Zener Barriers with blown fuses, blinking error lights, and IS barriers in a Class I, Div. 2 area...
Are you ready to learn more about intrinsic safety? This is our second installment of Ask an Expert, where we sit down with a product expert and answer questions from customers like you.
Today's product expert is Robert Schosker. Robert is the product manager for Intrinsic Safety and WirelessHART products. Robert, thank you for joining us and let's get started...
Andy: The first question is regarding zener barriers, and the customer asks: "What are some of the common reasons for a blown-out fuse in a zener barrier, and how can I troubleshoot this?"
Robert: Thanks Andy, that's a great question! There are really only two common reasons why a zener barrier would have a blown fuse. One is either an overvoltage off the safe area side, usually caused by a failure in a power supply, or a short circuit on the hazardous area side of the zener barrier. And that's typically caused with the wiring that's running out to the field device. Both of those cause an excess of current to go through the fuse inside a zener barrier, and then the fuse blows. Now, the easiest way to check that - to see if your fuse is still active or still good - is to basically take an Ohm meter and check across the input terminals of the zener barrier. If you see a resistance there, you now know that the circuit is still good. If it shows up as an open, now you know that the fuse has been blown, and the barrier either needs to have the zener fuse replaced, or throw the barrier away and get a new one.
Andy: Alright Robert, the next question asks: "I have a power feed module KFD2-EB2, and it has a blinking red 'ERR' light. Could you please tell me what this means?"
Robert: The most common reason why a KFD2-EB2, our power feed module, would have a blinking red light, is if there is an error coming from one of the modules it is powering down along the UPR, or Universal Power Rail. That red light indicates that one of the intrinsic safety barriers has either a lead breakage or a short circuit indication to that module. It's a way for us to give you a visual indication that in that group of IS barriers, there may be a problem there. The other option could be that the module itself is having a malfunction. Either way, whether it is one of the isolated barriers or the module itself is having an error, the module gives you that red light to indicate that there is something wrong, and also a relay contact so that you can have a notification back at the DCS that something is wrong.
Andy: Alright Robert, this is the last question for this segment, and the customer asks: "I am looking for a barrier that will be able to connect to a device located in a Class I, Div. 2 area. Is this possible?"
Robert: Another great question Andy! In reality, you could put a barrier in front of a Class I, Div. 2 device, if you wanted to, but it really doesn't solve your problem. If you are going into a hazardous area, like a Class I, Div. 2, you don't necessarily need to use a barrier or intrinsic safety to get that device out there. You can just use a device that is rated for that area, assuming that the device is rated for the Class I, Div. 2 area, and then just use Div. 2 or non-incendive wiring techniques that are allowed by the NEC (National Electric Code). That's usually the easiest way to do it.
Andy: Well, that concludes this segment of Ask an Expert. I'd like to thank Robert Schosker for joining us today, and I would like to thank you for listening. If you have a question please feel free to contact us.