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Old 06-05-2010, 05:37 PM   #1
tokolosh
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Default RTD calibration.... difficulties.

So I recently made a pipe-bomb-looking RIMS. I'm using the 2" liquid tight RTD probe from Auberins.com coupled with the SYL-2352 PID. My issue is that my temp readings are off. Not way crazy off, just off enough to not trust it.

I've read through the other threads and know I have the correct input type selected in the Sn setting and I'm aware of the offset allowance in the Pb setting.

The issue is that it's reading approx 3-4 degrees higher than my other thermometers in the crushed ice water test and 6-7 degrees lower in boiling water. WTF????

I called Auberins on it and the only suggestion they had was maybe there wasn't enough thermal compound and I should disassemble the probe and add more. Which didn't really sit well with me, it kind of sounded like they made a product that didn't work and i should fix it...

Anyway, thought I'd see if anybody here had any good ideas! I appreciate anyone's help!

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Old 06-05-2010, 06:19 PM   #2
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Are you sure your other thermometers are correct? A man with two clocks and all that.

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Old 06-05-2010, 07:29 PM   #3
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The PT100 RTD's can have different resistance slopes, the probe and SYL-2352 might have different resistance slope factors that are giving you those results. The competively priced units do not have the flexibility to choose the slope factor so you will have to split the difference and live with it, or look for another RTD sensor with matching resistance slope.

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Old 06-05-2010, 08:55 PM   #4
tokolosh
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I have tested it with both digital and a regular glass thermometer...

Quote:
Originally Posted by kladue View Post
The PT100 RTD's can have different resistance slopes, the probe and SYL-2352 might have different resistance slope factors that are giving you those results. The competively priced units do not have the flexibility to choose the slope factor so you will have to split the difference and live with it, or look for another RTD sensor with matching resistance slope.
Hmmm.... slope factor. Never heard of that before, in the manual it has this under the specs (forgive me, I'm an idiot about this stuff):

Input type:
Thermocouple: K, S, WRe (5/26), T, E, J, B, N
Resistance temperature detector: Pt100, Cu50,
DC voltage: 0~5V, 1~5V, 0~1V, -100~100mV, -20~20mV, -5~5V, 0.2~1V.
DC current (external shunt resist needed): 0~10mA, 1~20mA, 4~20mA

Is it the resistance temperature detector #s that I should be matching up?
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Old 06-05-2010, 09:34 PM   #5
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Quote:
Hmmm.... slope factor. Never heard of that before,
Check with the supplier what RTD is required, with European curve element (alpha = 0.00385) or US, etc.



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Old 06-05-2010, 10:32 PM   #6
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PT100 RTD sensors are available with 2 different calibration curves, 0.00385 ohms is known as DIN or european and 0.003916 ohms is known as JIS. most pid controllers can use both and have a configuration parameter to select which curve to use, but i looked at the auber documentation for the SYL-2352 and it appears that this pid doesn't allow you to select a curve... i would assume that since auber sells RTD's with DIN curves that their pid controllers should work accurately with them? fwiw, i've used several auber RTD's with watlow, omron, barber coleman and red lion controllers and have never had any calibration or accuracy issues with any of the sensors. i'm wondering if your calibration issue is caused by your SYL-2352 controller?

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Old 06-05-2010, 11:33 PM   #7
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+1 on RTD accuracy, that's why they are so popular because their output is pretty close to linear, especially in the 0-100C range.

if you have a decent multimeter you could do this to see if the RTD or the pid is the problem.

in ice water you should measure close to 100 ohms across the + and one of the minuses. at boiling it should be 138.5 ohms.

If it was a thermal compound it would get to temp eventually. RTDs are slow responding, you are giving it a little time right?

If you find the probe or PID is out of cal then ask them to replace it, they are usually pretty good about it.

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