Any recommendations for a barrier that I can use for just the sensor? The transmitter is sending a 0-5V signal back to my sub panel, but the route from the transmitter to the sub panel (including the transmitter) is in the safe area. The humidity sensor probe is is in the hazardous area and need the ISB. The current ISB has the transmitter and sensor downstream of the ISB.
Intrinsic Barriers
- Thread starter fifty60
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I am not finding any information on this topic. Is the setup I have so odd that it is not surprising that I am having difficulty? Transmitter out of the hazardous area with the probe inside the hazardous area. Is it more common to have an actual intrinsically safe transmitter/probe than to add an ISB to a non intrinsically safe transmitter probe? Is it assumed that only the probe will be downswtream of the ISB? The probe cable connects directly to the transmitter. I am not sure how I can put an ISB between the probe and the transmitter.
I am finding more information now. Is the concern that the transmitter is not rated as explosion proof? Should I be worried that the transmitter itself has a fault and has a spark or ignition at the transmitter itself? The transmitter is not located in the hazardous area, so this should not be a concern right?
Is the concern that the transmitter can store energy and release it as high power through the sensor probe? If so, how is that possible? Can someone explain how a fault at the transmitter that is downstream of an ISB can deliver unsafe power to the probe?
Is the concern that the transmitter can store energy and release it as high power through the sensor probe? If so, how is that possible? Can someone explain how a fault at the transmitter that is downstream of an ISB can deliver unsafe power to the probe?
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- Location
- Placerville, CA, USA
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- Retired PV System Designer
The IS system deals with stored energy as well as instantaneous power.
The barrier will limit what the transmitter can put into the sensor leads if a fault occurs in the sensor or the wiring to it. As long as the transmitter cannot store energy.
If the transmitter can store energy, it can take in power slowly through the barrier and release it all at once into the sensor if there is a fault. That is why equipment which can store energy has to be IS in design or else have a barrier on its sensor input, if the sensor is in a hazardous area or on the transmitter output if that runs through a hazardous area.
Just a barrier on the power input to the transmitter is not good enough.
Think of a 200 pound weight, which is raised to 20 feet in the air over the course of two hours by a very low power, geared down DC motor. Let's assume that there is not enough power in the DC supply circuit to hurt anyone. But what happens if you are standing under the weight when the hoist cable breaks?
petersonra
Senior Member
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- Northern illinois
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- engineer
that is part of why you need a control drawing. the control drawing will tell you what IS barrier will work with a specific device or devices and how it has to be wired. if there is no control drawing for a specific device than it is likely there is no suitable IS barrier.
your best source of advice on whether there is a suitable IS solution will come from the manufacturer of the device. just call them and ask. they can tell you and if there is a solution they can likely email you the details on how to implement it (AKA - the control drawing).
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