isolator) for intrinsically safe devices?

Best regards,
Zare
 
B

Bryce Gillan

1 - Either Galvanic isolators or barriers can be used as a component in an intrinisically safe loop to limit the energy in the hazardous area. There are pros and cons for either type of protection. An intrinsically safe loop can be implemented fully with intrinisically safe apparatus or the galvanic isolators or barriers can feed associated electrical equipment that has an alternative method of protection (e.g. Exe or Exd). Some countries e.g. Germany insist on using Galvanic Isolators for circuits connected to zone 0.

2 - The barrier or galvanic isolator can be used with an explosion proof device as part of an intrinisically safe loop if you want to use lower cost cable without mechanical protection (e.g. no wire armour or conduit) from the safe area to the equipment in the field.

Regards
Bryce
 
N
Zare,
Both Galvanic and Zener Barriers are used for Instrinsically Safe circuits, the difference being that is no electrical connection between input and output in a Galvanic barrier but there is a connection in a Zener Barrier.

Explosion Proof is where an Instrument is housed in an Explosion Proof enclosure, that means that an explosion is allowed to occur within the enclosure, providing it does not affect it's surroundings. In other words, it must contain the explosion within the enclosure.

Intrinsically Safe is where the current in the circuit is limited so that it does not have sufficient energy to create a spark, if shorted. In other words it is not able to cause an explosion in the first place.

Hope that helps.
 
S
This is only true if the terminals to which the IS barrier is connected are certified as being IS (or the device is considered as Simple Apparatus) otherwise there is a risk that energy contained within the device could be released into the cable connecting the device back to the barrier and any spark generated at any connection could be incendive

Steve
 
Mr.Steve,
Thank you for your attention.
Would you please give more detailed about the matter you stated in your reply?
I do appreciate your advice.

Zare
 
Please accept my thanks for your conern.
I supposed that when a system is IS, we do not need to use any isolation between hazardous site and Non-hazardous area,Since the energy has been limited in IS device.

Thank you for your advice.
 
Thank you for your concern.
As you stated IS means that the current in the circuit is limited so that it does not have sufficient energy to create a spark, so in this case is it necessary to use an Isolator? Or it can be connected to receiver directly?
I supposed that for Non-IS systems, we have to use Barrier or Galvanic Isolator for isolation site and non hazardous area.

I do appreciate your advice.
 
B

Bruce Durdle

Hi Zare,
As you state, the energy is limited in an IS system. The barrier or isolator provides only a part of this limit - it ensures that current or voltage fed to the hazardous area from a source in the safe area are themselves insufficient to cause ignition of the atmosphere.

However, even if voltage or current are low, the energy that can by delivered to a break in the circuit also depends on the inductance or capacitance. So any device connected into the circuit downstream of the barrier or isolator musty also be certified as IS, and the total connected inductance or capacitance (including that of the connecting cables) must be less than the maximum permitted by the barrier or isolator certification.

To summarise - you MUST have an isolator or barrier supplying an IS circuit. All components connected into the circuit must also be IS - you cannot convert a non-IS system into an IS one simply by adding a barrier or isolator.

Cheers,
Bruce.
 
No, you're statement is wrong.

You must have either a passive barrier or an isolator between the hazardous and non-hazardous area to protect against faults in the safe area.

For instance when a technican working in the safe area drops his screwdriver that falls and shorts between AC line voltage and an open terminal going to an IS circuit.

The barrier or isolator protects the IS circuit in the hazardous area from receiving the fault current/voltage/power that is accidentally applied to the IS circuit in the safe area.

David
 
S
Intrinsic Safety is based on the restriction of the energy that is present within a loop, this not only means the energy transferred from the Safe Area but also the energy stored within the field device and the cable. If the field device is not certified as being IS, then any energy stored within it could be released back into the field wiring and thus increase the total energy in the loop. This could present a risk if there were any loose terminals as it could be released in the form of an incendive spark. These terminals could be on the field device or in junction boxes.

Steve
 
You do not need isolation between the Safe and Hazadous Areas for safety reasons but may you decide you want it for operational reasons so using IS galvanic isolators gives you both functions in a single device.

Steve
 
S
In most countries, devices that are not by themselves energy storing or energy generating do not require certification. The use of "Simple Apparatus" is one of the attractions of Intrinsic Safety over other protection techniques because it means you can use un-certified junction boxes, thermocouples, pressure switches, etc.

Steve
 
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