IS Device Question
IS Device Question
(OP)
I have an application for an oil flow meter in a Class I, Div II, Grp D envirnoment. We have always used a REN Slow Flow meter for this lube oil measuring task. However, this meter has no electrical approvals at all. I am told by the manufacturer that it can be used in hazardous locations with the use of a zener barrier.
How can I prove to an inspector that this is an aceeptable practice? Is this an acceptable practice? The flow meter is a purely resistive switching device. It cycles between 1 kOhm and 1000 MOhm as it switches. Used with a 24VDC input, this device generates a pulse train that we use to measure the oil usage. If this is acceptable, what code can I point to?

Thanks,
Chris Foley
Midland, TX
How can I prove to an inspector that this is an aceeptable practice? Is this an acceptable practice? The flow meter is a purely resistive switching device. It cycles between 1 kOhm and 1000 MOhm as it switches. Used with a 24VDC input, this device generates a pulse train that we use to measure the oil usage. If this is acceptable, what code can I point to?

Thanks,
Chris Foley
Midland, TX





RE: IS Device Question
I am surprised you need further proof. Sorry I do not know what code to point at but DO go to the web sites of barrier makers as they work pretty hard to explain their products and the necessity and may point out the code aspects.
Pepperl-Fuchs is probably the biggest supplier of barriers. Unfortunately their web site truly stinks. I do believe they have a great catalog loaded with info you could get from them. A sales guy could probably spout "codes".
http:
Gems is a good company too smaller but a better web site.
h
There are several other makers too. Google "zener barriers".
RE: IS Device Question
http://www.mtl-group.com/index.htm
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RE: IS Device Question
RE: IS Device Question
Thanks for the info. This pointed me in the right direction. Both datasheets for both of these mfgs referred to switches as simple devices. This lead me to search my new NEC CD for simple switches. It landed me in Section 504.2 Definitions.
The device that I am using is a totally passive device as it has been explained to me. I can now use a barrier for this device to create an instrinsically safe circuit as long as the inductance and capacitance of the wiring and the device do not exceed the limits of the selected barrier. I am aksing the flow meter mfg for an electical print to make sure that there are no signal filters or other capacitive or inductive components.
Thanks for your help.
Chris
RE: IS Device Question
Also the actual environment Hydrogen (worst), Acetylene:Ethylene Oxide (next), etc., all effect the allowed values. As in the above example 10uF @ 5V for Hydrogen, 10uF @ 7V for Acetylene.
I tell you this for the education and so if your instrument isn't simple realize there are options.
RE: IS Device Question
Thanks,
Chris
RE: IS Device Question
I will have to ask someone back at the company for the name of that book.
Maybe someone else will have another recommendation. I will try to get you the info. (may take a few days).
BTW if you have ever eaten a candy bar with nuts in it those nuts were sterilized in an ETO chamber controlled by a controller I designed. :) mmmmm nuts...