Heat Trace - Correct RTD Placement

Are you heating the pipe/vessel for freeze protection or to maintain product temperature?

How you answer will dictate where you mount the RTD.

For freeze protection, mount the RTD to detect un-adulterated ambient temperature.

To maintain product temperature, mount RTD on pipe/vessel.

You can also call the HT manufacturer or manufacturers rep. They are usually very helpful in pointing you in the right direction.

This link is very limited and generalized: http://www.tycothermal.com/assets/NorthAmerica/English/Documents/Installation_Operation_and_Maintenance_Manuals/Products/476/H56998_RTD200_II_0203.pdf

Thanks, I am concerned with freeze protection on pipes currently. Is the RTD mounted on the pipe or near the pipe? The link you provided showed the RTD with a lead wire, does this run back to the power kit or to the controller? I do not have a vendor, as I said I'm just a student of heat trace for now. Thanks.

Hubbard,

As stated in my previous reply, for freeze protection mount RTD where it can detect un-adulterated ambient temperature (EDIT) where freeze protection is desired.

If you have a controller, run an RTD extension lead back to the controller as well as the power connection kit leads (power).

If no controller, you can run the RTD lead to the power connection kit provided the kit has an RTD input. Some power connection kits come with an integral RTD (depending on manufacturer) at which point you do not need a separate RTD (in fact this type usually comes with an armor covered RTD to protect the RTD from damage).

Hopefully you are aware that you CAN NOT connect the RTD element directly to heat trace line voltage to control it.

KJK/USA,

Thank you for your reply. Yes I am aware that you cannot connect the RTD element directly to heat trace line voltage to control it.

I am also aware that you need to put the RTD in a place that will be useful in determining the ambient temperature around the pipe you are considering.

Does there need to be a minimum distance between RTDs or is it dictated only by circuit length? Is only one RTD needed per freeze circuit? Are the RTD's typically placed at the end or the beginning of the circuit (say they are within 100 feet of each other) or does it matter? I see they are fed by conduit. Are the RTD's typically mounted on a wooden apparatus near the pipe? I'm guessing they are not mounted on anything metal as that would probably interfere with a correct temperature reading?

~Hubbard

KJK/USA,

Thank you for the information. I have not done a heat trace project myself but I think the technology is interesting. I am learning in case I decide it is something I would like to get into. Usually when you are on a project you do not have time to figure out these little details. It is good to know the vendors are so willing to help with design.

Regards,

~Hubbard

I think you guys may have been a little harsh Here

I would assume that RTD's are similar to 2 wire thermocouples. some controllers are going to require ungrounded units, others more forgiving. From what I know most RTD's are 3 wire, using a resistor to stabilize the output. I know when I worked at the bakery, we actually got longer service using Bi-metal thermocouple wire twisted together, instead of bayonet mount J-type. This had more to do with the ability to visually assure good contact with a large chunk of hot metal

Were I doing heat trace to keep pipes from freezing I would stick with the self regulating stuff.

At least Hubbard bothered to register & login

Thank you Garthh.

My speciality is in Cathodic Protection, but what I have learned so far about RTDs, I would agree with what you have described.

I will take into consideration what you recommended about the self regulating HT. Thanks again.

Does it matter? Just because I don't have a current practical application doesn't mean I will never do a heat trace design.

I don't see anything saying this is a forum just for people doing actual work in lieu of wanting information. You can't do an actual design until you learn how in the first place.

Seeking academic knowledge is a waste of others' time? Good to know. I'll make sure to qualify the question next time.

An RTD requires a transmitter, cabling, a power supply, a trip-amplifier and a contactor to switch the trace heating on and off.

Self-limiting trace heating tapes don't require temperature sensing and switching. They stay on all the time and the power load is self-regulated to maintain the desired temperature.

Thank you both very much for your helpful comments.

Carl E, the diagram that you provided really lays it out for me, thanks.

Normally you put RTD where there is no temperature interferences which could be caused by other heat sources, or heat sinks such as pipe supports, valves, etc.