Pepperl+Fuchs Blog

How to Connect a NAMUR Sensor to a Switch Amplifier

Posted by Robert Schosker on Thu, Feb 26, 2015

NAMUR sensors are used in hazardous locations, and can provide both explosion hazard and personal safety protection. NAMUR sensors and switch isolators are highly reliable and have proven-in-use characteristics, making them a perfect choice for safety-related applications when connected to suitable control circuits.


Most devices are independently rated with Probability of Failure on Demand (PFD) and Safe Failure Fractions (SFF) that enable them to be used in functional safety areas up to SIL2 or SIL3. In this blog, Product Manager Robert Schosker talks about how to connect a NAMUR sensor to switch amplifier KFA5-SR2-Ex2.W, and then tests to ensure proper operation.

Hi, I'm Robert Schosker, Product Manager here at Pepperl+Fuchs Process Automation Division. I'm in charge of intrinsic safety barriers. Today, I'm going to show you how to hook up a simple apparatus, or NAMUR sensor, to one of our switch amplifiers, and test it for correct operation.

Today's product that we're going to test is the KFA5-SR2-Ex2.W. As you can see in this setup, I have one switch amplifier lying on its side, because on each barrier that Pepperl+Fuchs makes, we have a wiring diagram. The switch amplifier that is shown on the DIN Rail is to demonstrate how we connect the wires to it.

For today's demonstration, we're going to need four accessories:

  • To get the barrier powered up, we need a simple power cord that allows 110 V to flow into it, because the barrier is powered by 110 VAC.
  • We're going to need a NAMUR sensor. This one happens to be a proximity sensor, so it senses metal.
  • A screwdriver. You need this to loosen or tighten the terminals on the barrier.
  • A paperclip! We'll use this for our simple apparatus.

I've taken the liberty of wiring up the NAMUR sensor and the power. You'll notice the power coming in - it's 110 VAC, connected to terminals 14 and 15. And then the NAMUR sensor, which is also a 2-wire device. It's connected to channel 1, which is terminals 1 and 3.

If you look closely at the top of the barrier, you'll notice our label carrier, and I will open this up so that you can see into it a little more clearly.

Now, I've removed the NAMUR sensor, and if you'll look at this close up, you'll notice that both lights are now blinking red for Channel 1 and Channel 2. That's because there is no sensor connected to the barrier, and our lead breakage and lead short circuit are activated.

If you are doing a dry contact, and that's all that you are doing, a pushbutton, and for this test a paperclip, you will want to turn off the lead breakage and short circuit indicators. These are located at switch number 3. If you look closely, I'll change it over. It changes from position I to position II. As I do that, the red lights stop blinking. What I've done is internally turned off the lead breakage and short circuit monitoring.

Next, I will put a dry contact across terminals 1 and 3, and you are going to see and hear the yellow LED light illuminate and click for Channel 1. What that indicates is that the barrier is working correctly. I'll even come up and do Channel 2, and again, it's working correctly.

As you can see, we've tested this intrinsic safety barrier with a simple apparatus, our paperclip, and we've tested it with a NAMUR sensor, and it's indicated that the barrier is working. Some of the things that you may not have seen or heard in this demonstration was when the relay switched, you would hear the relay change (a click) so you know that it was changing state inside the barrier. You also had the visual indication of the yellow LED. Secondly, the switches on top: S1, S2, and S3. S3 controls the lead breakage and short circuit. We were able to turn that one off when we were using a dry contact, but you should leave it on when you are using a NAMUR sensor. Switches S1 and S2 - those are designed for Channels 1 and 2, so you can change the mode of operation of the relay contact that is the output side of the barrier.

Questions about Intrinsic Safety? Get the Engineer's Guide

Topics: Inductive Sensors, Troubleshooting, Intrinsic Safety Barriers

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