Intrinsically Safe equipment but still creating sparks?!

[phamgiatoanbk]

Hi all,

Here on a drilling rig we use some pressure sensor which is 4-20mA and Intrinsically Safe (IS). Everything is grounded properly... However, one day we observed that some sparks were generated when the sensor cable touch a metal part of another equipment. We are wondering from where could this spark generated?
Any ideas would be appreciated.

Thank,

Toan,

 

[BigInch]

I think they are only intrinsically safe .. when installed properly.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[micalbrch]

BigInch is as always on the right way. Electrical equipment is intrinsically safe if the power supply to the instrument is low enough so that an ignition cannot occur. So, it is not the sensor itself which is explosion proof but the installation. What voltage powers the sensor? A NAMUR amplifier can be installed between power supply and sensor to reduce the voltage down to max. 8 V which is usualy low enough to create any dangerous energy.

 

[ivymike]

Your pressure sensor has 4-20mA output when connected properly, but what limits the input current when the wires are shorted? As noted above it must be installed properly to be intrinsically safe. Current-limiting resistors are a common method for achieving that, see IEC 60079-11 table A1 for voltage vs. allowable short circuit current limit. You can calculate the required resistance for your power supply wire based on that info.

Excerpt from Rosemount 3051 manual, as an example of "requires proper installation":
Intrinsic safety Ex ia protection type
• Pressure transmitter with ia type protection shall operate with
a certified intrinsic safety power supply only.
• Closing of entries in the device must be carried out using the
appropriate Exe or Exn metal cable gland and metal blanking
plug or any appropriate ATEX approved cable gland and
blanking plug with IP66 rating certified by an EU approved
certification body.
• Pressure transmitter with intrinsic safety type protection is not
valid if it is not connected to an intrinsic safety circuit.