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[10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/10/2012 4:36 AM

Hello every body !

1) I want know if there is currently a solution for [ 10°C, 60°C ] temperature mesurement with accuracy of +-0,01°C.

2) is it possible to improve the performances of a sensor like pt100 or pt1000 with a signal conditionner in order to obtain the accuracy above ?

Thank you very much in advance .

Pathfinder Tags: accuracy pt100 RTD signal conditionner.
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#1

Re: [10°C,60°C] temperature mesurement with +-0,01°C of accuracy

08/10/2012 4:37 AM

A1) One solution is to review the need for such accuracy. 1/100 of a degree celsius? The specification sounds too tight to be meaningful.

A2) Unheard of. Pt100 RTDs are connected into a Wheatstone Bridge circuit, the balancing of which indicates the temperature to the rest of the circuitry. There is no need to consider the measuring device solo and disregard the rest of the equipment!

Consider the measuring device. It is a resistor. Current passing through it will dissipate heat, thereby affecting the measurement in a small way. There is an analog here with Heisenberg's Uncertainty Principle.

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#3

Re: [10°C,60°C] temperature mesurement with +-0,01°C of accuracy

08/10/2012 5:16 AM

1) the need for such accuracy is a real need expressed by some industrials. i have reached +-0,05 °C of accuracy using a pt100 and an ADDI-DATA´s msxe-3211 system. but it´s not enough . that´s why i have asked if it is possible to improve the sensor´s performances with a signal conditionner for example, and how much accuracy i will gain theorically with this. So the question is : how a signal conditionner improves the performances of an RTD and how to calculate theorically the accuracy gained usig a conditionner.

thank you

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#5

Re: [10°C,60°C] temperature mesurement with +-0,01°C of accuracy

08/10/2012 5:18 AM

Good luck with the quest. Reprogramming the industrials seems just as difficult.

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#11

Re: [10°C,60°C] temperature measurement with +-0,01°C of accuracy

08/10/2012 2:35 PM

It is possible to improve the resolution of a platinum probe with signal conditioning but there will always be consequences for doing this. To explain the consequences requires an understanding of sampling theory, uncertainty, thermodynamics, and phonons. All of these aspects will change with the media to be measured and the time period that one measures.

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#2

Re: [10°C,60°C] temperature measurement with +-0,01°C of accuracy

08/10/2012 4:59 AM

Do a google search for "Secondary SPRT -sport -sports -sort"

The -sport -sports -sort bits are to persuade google that SPRT is not a spelling mistake.

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#4

Re: [10°C,60°C] temperature measurement with +-0,01°C of accuracy

08/10/2012 5:17 AM

????

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#6

Re: [10°C,60°C] temperature measurement with +-0,01°C of accuracy

08/10/2012 7:47 AM
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#7

Re: [10°C,60°C] temperature measurement with +-0,01°C of accuracy

08/10/2012 8:04 AM

I've grown a little wary of direct links to google searches, because you get a location specific result: in our case google.co.UK.

I sometimes go to other countries google search pages like http://www.google.co.in , when I know where the OP is from, but, I haven't found out how to do a USA specific search because ".com" just defaults back to ".co.UK".

I am still a little perplexed by the OPs response.

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#15

Re: [10°C,60°C] temperature measurement with +-0,01°C of accuracy

08/11/2012 8:45 AM

Good point. Any idea whether lmgtfy changes the google locality when exported? Anyone?

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#18

Re: [10°C,60°C] temperature measurement with +-0,01°C of accuracy

08/11/2012 2:44 PM

Here's what I got, again in California:

This time I stretched the image out to pretty close to full page width. Does that make it easier or harder to read?

Dick

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#22

Re: [10°C,60°C] temperature measurement with +-0,01°C of accuracy

08/12/2012 6:57 AM

It's exactly the same result as I get (except for the "Placerville, CA"). This is more-or-less what Randall implied would happen - Google is the same in the UK and the USA.

Would be interesting to see what came up if someone in say South Africa or India tried it. The thing of particular interest is what appears in the address bar; in my case "http://www.google.com/search?btnG=1&pws=0&q=lmgtfy".

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#23

Re: [10°C,60°C] temperature measurement with +-0,01°C of accuracy

08/12/2012 9:35 AM

For whatever it may be worth, I'm actually in Fresno, about 170mi SSE of Placerville, this weekend.

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#17

Re: [10°C,60°C] temperature measurement with +-0,01°C of accuracy

08/11/2012 2:40 PM

That worked for me here in California. Here's a screen dump of most of the first page:

Dick

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#8

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/10/2012 1:57 PM

I'm having trouble coming up with any industry that could need that kind of resolution.

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#9

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/10/2012 2:14 PM

Protein crystallography requires a very stable temperature for single crystal structure growth.

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#10

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/10/2012 2:18 PM

Yes but, what are the odds that any of OP's "industries" are growing crystals.

I almost put a disclaimer in about analytical work, but decided not to bother.

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#12

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/11/2012 2:08 AM

The OP's question is confused, and he did not do due diligence in the subiect matter. IMHO.

1,. I do not believe, the need of even 0,01 degree measurement is necessary in chemistry or biochemistry anywhere. OP may believe so, but none of us would be alive, if that would be even approximately so. Biochemistry processes run fine with a +/- 0,2 degree, and so-so with a +/-1 degree. So, where did that requirement for high precision popped up from?

2,. IF Keithley or Fluke speaks of high precision measurement, expect to pay for it in gold. And expect it to work in a calibration lab, with trained technicians. Not with a biochemist, untrained.

3,. Now, if the good fellow would bother to talk about repeatibility, that would be a different issue. And I take the freedom to assume that.

4,. To run experiments in a highly repeatable fashion, one needs a thermostat within a thermostat. A single semiconductor diode fed by current delivers precise voltage in the 0,6V neighborhood. Dependent only on physics. Large enough to drive a comparator. But, your assumed precision will still need an awful amount of work.

5,. Once done, how want you to verify it?

6,. Now, If I completely misconstrued OP's question, a clarification is required. What I do not believe, that he can do better, than the big names in measurement. When something is compromised, something gotta give.

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#13

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/11/2012 7:49 AM

Here are a few pointers:

Self heating error is likely if the reference current is high and the coupling with the media is poor. Try to use a high thermal conductivity probe with a large surface in contact with the media. Reducing the current reference will reduce the self heating but also reduce the signal to noise ratio. Do it only in "quiet" environment.

The precision of your current reference is very important. Whether you use a current source or a Wheatstone bridge makes a big difference. The source is simple but accuracy really depends on the quality of the components used. The bridge is more forgiving but you should use 0.1% resistors in close proximity to balance the thermal effect.

The wire gage, its length, and the type of connection used to wire your sensor can have an effect. You are measuring a millivolt level signal. Minimise the voltage drop in the cable and connectors. Gold plating or soldering is almost a must. Use a twisted pair sheilded cable grounded at the amplifier end only.

The amplifier you use and the resistors / capacitors are very important. If your amplifier's gain varies by 1% from cold to warm, forget about 0.1% precision on your measurement.

Make sure that your A/D converter has the resolution and stability to obtain your objective. It is particularly important if your amplifier's output is in the fraction of a volt range.

If your sensor and signal processing system have a repeatable error, make a curve and subtract it from future measurements.

If the equipment is affected by thermal drift, place it in a temperature controlled oven.

Start with this and call me in the morning if it is not better...

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#14

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/11/2012 8:33 AM

To give you an idea of the sort of values you're dealing with, standard pt100 RTDs have a characteristic value change of 0.00385 Ω/Ω/degC.

That translates to about 0.4 Ω/degC in your range, or 0.004 Ω change for a temperature change of 0.01 °C.

With an excitation current of say 10mA, the output voltage would be about 1V, and would change by about 40μV per 0.01 °C.

You would definitely need laboratory grade sensors and measuring equipment, not suitable for an industrial environment or application.

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#16

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/11/2012 9:24 AM

The folks at NIST are the experts on precision temperature measurements. I suggest you contact them. If you can't find the right people to talk to I can get contact information. I suspect one of the first questions they will ask you is whether you actually require .01 deg. accuracy, or if .01 deg. resolution is adequate.

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#19

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/11/2012 9:54 PM

..trying to detect global warming perhaps?

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#20

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/12/2012 2:05 AM

You might read up on the literature of low temperature physics and Bose Condensates where temperatures in the order of mili-Kelvin are measured. Or, call a university near you, and talk to someone in the physics department.

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#21

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/12/2012 2:38 AM

Click on the instrument...

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#24

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/12/2012 3:55 PM

I find that objecting the need for 0.01C accuracy is not the real issue.

To solve this problem, back in the 70's I made a study on temperature measurement accuracy for my Bachelor's degree thesis. I found that the 0.01 C accuracy was required for reaction kinetics studies.

My conclusion was that the best sensor was to use a Thermistor. Although it has a non linear resitance vs temperature characteristic, it can be calibrated versus high accuracy laboratory master thermometers. I agree that the accuracy and stability of the circuit is as important as the sensor accuracy. The coupling of the sensor to the process is of paramount importance. The thermowell may have a greater impact than all the other components and shall be specially designed for this application. The lead wires shall be thick and made of an alloy with very low resistance vs temperature coefficient, such as Constantan.

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#25

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/13/2012 12:48 AM

Thanks for the enlightening comment. What I find intensely curious, the OP's complete disengagement from the discussion.

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#26

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/13/2012 1:51 AM

Normal

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#27

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/13/2012 8:20 AM

You are welcome.

In my 1970's thesis work I found that Thermistors are best for 0.01C accuracy because these devices have the largest change of physical property vs temperature. in this case, ohms/°C.

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#28

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/13/2012 9:42 AM

In the late 70s and 80s precision current sources were developed in an Integrated Circuit form. Feeding a forward biasedsilicon diode by it, the voltage drop on it only depends on bandgap pysics. The voltage is precisely calculable, and - if my memory serves - declines at -26mV/C degree.

So, the OP has now 2 excellent ways to get the repeatibility he desires. I am sure, we could dig up a 3rd one too.

By the way, a fellow brought the picture of an instrument with too many digits. They look sexy, have nothing to do with absolute measurements. In tuning something, they might indicate slight variations, whose absolute value we have not the foggiest notion of.

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#29

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/16/2012 4:03 AM

I thank you all for your responses. They are really very useful for me. although I noticed the lack of a quantitative study that consider the sources of measurement errors for RTDs and shows by following a theoretical ( mathematical and physic ) raisonment how signal conditionning can correct these errors to obtain the desired accuracy. all that I found your answers there included, are, rather general advice. and if you can indicate me a link to a quantitative study on RTDs and how conditionning can improve their performance. It will be really appreciable.Alpha

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#30

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/16/2012 4:52 AM

Sorry to disappoint you.

Did you not find anything enlightening when you Googled RTD signal conditioning?

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#31

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/16/2012 10:26 AM

You got plenty of info in bits and pieces. So I summarize for you. But, plenty of learning is still needed. Otherwise you read some nice marketing piece, and willing to believe it.

1,. Thermocouple.

Advantage:Easy to build. Its output only depends on physics. Very wide temperature range.

Disadvantage: very low output voltage. Easily contaminated by similar voltages from connectors, terminals etc. Very low signal to noise ratio 1:100 or worse.

2,. Thermistor.

Advantage: large signal, a large fraction of a Volt. Can be DC or AC, your choice. Large signal to noise ratio.

Disadvantage: Nonlinear. Needs calibration. For high precision it can get extensive. Using microprocessor the correction table can be included. Limited temperature range.

3,. Diode.

Advantage: large signal, around 0,6V, -26mV/degreeC, dependent only on physics. Linear with a precision current source. Large signal to noise ratio.

Disadvantage: Limited temperature range. 150-200C max., liquid nitrogen temp at the low end, where it run out of useable signal.

4,. There are IC chips, containing the diode, signal conditioning and amplifiers, giving large, well calibrated signals, ready to use. Search for "thermometer integrated circuits". Absolute accuracy may differ, but resolution with 9 - 12 -or better bits is excellent. And that is for inexpensive, under 1\$ chips.

5,. Generally, the signal to noise ratio establishes, how precisely you are able to measure anything. If it is poor, maybe 1 or 2 useful digits come out. Large signals with large stability and low noise may yield 4 or more digits. This is simply a rough guideline. Calibration technicians and the masters of the art can do remarkably more. But, it is not where you are at now.

6,. I tend to distrust published claims for thermocouple signal conditioners. My calculations do not support the claims I read, by a long shot. They may, iust may perform close to spec on repeatability, but not on absolute measurements.

You, the customer have no clue about it, nor any ready way to check it out. But, if you care, plenty to learn.

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#32

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/16/2012 11:30 AM

There is one additional limitation that you did forget in all of these measurement approaches and that is the thermodynamics of the set up and the collection of differential equations that this will entail. All of these probes only report their temperature and not the temperature of the media they reside in. There will always be a small but potentially significant difference between the probe and media to be thermally measured. The tiny mass of a thermocouple will make the time constant of this thermal exchange quicker however it will also make it more prone to self heating. All of these methods will also have the added complication of the wire leads themselves transferring heat into or out of the probe.

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#33

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/16/2012 12:42 PM

Does a thermocouple exhibit self-heating? Just asking.

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#35

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/16/2012 4:03 PM

Depending on how one reads the voltage produced, yes it can self heat. The problem is the bias currents of the sensing circuitry and almost never is a problem until one is working with cryogenics but it does happen.

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#36

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/16/2012 7:51 PM

I guess that could be a problem - but not very significant in [10°C,60°C] .

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#37

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/16/2012 11:25 PM

True but to get four degrees of valid significant figures, one should resolve five degrees of figures. Right now I would not casually dismiss any plausible errors.

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#34

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

08/16/2012 2:41 PM

I'm with John on the thermocouple self-heating.

Some of the smallest thermistors are smaller than any thermocouple I've seen, and their really tiny wires can't conduct much heat in or out. Their self-heating is small and fairly predictable with low sensing current.

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#38

Re: [10°C,60°C] Temperature Measurement with +-0,01°C of accuracy

10/15/2012 8:45 PM

It is possible, but going deeply into details is required. It would take too many pages to write here. Write to me directly.

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