I have a 4-20mA non-loop powered E+H promass 83F40-AD2SAABAAFAS mass flowmeter. It is a 4 wire instrument. 2 wire to power the circuit boards with a 24VDC power source. Another 2 wire for the 4-20mA passive loop. The unit is ATEX II 2GD EEx d(ia) IIC approved.

Here is where I am losing it:
If it is EEx d - this means it is an ex-proof enclosure - so why do I need an IS barrier?

Why is there another rating of EEx d (ia) - which is IS protection class?

If I were to play it safe and put in an IS barrier for the 4-20mA passive loop. What about the 24VDC which is required to power up the rest of the circuit board. Do I need to have an IS power supply too? e.g. from MTL.

Or should I just power the entire unit using non-IS circuit i.e. do away with the IS barriers on the 4-20mA passive loop and power the rest of the circuit board using a normal 24VDC power supply.

 

The device uses mixed protection techniques because it presumably requires too much power to be made completely IS. The output signal is IS and can thus be mixed with other field signals in an IS multicore. Being IS, this will need connecting via a suitable IS interface mounted in the safe area.

Steve YATES
MTL
Hazardous Area Blog www.mtlblog.com

 

Eex d means that you have a flameproof enclosure, as you state.

(ia) means that it also contains "associated apparatus" for an IS system - probably the IS energy limiter (barrier or isolator). Since you have a 4-20 mA source in the flowmeter, this must have a barrier or isolator if it is to meet the requirements for IS. If this is the case, you wire the incoming power supply to the unit using Ex d rules, but the 4-20 mA output circuit to the passive load is wired using IS rules.

But you need to check the certification documents and installation instructions etc to make sure you meet any special requirements - see https://easy.endress.com/apps/pace/pdf_files/DMT00ATEXE074X.pdf for the certificate details. - in German.

HTH,
Bruce