# Difference between PT100 probe & thermocouple



## agillies (1/5/14)

Hi all,

I have been getting some great advice on this forum, hopefully someone might be able to answer yet another question.

I have recently purchased a few of the Sensos brand PID. (thanks QldKev, would have bought the wrong model if not for your advice).

Now i'm on the hunt for a probe.
What is the difference between a probe and a thermocouple? more so, is one better than the other?
The probes seem to be cheaper, but would need to buy a thermowell to i suppose.

I have noticed a few people recommend the Auber deluxe, is that still the one to get? or are there cheaper versions that are as good?
Any places people recommend to buy them from?

Thanks

Adam


----------



## djar007 (1/5/14)

The thermocouple is the working part . There are thermocouples and thermowells to put them in. Probes are for aliens.


----------



## agillies (1/5/14)

djar007 said:


> The thermocouple is the working part . There are thermocouples and thermowells to put them in. Probes are for aliens.


is one better than the other?
I have a spare thermowell, but if its not as accurate then i'll just get thermocouples.


----------



## djar007 (1/5/14)

Usually the thermo well is just a place to put the thermocouple. Some thermocouples are placed in a stainless tube and finished with a glue or resin or heat sink paste. If using a thermo well it is common practice to use a heat sink paste to fill the void and help with accuracy.


----------



## verysupple (1/5/14)

Just to be clear, a thermocouple is a _type _of temperature sensor. i.e. different to a thermistor or an RTD or a thermometer etc. A thermowell is just a heat conducting fitting used to protect a temperature sensor. 

I'm not familiar with that particular PID controller, but depending on the design of the thermocouple you get, you may or may not need to use a thermowell. If it's sealed, waterproof and can handle the temperature range you need then you won't need a thermowell as the thermowell simply protects the sensor. If it doesn't need protecting, don't bother.

Edit: BTW, a PT100 is an RTD. Thermocouples and RTDs work in different ways so it's unlikely your controller will be able to use both types. You better check what kind of sensor your controller needs.


----------



## 431neb (1/5/14)

Spudfarmerboy posts on this topic in this thread. Not heaps of info but an enjoyable thread nonetheless.

http://aussiehomebrewer.com/topic/76055-all-grain-3v-electric-system/


----------



## agillies (1/5/14)

verysupple said:


> Just to be clear, a thermocouple is a _type _of temperature sensor. i.e. different to a thermistor or an RTD or a thermometer etc. A thermowell is just a heat conducting fitting used to protect a temperature sensor.
> 
> I'm not familiar with that particular PID controller, but depending on the design of the thermocouple you get, you may or may not need to use a thermowell. If it's sealed, waterproof and can handle the temperature range you need then you won't need a thermowell as the thermowell simply protects the sensor. If it doesn't need protecting, don't bother.
> 
> Edit: BTW, a PT100 is an RTD. Thermocouples and RTDs work in different ways so it's unlikely your controller will be able to use both types. You better check what kind of sensor your controller needs.


This is starting to make sense now.

Some of the description on ebay confused me.

the link below is what i'm probably gonna look at getting.
http://www.ebay.com.au/itm/RTD-Pt100-Temperature-40mm-Probe-with-1-2-BSP-Thread-SS316-Beer-Brewing-/181284044118?pt=AU_B_I_Electrical_Test_Equipment&hash=item2a355efd56

It definately takes an RTD, as I was looking at K type ones, until i was told they aren't as accurate.

Do you know of any good suppliers of PT100's?


----------



## verysupple (1/5/14)

agillies said:


> This is starting to make sense now.
> 
> Some of the description on ebay confused me.
> 
> ...


Sorry, I don't know of any good suppliers, I just know the science behind how stuff works. 

Can you post a link to the specs or user manual of the controller you have? I then might be able to recommend a sensor, or at the very least what type you need.

Or you could just ask QLDKev as it seems he uses them.

Edit: I misunderstood part of what you wrote, but I get you now.


----------



## barneyhanway (1/5/14)

PT100 is what you need and Auber have the best ones.
You can get a 1/2"NPT thread model to go into your plumbing (typically for a recirculating system) or a weld-less model to fit directly into your vessel. 
The deluxe cable option is well worth paying the extra for if you're fitting the PID into a cabinet as the deluxe cable comes with a cabinet mount fitting and is then removable at both ends.
You can get 1/2" NPT ones cheaper from eBay if you look hard but not with the deluxe cable. Best to just pony up for an Auber in my opinion.


----------



## QldKev (1/5/14)

barneyhanway said:


> PT100 is what you need and Auber have the best ones.
> You can get a 1/2"NPT thread model to go into your plumbing (typically for a recirculating system) or a weld-less model to fit directly into your vessel.
> The deluxe cable option is well worth paying the extra for if you're fitting the PID into a cabinet as the deluxe cable comes with a cabinet mount fitting and is then removable at both ends.
> You can get 1/2" NPT ones cheaper from eBay if you look hard but not with the deluxe cable. Best to just pony up for an Auber in my opinion.


100% agree with this. I tried a couple of eBay ones, I've replaced the lot with the auber deluxe ones. The quality can't be beat and being able to drop the cable both end for cleaning is a bonus.


----------



## agillies (2/5/14)

Thanks for all your posts,

have ordered the auber deluxe ones.
To say my missus was unhappy is an understatement, she's now off to Mimco to buy a new handbag. Ouch. Lol


----------



## agillies (5/5/14)

Just for the viewers at home-
after I ordered the Auber probes, I had a look on Aliexpress and was kicking myself as i found what looked like the Auber probes.
http://www.aliexpress.com/item/SS316-beer-brewing-liguid-temperature-sensor-with-1-2-BSP-thread/1653180771.html

until I read "Class B. +/-0.30C at 0.0 C", the Auber ones are Class A +/-0.15 at 0.0 C.

Moral of the story, follow senior (i mean experience, not age) brewers' advice on this site. I maybe spent and extra $50 and got the quality I need.

Cheers for everyone's help

Adam


----------



## vr4king (5/5/14)

PT100's are based on resistance and TC's are based on mV with a compensating reference junction, My job is to calibrate these thing day in day out........For a basic Brew setup a TC would be sufice but a PT100/RTD will be far more accurate over a bigger temp range, If your focusing on a narrow temp range then you should be able to put a "offset" into your TC reader to correct it....A simple way to get a true known temp is to make a good "ice point" by shaving store bought ice and then wetting it with tap water.....This will get you within +0.01 to -0.01 degC then you can tune in an offset from this as I did with my ST-1000 then I chcked it at some common ferment temps and found it to be spot on BUT ST-1000's use a thermister which is a postive co-effencient resistor so that different again

Another thing to note is you CANT extend a T/C lead without using the original T/C type cable and any join will have a huge effect on it....Where a RTD is fine as its just resistance measured and normally at a minimuin they are 3 wire RTD's that dont take cable resistance into account.....

If cost is no worry then you cant go past an undamaged/corrected RTD,But i feel a good decent T/C is fine foe brewing........Hope this helps

Oh to ensure your T/C's stay good DO NOT kink the lead etc.....sorry for bad spelling


----------



## booargy (5/5/14)

vr4king said:


> PT100's are based on resistance and TC's are based on mV with a compensating reference junction, My job is to calibrate these thing day in day out........For a basic Brew setup a TC would be sufice but a PT100/RTD will be far more accurate over a bigger temp range, If your focusing on a narrow temp range then you should be able to put a "offset" into your TC reader to correct it....A simple way to get a true known temp is to make a good "ice point" by shaving store bought ice and then wetting it with tap water.....This will get you within +0.01 to -0.01 degC then you can tune in an offset from this as I did with my ST-1000 then I chcked it at some common ferment temps and found it to be spot on BUT ST-1000's use a thermister which is a postive co-effencient resistor so that different again
> 
> Another thing to note is you CANT extend a T/C lead without using the original T/C type cable and any join will have a huge effect on it....Where a RTD is fine as its just resistance measured and normally at a minimuin they are 3 wire RTD's that dont take cable resistance into account.....
> 
> ...


If you join a thermocouple cable doesn't one join cancel the other out so long as it is in the same enclosure (same temperature)?
thermocouples can also wired in series to give an average temperature. so one in the top and one in the bottom of the HLT would this make the control hunt the setpoint.


----------



## 431neb (5/5/14)

I looked at the Auber instruments website and got a little confused on postage and wether I was buying the sensor and the deluxe cable so I started googling.

Can anyone confirm the suitability if the following item...

http://m.alibaba.com/product/1349020701/PT100_RTD_with_compensation_cable_1.html


----------



## schrodinger (5/5/14)

booargy said:


> If you join a thermocouple cable doesn't one join cancel the other out so long as it is in the same enclosure (same temperature)?
> thermocouples can also wired in series to give an average temperature. so one in the top and one in the bottom of the HLT would this make the control hunt the setpoint.


RE joining: yes, if you're using the same type of cable (e.g., copper for one lead, constantan for the other). But an uninformed user might think they could extend the wire with ordinary Cu/Cu wire.

RE thermocouples in series: did you mean in parallel? If in series, the intervening junctions would all need to be at the ref temp. Easier to achieve by 'splitting' the tc line into multiple lines out to the multiple junctions. Or am I missing something?

RE the broader question of thermocouples vs RTDs: I previously argued for the former, but for the price of PT100s these days, it's a no-brainer. But still, my experience has been that type T thermocouples don't drift significantly.


----------



## booargy (5/5/14)

schrodinger said:


> RE joining: yes, if you're using the same type of cable (e.g., copper for one lead, constantan for the other). But an uninformed user might think they could extend the wire with ordinary Cu/Cu wire.
> 
> RE thermocouples in series: did you mean in parallel? If in series, the intervening junctions would all need to be at the ref temp. Easier to achieve by 'splitting' the tc line into multiple lines out to the multiple junctions. Or am I missing something?
> 
> RE the broader question of thermocouples vs RTDs: I previously argued for the former, but for the price of PT100s these days, it's a no-brainer. But still, my experience has been that type T thermocouples don't drift significantly.


It took me a while to find someone who could explain how different temperature sensors work. So I was just trying to get a bit more information out about how they work.
for me I will be upgrading to digital DS18B20 temp sensors and they are cheaper again.


----------



## old mike (30/5/14)

Thermo couple cables are usually a single strand Stainless steel wire which are virtually impossible to join to extend, so its important to order a cable the lenght required. RTD PT100 use 100ohm cable, hence the "100". yes its correct that these can be extended, but all 3 cables should be 100ohms resistance. Thermo couples will react to change faster, but RTD PT100 sensors are more accurate


----------



## billygoat (30/5/14)

old mike said:


> Thermo couple cables are usually a single strand Stainless steel wire which are virtually impossible to join to extend, so its important to order a cable the lenght required. RTD PT100 use 100ohm cable, hence the "100". yes its correct that these can be extended, but all 3 cables should be 100ohms resistance. Thermo couples will react to change faster, but RTD PT100 sensors are more accurate


Not quite right.
Thermocouples can be extended using either extension or compensation wire. The wire is made from the same material as the thermocouple.
Example - If its a Type K thermocouple, the wire will be made from Chromal and Alumel.
They dont use stainless steel wire.
PT100's can be extended using copper wire. Its not the wire or cable that has a resistance of 100 ohms, the PT100 will measure 100 ohms at zero degrees, but only between the actual resistance sensor. If you measure resistance between the two common wires you will get close enough to zero ohms.


----------



## PaulAndrews (12/10/16)

Pt100 is a Platinum RTD (Resistance Temperature Detector) with a resistance of 100 ohms at 0°C which changes with temperature. They are suitable for applications in the temperature range of -200°C to 600°C but are more commonly used in the range -50°C to +250°C, for instance water cooling, oil cooling, refrigeration, food processes and at ambient. These temperature sensors are reliable and can offer a higher degree of accuracy.

Check out the thermocouples on Pyrosales.


----------



## sp0rk (12/10/16)

Dug up a 2 year old thread to explain something already explained and spruik a website?
Sounds fishy to me


----------

