Temperature Sensor Type 1

[lukin1977]

I have to install a new temperature controller to a new tank that has to be heated with a electric resistance
The temp sensor has 3 cables: 2 white, 1 red
The seller of the tank is not responding

At first I thought that the sensor was a thermocouple but I am not sure because TC usually have only 2 cables

Any help on identifying what type of sensor do I have? Is it a RTD?

 

[btrueblood]

Yes, it looks like a 3-wire RTD. Check the resistance between the wires, one pair should be a near short circuit. But that may or may not help you much, as you also need to know the material (platinum, nickel/chrome, ...?) to know the temperature coefficient.

 

[lukin1977]

R white_red=113,5 ohm
R white_red=113,5 ohm
R white_white=2,5 ohm

I am guessing is a Pt100

 

[xnuke]

It's probably a Pt100, since Ni tends to have a 120 Ω base resistance. However, as btrueblood pointed out, you still don't know if it's a Pt100-385 or a Pt100-392.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[itsmoked]

I concur with the 3-wire 100 Pt.

The whites are common, tied together at the RTD. You will need a 3-wire RTD controller. A symbol on the controller usually shows the schematical hookup clearly.

Then choose one of the two standards (US or European) and using an accurate thermometer at two different tank temps see if your guess was right.

Also consider what happens the day the electrical heaters stick ON, as it will happen someday. If the result can be destroyed product, burned animals(humans included), poison emissions, or fire, include an electrically separate second temp monitor/alarm/cutout.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[xnuke]

Odd wire colors, though. The standards for industrial platinum resistance thermometers (ASTM, IEC) indicate 3-wire color code is supposed to be red, red, white.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[moltenmetal]

Odd colours possibly because it appears to be Teflon-coated wire. The unit is immersed in an FRP tank and that looks like a PFA-coated heater element in the picture too- a plating bath or something else containing corrosive material.

 

[lukin1977]

As moltenmetal said; Tank is FRP and heaters are PFA-coated.
Tank will be filled with H2SO4 (20% in water)
Process temp will be 75 ºC

Already bought the controllers with Pt100 / Cu50 / TC sensor input

Thanks to all

 

[John2025]

I'll second Keith's warning. At some point, something is going to fail in the ON position, it's just a matter of when.
Boiling Sulfuric sounds really bad.

 

[lukin1977]

Can you recommend a fail safe system with out the need of a redundant temp sensor?
The controllers I have have 2 alarms (relay outputs) configuration which I can use to open a main contactor installed before the process contactors if temp reach a set value

 

[moltenmetal]

Correct me if I'm wrong, but I believe RTDs fail to the high temperature when they go open circuit just like thermocouples, ie a wire corroding off, so that should be OK. If not, you've just reinforced yet another reason in my mind to avoid them when their extra temperature accuracy over a thermocouple is not required.

I do suggest that if you're using a solid state relay or other semiconductor device to turn the heater on and off, that you have a good old fashioned mechanical contactor upstream of that device which is interlocked to open the heater circuit on a high high alarm. You have the alarm contacts to do that easily. All the semiconductor devices have at least some probability of an on-state failure, and if I remember correctly there is an electrical code requirement for such an interlock on process heaters for this reason. I could be wrong on that, but know that it is widely practiced and a very good idea to do, codes or not.

 

[moltenmetal]

What I'm saying here is that the 2nd temperature measurement device and separate alarm trip module that are sometimes used on heaters, are not absolutely required in this case- all you need is the contactor interlock to eliminate the risk of on-state failure of the TY device which controls the heater. If the RTD fails low when it goes open circuit, or the consequences of a failure are dire, i.e. your FRP tank will melt and de-inventory all over unsuspecting people if the acid were to boil for a while (unlikely in my view), then the complete duplicate interlock system would be warranted.

 

[danw2]

>Can you recommend a fail safe system with out the need of a redundant temp sensor?

No. Good practice and codes universally require a separate 'controller' to drop out the energy supply in heating apps.

Using an alarm on the primary controller carries the enormous risk of common mode failure.

See NetNathan's post on this thread:

Link

http://www.plctalk.net/qanda/showthread.php?t=97338&highlight=personal+story

 

[moltenmetal]

Danw2- enormous is a big word. Lots of commercial heating devices ignore your advice.

The number and robustness of layers of protection required to make something adequately safe depend both on the probability of the failure and the severity of the harm caused. The likely outcome of a fail on heater in an FRP tank is the failure if the heater coating leading to a rapid failure of the heater sheath, with the resistance wire going soon after that. That's a view from a distance though, and if the harm is likely to be more severe, the 2nd temp sensor and alarm trip module are warranted. But they are not absolutely required on every single heating application- that is an incorrect statement of fact.

 

[John2025]

If was in my facility, I think I'd fill the system with plain water and run it full blast to see what temp it tops out at. If it doesn't get too hot, I'd be satisfied with an auxiliary contactor run through the alarm. FWIW, in my years in a plastics processing plant I've seen a lot of runaway temps. The consequences for us are usually minor, but we did have one runaway on a system with a higher watt density that melted the heater assembly into a puddle of aluminum before it shorted. I agree with the FMEA approach.