Just about to place the order for the PID and was wondering if anyone uses the K Type thermocouples. Do you find them to be not that accurate? Its hard to drop $65 for 2 RTDs when K type go for less then $10 on ebay.
K type thermocouple or RTD sensor
- Thread starter acefaser
- Start date
Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:
samc
Well-Known Member
RTD !
I've used both and find RTD's to be more accurate. I also like to stick with the same source for both devices. I've found that the calibration is usually pretty close as delivered, whereas when I've bought other brands I have to work at it.
I've used both and find RTD's to be more accurate. I also like to stick with the same source for both devices. I've found that the calibration is usually pretty close as delivered, whereas when I've bought other brands I have to work at it.
You can get liquid-tight RTDs for under $10 on ebay, too:
http://cgi.ebay.com/Thermocouple-Te...528?pt=LH_DefaultDomain_0&hash=item3cb7542018
http://cgi.ebay.com/Thermocouple-Te...528?pt=LH_DefaultDomain_0&hash=item3cb7542018
Probably because they mistakenly labeled them as "thermocouples" and don't mentioned "RTD" in the listing.
I actually searched for "pt100", which is a common type of RTD, and that's what showed up.
Thermocouples can be very accurate. We use them in the lab all the time, in fact i can't think of a temp probe that isn't a thermocouple that we use on a daily basis.
I think that in our context here (homebrewing) the problem is that many of us need to extend the leads on our temperature sensors or put them through a wall of some sort (control panel side, etc) using a disconnect. In these cases you have other issues to contend with such as matching wires and proper connectors with thermocouples. These aren't problems for RTD sensors.
As Walker said, though, you can get RTD's for about the same price point as thermocouples. You sacrifice some temperature range going with RTD's, but again in this context they really have no significant limitations and a host of benefits.
I think that in our context here (homebrewing) the problem is that many of us need to extend the leads on our temperature sensors or put them through a wall of some sort (control panel side, etc) using a disconnect. In these cases you have other issues to contend with such as matching wires and proper connectors with thermocouples. These aren't problems for RTD sensors.
As Walker said, though, you can get RTD's for about the same price point as thermocouples. You sacrifice some temperature range going with RTD's, but again in this context they really have no significant limitations and a host of benefits.
samc
Well-Known Member
excerpted from here
Selecting sensors for reliability
For temperatures ranging from cryogenic to about 800°F (427°C), a resistance temperature detector (RTD) is better than a thermocouple. Though RTDs were once more expensive, today the cost difference between the two is negligible, and an RTD provides greater accuracy, stability, and life span. Over its useable range, a standard-grade RTD provides more than twice the accuracy of a thermocouple.
To understand why, consider the materials of construction. A thermocouple is comprised of two dissimilar metals welded together; the resulting junction begins to deteriorate immediately. The deterioration is faster at higher temperatures and can result in drift of several degrees per year. On the other hand, an RTD consists of stable, highly purified platinum.
RTDs drift just fractions of a degree per year and are accurate for many years when used at temperatures below 800°F (427°C). Thermocouples, however, are not and require frequent replacement. This tips the scale for installation costs in favor of the RTD.
Selecting sensors for reliability
For temperatures ranging from cryogenic to about 800°F (427°C), a resistance temperature detector (RTD) is better than a thermocouple. Though RTDs were once more expensive, today the cost difference between the two is negligible, and an RTD provides greater accuracy, stability, and life span. Over its useable range, a standard-grade RTD provides more than twice the accuracy of a thermocouple.
To understand why, consider the materials of construction. A thermocouple is comprised of two dissimilar metals welded together; the resulting junction begins to deteriorate immediately. The deterioration is faster at higher temperatures and can result in drift of several degrees per year. On the other hand, an RTD consists of stable, highly purified platinum.
RTDs drift just fractions of a degree per year and are accurate for many years when used at temperatures below 800°F (427°C). Thermocouples, however, are not and require frequent replacement. This tips the scale for installation costs in favor of the RTD.
mcwilcr
Well-Known Member
Well, I can agree with this in theory but I can also tell you in practice, in any lab setting I have ever been in and I have been in allot, thermocouples can last a very long time and because they have a very predictable response curve they are very easy to calibrate initially and when they do drift out of cal over time.
That being said, trigger is right about the potential issues we may see in homebrewing and if the RTD will work better for your setup then you should certainly go that rout!
OP
OP
acefaser
Well-Known Member
I think I am going with the RTDs for the following reasons:
1. I'm anal and strive for perfection and the RTDs are more accurate.
2. The Auber Instrument RTDs have the nice quick disconnect to remove the wire. (even though they are charging me $18 to ship something that would easily fit in a $10 USPS box).
I plan on using 1 PID and having the quick disconnect I could swap the wires from the HLT RTD to the RTD on the boil pot.
1. I'm anal and strive for perfection and the RTDs are more accurate.
2. The Auber Instrument RTDs have the nice quick disconnect to remove the wire. (even though they are charging me $18 to ship something that would easily fit in a $10 USPS box).
I plan on using 1 PID and having the quick disconnect I could swap the wires from the HLT RTD to the RTD on the boil pot.
Charlie_in_TX
Member
ace, you can use a compression fitting to mount the probe. something like http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053
PS - I have a couple Fluke temp meters. Thermocouple based. I have 1 of them re-certified to the NIST every 6 months. Part of the re-cert is a statment if adjustment was needed. In the 30 year range with no adjustments.
PS - I have a couple Fluke temp meters. Thermocouple based. I have 1 of them re-certified to the NIST every 6 months. Part of the re-cert is a statment if adjustment was needed. In the 30 year range with no adjustments.
OP
OP
acefaser
Well-Known Member
Using this with the Auber style probes? I'm confused how you could use the compression fitting.
I plan on using the electricbrewery design unless I can find a better/cheaper way and still have the quick disconnects to help remove the wires for cleaning the pots.
samc
Well-Known Member
The owner provides top notch service and is more than fair. I blew out 2 SSR's due to a *#$# EBAY purchased pilot lamp and Auber sold me new ones @ half price to help me overcome the sense of loss. The technical support is worth any extra costs over any EBAY overseas purchase !
BrewMoreBeers
Well-Known Member
Do you know what size the threads are on these? I need 1/4" npt.
I'm pretty sure it's 1/4" NPT, but better to ask the seller than me. 
I know this is ressurecting an old thread, but FYI:
At least I discovered all this on a $7 probe.
- While the thermowell is watertight, the whole unit is not. The threaded portion is tack welded on, but does not seal against the thermowell. You could use some silicone sealant to fix this (I would have done this in retrospect).
- The thread size is metric (M8). I have yet to find a way to easily screw this into NPT fittings (you could probably rig a weldless setup easily, but I was trying to add it to a sight gauge T). I was planning to use a compression fitting 'till I killed the probe trying to remove the threaded portion (...or possibly by testing it in water when it wasn't fully sealed). You can use some number 109 o-rings around the threaded portion and a compression fitting, or ignore it (or remove it carefully) and use some number 008 o-rings and a 1/4" compression on the thermowell itself.
At least I discovered all this on a $7 probe.
BetterSense
Well-Known Member
I would go with RTD over thermocouple every time. Thermocouples are only to be used when they are absolutely necessary (at high temperatures, or in low-cost applications).
Similar threads
