Intrinsic circuit

[Eric911]

Dear all,
I read <<Intrinsic safety circuit design>> from Paul S.Babiarz. Somewhere make me confuse, may you give any advice?
Like you see in the documentation they apply 120V on low voltage circuit. I'm wondering what type of power supply they may have? how to transform 120Vac to DC voltage?

Thanks.

Eric

 

[dr pepper]

Never heard of that title, if its european then you might be talking about EN60204-1, if so I might be able to help on that one.

 

[KMoffett]

You really should post a link for online documents that you reference.

<<Intrinsic safety circuit design>> from Paul S. Babiarz

https://www.omega.com/pdf/temperature/Z/pdf/z131-148.pdf

I don't understand the rest of your question.

Ken

 

[dr pepper]

Nothing to do with en spec I mentioned so I'm out sorry.

 

[JimB]

Dear all,
I read <<Intrinsic safety circuit design>> from Paul S.Babiarz. Somewhere make me confuse, may you give any advice?
Like you see in the documentation they apply 120V on low voltage circuit.

The whole idea of intrinsic safety is to limit the energy which can flow from the safe area to the hazardous area (explosive gasses etc).
To acheive this energy limitation devices known as "IS Barriers" are used.
The power to a circuit which uses a barrier is usually 24v DC.
Anything higher that about 26volts (from memory) will "blow the barrier", isolating the hazardous area from the supply.

120volts is NEVER used in an IS circuit.

I'm wondering what type of power supply they may have? how to transform 120Vac to DC voltage?

Usually regulated 120 or 240 volts input power supplies with a 24volt output.
Something like these shown here. (Yes, there are lots of different types).

The power supply may be linear or switchmode.

JimB

On edit:

It is not the circuit that is intrinsic, there is no such thing as an "intrinsic circuit".

It is the safety which is intrinsic.
The idea is that the circuit from the safe area (for example a plant control room) out to the instruments in the hazardous area (a petro-chemical process plant), is intrinsically safe.
That is the instrument circuits cannot pass dangerous voltages and currents out to the field.

 

[Jaguarjoe]

Be careful, IS barriers are certified safe to provide some degree of assurance that they will perform properly. Homemade things are nice but if something went wrong with ISB made that way, it would be a legal nightmare.

I seem to recall zener diodes used for this stuff in the 3 paint shops I toiled in.

 

[Eric911]

Hi JimB and all,

Thank you for your wonderful explanation. Thank you all guy. Sorry, due to the time, the question is not very clear, but you give me a clear answer. Thank again.

Yes, you're correct in your comment. I'll use switch power supply for transform AC to DC, after switch power supply i'll use Zener diode for a Zener barrier. My confuse is what kind of standard will be follow for this switch power supply? I don't have any experience in IS circuit, only reference some document. So may you give any help or advice in this part?

Thanks for any help you can give me!

Eric

The whole idea of intrinsic safety is to limit the energy which can flow from the safe area to the hazardous area (explosive gasses etc).
To acheive this energy limitation devices known as "IS Barriers" are used.
The power to a circuit which uses a barrier is usually 24v DC.
Anything higher that about 26volts (from memory) will "blow the barrier", isolating the hazardous area from the supply.

120volts is NEVER used in an IS circuit.



Usually regulated 120 or 240 volts input power supplies with a 24volt output.
Something like these shown here. (Yes, there are lots of different types).

The power supply may be linear or switchmode.

JimB

On edit:

It is not the circuit that is intrinsic, there is no such thing as an "intrinsic circuit".

It is the safety which is intrinsic.
The idea is that the circuit from the safe area (for example a plant control room) out to the instruments in the hazardous area (a petro-chemical process plant), is intrinsically safe.
That is the instrument circuits cannot pass dangerous voltages and currents out to the field.

 

[Eric911]

Hi KMoffett,
Thank you for your link. I'm sorry the question is not very clear. Allow me describe it again.
I'll use switch power supply for transformer DC voltage, I'll use Zener diode barrier after switch power supply. My question is how to select this power supply? Any special requirement will be follow for this switch power?

Any help is welcome!

Regards,

Eric

 

[Eric911]

Hi Jaguarjoe,

Thank your for you remind, I'll try to avoid this problem.

Good day,

Eric.

Be careful, IS barriers are certified safe to provide some degree of assurance that they will perform properly. Homemade things are nice but if something went wrong with ISB made that way, it would be a legal nightmare.

I seem to recall zener diodes used for this stuff in the 3 paint shops I toiled in.

 

[Eric911]

Hi dr pepper,
Thank you for your comment. The circuit should be follow IEC60079 standard. It is used in dangerous places of standard.

Regard,

Eric

Never heard of that title, if its european then you might be talking about EN60204-1, if so I might be able to help on that one.

 

[ChrisP58]

There are so many subtle details in those safety standards that you really need to study them and make sure you thoroughly understand all of the sections that apply to your product. And one standard often refers to others that also need to be studied.

Expecting to be able to properly select and/or design an intrinsically safe product by asking a few questions in a general electronics forum is destined for failure. You don't even know all of the questions to ask. While you can ask for help here, the final decision needs to be yours.

The requirements for products that need to go into areas where a failure can cause extensive loss of life and property are not to be treated casually. If you don't do them right, you might end up killing someone. There are no shortcuts to safety.