Accurate RTD PT100 sensor

[Fidelity101]

I have 4 RTD PT100 sensors in my system and they're all giving me temperature measurements that jump around 1-2F which makes it difficult to dial in my PID's. I checked the ohm's of each sensor and everyone seems to be jumping around which makes me think they're not accurate enough for what I need. I believe they're class B.

What I am looking for is class A or class AA with a QD plug and setup to attach to my 1.5" TC port. Has anyone found a source of quality probes?

https://ebrewsupply.com/products/rt...45455&pr_ref_pid=4477252370522&pr_seq=uniform

I emailed these guys yesterday to ask what class the sensor was and I haven't heard back yet. They're twice the price of the sensors I currently have so hopefully they're at least class A.

 

[Deadalus]

What brand sensors do you currently have?

 

[Deadalus]

The one you linked to says the probe itself is mounted into the TC fitting using 1/2" NPT. Is the inside part of the TC fitting a thermowell, seems so? I don't know about the seal, it may just be a gasket, but it seems like you might be able to get a 1/2" NPT sensor and save the cost of the TC fitting that it is attached to. That would be if your current sensor that you want to replace is similarly configures. My sensors are all NPT so I am not sure about how the TC ones are built exactly.

 

[Fidelity101]

These are the sensors I have right now.
https://spikebrewing.com/products/tc-temperature-probe

According to Spike, they are class B. I have 4 of them and all 4 oscillate in resistance from .1 to .2 ohms which changes the temperature reading by 1-2 degrees. From the research I've done so far, I think class A would be ideal as class AA would be cost prohibitive. I have another 1.5" TC fitting with a 1/2" NPT thread so I might give that a shot if I can find a reasonably priced class A probe. I wish someone from ebrewsupply would respond to emails as that would definitely be worth the asking price if it was class A.

 

[Broken Crow]

with a QD plug

This ^ will likely give you a problem. I have a real bug up my a** about standards and manufacturers ignoring them...
I don't what a 'QD' plug for a temp sensor is but my gut tells me you are unlikely to find a probe with the same connector from an alternate vendor. If you're prepared to make modifications to accomodate for a different connector, I heartily recommmend the Auber probes: https://www.auberins.com/index.php?main_page=index&cPath=20_131_15
I've bought various probes from various sources and it's a crap-shoot. I finally shelled out for Aubers and have no regrets; each of the 3 Auber probes give the exact same reading in both the ice-water and boiling water tests while probes from other vendors, including identical ones vary.
Just sayin'

 

[Thorrak]

Unfortunately, I'm pretty sure that Spike is just selling rebranded ElectricBrewingSupply sensors -- but I'm holding out hope that this isn't the case!

The QD plug is just Mini XLR. I would imagine that either Spike or ElectricBrewingSupply should have the pinout. Might require some soldering, but should be straightforward.

 

[Fidelity101]

Thank you! The temperature probes themselves (from Spike) are giving the ohm resistance changes before I even connect the QD but I'm sure the QD plug isn't helping. I'm going to give these a shot!

 

[psehorne]

FROM Auber https://www.auberins.com/index.php?main_page=product_info&cPath=20_131_15&products_id=26
Class A

 

[Thorrak]

XLRCON-M appears to be exactly what spike uses

Edit: I just ordered one of those @psehorne linked with the XLRCON-M cable. I'll be curious to see how it goes!

 

[Fidelity101]

I purchased two of them. One standard length and one with a 6" probe as I'm trying to get more accurate temperatures from my Spike HERMS system. It's a seperate issue but even with the pump running, the center is 4F higher than the sides and I am having trouble dialing in my PID...which put me down this rabbit hole of finding more accurate sensors.

 

[Deadalus]

I didn't kniw there were standards for these so good to know. I briefly looked that up and I saw there was the ohm test at a specifed temp. But where I saw that the test temp was 0C.

I have three Auber NPT sensors. Good to know there are standards for testing. I was having trouble with one of mine last year. It seemed more llike the female connector was jostling the connection and causing fluctuations. I replaced the connector (soldering). I may be having trouble with it again so good to know about ways to test.

My newest probe, the third, has slightly better connection pins than the first two, with the problematic probe being one of the two. I will post the differences in cables when I get a chance.

 

[Indian_villager]

What are you measuring when you are getting the temperature fluctuations? Is it in air, is it in a kettle full of water, are you in an ice bath? Have you confirmed your grounds work well? Are you getting good continuity across the loop run? Are you seeing fluctuations in the loop run?

 

[Fidelity101]

The measurement is in a 20 gallon hlt brought to 180F with 15 gallons of water and then let alone with the pump flowing for a few minutes so the temp settles out. The measurement was taken from the plc pins and then the end of the cable attached to the probe and finally the probe itself. The fluctuation is coming directly from the sensor and doesn’t seem to vary from the probe itself all the way to the plc readout.

 

[Indian_villager]

These measurements are while the pump is circulating? Just trying to consider if there is a potential for stratification or some other current.

 

[Fidelity101]

I see that could be a concern so I turned the pump off and let it sit for 5 minutes. I did expect it to drop given it was hotter than room temperature. The problem was that it was jumping all over the place so heat layers wouldn't really explain the problem.

I have new sensors on order so I'll be able to compare sensors once they're installed. The other variable causing me confusion is that the spike solo brew system used this exact sensor and it was dialed in perfectly. I think it's a combination of the sensor jumping around AND possibly the more accurate and more frequent updates on the industrial PLC system that I'm using.

 

[Fidelity101]

I tried Spike, Auber, some cheap option from Amazon and a very expensive probe from a commercial application.

UPDATED: These sensors reported zero delta because they were not wired correctly. The wire outputs are different than every other sensor so the values were not valid.

https://www.amazon.com/dp/B09MP3ZZP5

Spike changed by 0.4 ohms. Auber and the commercial sensor changed by 0.2 ohms which makes sense as class B is suppose to be half as accurate as class A. Every sensor I tried was at room temperature and connected to the same metal block and all reported the exact same resistance...at least in the same range.

I'm going to have to go back into my ladder logic with the automation direct PLC to see what this resistance delta reduction does to my temperature fluctuations but I thought I'd give you guys an update.

 

[Ozarks Mountain Brewery]

keep in mind the probes might not be the issue, it could be the wiring or even soldering issues

 

[Climb]

@Fidelity101 - Does the PLC do any averaging of temperature readings before updating a temperature display or using the temperature in it’s control logic? If not, is this something that you could add to the PLC logic? Asking as I have never worked with a PLC.

A simple moving average is a low pass filter and should help smooth out the temperature fluctuations and reduce signal noise from the sensor that you are concerned about.

How accurate is the meter that you are using to measure the resistance of the sensors? Are you sure the resistance jitter is coming from the sensor and not the meter?

 

[Fidelity101]

That's a great idea that my PLC programmer already incororporated. I'll attach the file in case anyone wants to take a look. Basically, we average out the readings over 5-10 samples and then push that to the PIC and on the screen. The massive temperature swings are just not able to be absorbed by averaging. I think Ozarks Mountain Brewery is on to something and I'll have to explore the exact input that the PLC is getting from the card itself while looking at the temperature readings. Something is definitely crazy...maybe it's my programming.

 

[Fidelity101]

I spent all day trying to figure out what's going on. Replacing the Spike sensors with class A sensors from Auber cut the fluctuations in half but they're still there. Even putting in a resistor allows the temperature to fluctuate 0.3 degrees over a given time period.

The Auber sensors matched the results of a very expensive commercial grade sensor borrowed from work. Their quality is well worth the price!

The temperature fluctuations seem to increase the longer the system is left on...which just adds another layer of confusion for me. I started the day dialed in within 0.5F and by the end of the day it was around a 1.2F delta.

Any ideas?