Pepperl+Fuchs Blog

5 Questions Answered: Intrinsic Safety Barriers

Posted by Zach Lohr on Wed, Aug 22, 2012

Question one

K-System intrinsic safety barriersI have a KFD2-UT2-Ex.1 and would like to know what software/hardware I need to have?

A) The PACTware software and interface technology DTM software are free and can be downloaded from our website. One nice thing to point out is all Pepperl+Fuchs intrinsic safety barriers use the same DTM. You will also need a cable to configure a barrier. You can use either the K-ADP-1 (RS-232) or K-ADP-USB (USB).

Question two

I have level measurement devices that require 24 VDC, 4-20 mA, loop power, and HART capability. Which intrinsic safety barrier is best?
A) The IS barrier KCD2-STC-Ex1 is the right choice. This barrier offers source and sink mode via DIP switches. Other IS barriers would typically be used, but because your devices require HART capability, the KCD2-STC-Ex1 is the one you should use. The sink mode enables the DCS to think it’s powering the barrier and field device; hence the loop power is required. The barrier and field device are actually powered by the DIN Power Rail or a separate 24 VDC supply.

Question three

What is a load cell? And how would I use your intrinsic safety barriers to wire it up?

A) Load cells are the latest in weighing-based technology. We can do this with either a zener barrier, or with K-System.

Your first option is the Z-System. A Z966 zener barrier supplies a 350 ohm strain gauge bridge with the necessary excitation voltage. The Z964 zener barrier will supply the power supply with a voltage sense input for increased accuracy. The millivolt signal is transferred to the safe area through the Z961 zener barrier.

Your second option is the galvanically isolated KFD2-WAC2-Ex1.D. With its 3-way isolation between power supply, input, and output, this barrier provides a highly accurate means of supporting strain gauge applications within a hazardous location. The strain gauge can be connected in either a 4- or 6-wire configuration, depending on the required accuracy. The strain gauge excitation voltage, mV signal range, tare value, and current output range are all field selectable in the barrier.

Question four

I am using a fieldbus and had questions regarding termination. If my trunk line is 20 feet, and I have hundred foot spurs, do I still want the terminator at the Segment Protector?

A) Yes. As a general rule to ensure proper digital communications you will always have a terminator at the beginning and end of your network. Most of the fieldbus physical layer components on the market today have built-in termination. It a matter of flipping a dip switch or installing the terminating resistor at the power supply and on the end Segment Protector on the segment. In the case of the R2 Segment Protector, by design it prevents over termination, the only location the terminator can be placed is in the ONLY open trunk out terminal on the T connector. It also allows the disconnection of the Segment Protector while leaving the trunk communications uninterrupted.

Question five

Will the KCD2-STC-Ex1 and KFD2-STC4-Ex2 work with multi-drop HART loops? The datasheet shows only one transmitter connected on the hazardous side.

A) Yes. Our intrinsic safety barriers do work with multi-drop HART loops.


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Topics: Ask an Expert, Intrinsic Safety Barriers, Zener Barriers

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