Non-contact Temperature Sensor Safety?

[awillms]

Greetings,

I am not sure if I am in the right place to ask this question. I did a Google search and found a post here regarding infrared thermocouples, so I will give it a try.

I am working on a project where I need some non-contact temperature sensors for measuring a liquid surface temperature in an explosive environment. What I am after is a non-contact sensor with a Class 1, Div 1, Group D safety rating. Do any of you know of such an animal?

If I am in the wrong place and anyone has any suggestions as to where I might find the answer, please let me know.

Tony

 

[Steve Etter]

If I were in your shoes, I would try www.omega.com. They are big in the temperature measurement arena and should be able to help. I personally like to call and talk to a real person on applications where I am out of my element. I have found their applications people to be pretty darned helpful.

Steve

 

[awillms]

Thanks Steve.

I have been in conversation with Omega, but none of their sensors meet the Class 1, Div 1 Safety rating. I am trying to find an option that doesn't include having to place these sensors in an explosion proof container.

Any other thoughts or ideas?

 

[jimbo3123]

I had a similar situation about a year ago.
What we ended up using was the standard Raytek CI sensors with Stahl Intrinsically safe barriers.

I don't know if this is what you're looking for, but It was a cleaner and cheaper setup for us than using field devices that were Class 1 Div 1 rated.

 

[Steve Etter]

I agree that jimbo has probably got the best idea. My experience with Class 1, Div 1 makes me like the intrisically safe techniques much more than the explosion proof.

I did a search of my own on the web and also came up dry for acceptable infrared sensors.

Steve

 

[awillms]

Thanks everyone. That wasn't what I wanted to hear, but it is what I expected. At least it is good to have come confirmation of what I thought was the case.

Do any of you have any experience with Omega's IR Thermocouple design? If so, are they as good a deal as their literature makes it sound?

Tony

 

[dash]

Since you didn't specify which IR unit from Omega, what I am about to say needs to be verified.

I did not see a 4-20mA, two wire transmitter option. You will have to have a simple two wire device to install an intrinsically safe barrier. Also, those units look a little light duty. I would tend to stick with someone like Raytek, which at the moment is the only one I found that has two wire interface. I thought I had bought one from IRCON before, but I guess I was wrong.

Here is a link to the Thermalert TX series. Which I know I have bought a two wire version of.

http://www.raytek-northamerica.com/...=show&id=1013459159&tool_id=14&cat_id=2.2.2.1

If you go this route make sure you educate yourself on the proper installation of the intrinsically safe barriers you choose & read the appropriate section in the NEC for installation recomendations.

Darren

 

[jimbo3123]

You will have to have a simple two wire device to install an intrinsically safe barrier.

This is not true.
I used Raytek CI temperature sensors. These required a 12-24VDC supply. I did need to use an intrinsically safe power supply though. They had a pseudo-theromcouple signal line that went back to my PLC (through an intrinsically safe barrier)

 

[godfrey]

Try Land Instruments. landinst.com

 

[JesperMP]

Hey guys, are you sure that the proposed approach is acceptable ?

You seem to imply that you can make anything "Ex" proof by simply connecting it via intrinsic barriers. Dont you forget that this is only acceptable for simple devices that cannot store energy (like switches and such). Electronic devices must have the Ex "i" mark to be allowed to be put in the hazardous area, even if they are connected via bariers.

 

[dash]

The Raytek two wire unit (TX series) is available with an intrinsic safety rating. I have found that in the US it is much more common for two wire devices to have ratings to be used in an intrinsically safe system. For the US it must meet ratings from ANSI/UL 913-1997.

JesperMP's point is well taken, if not familiar you should read the NEC Article 504 on intrinsically safe systems.

Darren

 

[awillms]

The unit from Omega that I inquired about earlier is the OS36 model - what they are calling an Infrared Thermocouple. Here's the link: http://www.omega.com/ppt/pptsc.asp?ref=OS36&Nav=temj09

Omega claims this is intrinsically safe in portions of their literature, but makes no such claims elsewhere. I am not sure, however about the Class 1 Div 1 rating.

Thanks for all of your help and suggestions!

awillms

 

[dash]

If it is truly self powered (whatever that means) you would still need to purchase a thermocouple intrinsically safe barrier. It looks like that it behaves for all intents & purposes as a thermocouple.

Typically for the safe area the output from one of these barriers would be 0-10Vdc or 4-20mA.

I would still sit down and read the NEC article 504 if you are not familiar with it.

Darren

 

[David_Emmerich]

I used a bank of their "Snake eye " IR T/C units a few years ago in a PET reheat oven ...They worked really well, were easy to use, and preformed better than I expected.
David

 

[awillms]

NEC Article 504 and others

Does anyone know if there is a website where I can get a copy of NEC Article 504 as well as ANSI/ISA RP 12.6-1995, ANSI/UL 913-1997. I know there are places you can purchase these, but if I just need a copy to read this one time, I would like to just be able to see what they say.

Thanks for any and all help you can provide.

awillms