As we know for any intrinsically safe instrument we should install a safety barrier to limit the energy fed to the instrument.
My question is: what happens if we install an intrinsically safe instrument without installing a safety barrier before it?
Will it operate/run well?
What will be its Ex protection capability in that case?
The barrier is for Fire Safety.
You should know that it is based on the Area Classification for your section of plant.
The instrument will operate and run properly. However, it will no longer be an intrinsically safe installation, it will not meet Ex requirements because in the event of a power supply failure there will be the capability of producing a spark with sufficient energy to ignite an explosive gas.
The purpose of the I/S barrier is to prevent electrical faults (over voltage) in the safe area from getting to the I/S device in the hazardous, where the fault could damage the device and create an arcing-sparking ignition source.
No barrier; no protection from faults on the 'safe' side.
You will find that most modern 2 wire instruments are supplied rated as general purpose NEMA-4, IS and explosion proof.
If you install it without an IS barrier it is only certified for GP service.
Install it is a proper IS loop with correct wiring and an IS barrier and it is rated IS.
Install it with the proper Ex-d rated conduit, fittings and cabling and it is Ex-d.
It may technically work, but it not legal to operate in a classified area. You will not be able to calculate the EX(i) proof, because you would not have the required data.
It is not a good idea to use it in this way in an classified area.
If you have it in a non classified area, it may be your choice, but you need to mark it so nobody can do something wrong.