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Active and Passive Barriers
Difference between active and passive intrinsic safety barriers

Can anyone give the difference differences between active and passive barriers. Why and where they are used?

By Enric_Tgn on 22 June, 2008 - 4:14 pm
1 out of 1 members thought this post was helpful...

A safety barrier, could be active and passive at same time. Imagine, for example, a loop powered pressure transmiter, placed in hazardous area,and connected to the DCS through a safety barrier. Since the transmiter is loop powered (pasive), the safety barrier, in their transmiter or hazardous area terminals, must be "active", due it has to suply energy for the loop powered device.

Futhermore, if the DCS field card is configured in active mode, providing the enrgy for the loop, our barrier, in their "safe area" terminals, must be pasive (allowing current flow from-to DCS in same value that flows in the barrier-transmiter system).
In general, an active device, provides the necessary energy for the loop, an a pasive device, is only a "receiver", and the energy comes from other device (active device) in the loop (i.e. a transmitter with auxiliar power terminals, configured in active mode).

It depends on the context in which the words active and passive have been used. For the intrinsic safety method of protection for instrumentation in hazardous areas.

In addition to the definitions given in the first answer I have seen the term "passive" used to describe shunt diode safety barriers. And the term active used to describe isolating type barriers.

Generally passive types are simpler and cheaper but require you to be more careful about the system/installation design. Active types are more expensive but are more tolerant of some things that can cause problems using shunt diode types.

Look for the "MTL Instruments" web site under "IS interfaces". They should give you a good introduction.

If you are doing a real design read well, take care and ideally get somebody experienced to help or check your design.

Hope this helps.


I presume you are talking about the difference between (passive) zener and galvanically isolated (active) barriers.

I am sure this has been discussed many times on here, is a link to one discussion I contributed to. Try using the search function on this site.

But basically zener barriers just provide the energy limiting that is required, active isolators offer additional functionality, zener barriers require no power but do need a low impedance safety earth, almost all isolators need power but don't require the earth.

Send me an email and I can send you one of our technical articles on the subject.


By Josh Albert on 5 June, 2014 - 4:33 pm

> Can anyone give the difference differences between active and passive
> barriers. Why and where they are used?

The barriers I am asking about have nothing to do with electronics. The application that I am investigating is the control of people in a warehouse environment. We are attempting to "control" the way they travel thru a certain area. We want them to enter and exit through a doorway and not to use the larger material transfer opening. Now that you have an idea on what we are trying to do, can you help?

By colin atkinson on 21 November, 2016 - 4:25 am

Passive barrier is more permanent, needs little or no management or introduction, e.g. a bollard or post that physically prevents a car passing, forcing the car driving to stop or find another Alternative route.

An active barrier in the same context would be a sign, light or road marking that indicated that a person should behave in a compliant way in order not to follow the undesirable route.

>Can anyone give the difference differences between active
>and passive barriers. Why and where they are used?

I got here researching for my PSP certification wondering probably the same thing you are probably wondering. I was looking into why there is a difference in CAD symbols for passive and active barriers like bollards and gates etc. To me, it would seem as if it sort of is an electrical or "alarm" issue?

Like an active bollard or gate has an alarm or sensor hooked up to it, some sort of electronic device. And a passive one does not.

More than just an access control issue. Is this more of what you were asking or am I way off?

The details of the topic is of course very complex. But the concept is very simple actually. The 'passive' and 'active' terms refers to the circuitry itself. To put things simple, Passive device requires no power VS Active device requires power to operate. Simple example: The computer audio speaker that requires power supply is called 'active speaker', and the one that does not need power supply is called 'Passive speaker'.

Passive device have only passive components within it circuitry to operate (ie resistor, capacitor, inductor, diode, etc.)..That's why it does not need power to operate.

Active device have at least one active component within it circuitry to operate(ie transformer, operational amplifier, LED), thus it need power supply to operate.

In intrinsically safe circuit for hazardous area, the benefit of active barrier lies in the galvanic separations(it behave like transformer - inducing power to isolated secondary side). it isolates hazardous area and safe area(so that fault within safe area is not being transferred to hazardous area). But in order to operate, the primary side of the galvanic isolation transformer must be powered up-that why it is 'active' type.

For passive barrier, the circuit only consist of resistor, zener diode, and fuse. It only trims the incoming input power, without isolating the incoming power - both hazardous area and safe area share the same 'common @ ground' connection.

That's why in hazardous area/field, equipment's ground connection MUST NOT being grounded to the enclosure. If they are connected then it will be considered as "Not isolated". I think I should add: you must ensure that equipment and enclosure have GOOD ISOLATION.

Nik Ammar
Petronas Gas Berhad