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Old 01-26-2010, 04:33 AM   #1
Yuri_Rage
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Default An interesting thermocouple/filtering phenomenon

If you want to get the gist of my post without reading all of the detail, just read the bold text.

In the interest of fast response time, I ordered grounded thermocouples for my electric brew rig. However, I failed to realize that grounded thermocouples are even more susceptible to noise than the non-grounded variety. I really should have done another 5 minutes worth of homework before ordering some rather expensive sensor packages. As a result,

I get very jittery output with occasional extreme spikes.

After doing most of the soldering/wiring on my new Arduino shield,

I decided to run the thermocouple outputs through a software filter adapted from the one on this webpage.

It works very well. The sensor output jitter is now reduced to about 0.5. The filter uses 12 samples at a rate of 2 Hz, effectively resulting in a 6 second response time. But that's not the interesting part.

*** Filtering the output actually resulted in a bit of unanticipated calibration in both accuracy and precision. ***

Of the two thermocouples that I have connected,

one of them always seemed to read a degree or two low, and the other was always a few degrees high.

The smoothed output now shows the sensors steady within 1 of one another at +/- 1 of the actual process temperature.


I'm quite amazed at this simple brute force filtering technique!


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Old 01-26-2010, 04:43 AM   #2
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Would be nice to see some graphs (formal or not!) of the readings before and after the filtering.


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Old 01-26-2010, 04:45 AM   #3
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Here is some empirical data: http://twitter.com/kampferstrahl.

The sensors are within a few feet of one another and have been registering ambient temperature in the brew hut for days. All of the readings before 30 minutes ago (25 Jan 10, 10:15 PM, CST) were before I applied any filtering.

I also did a little testing with some icewater, and the results were similar. I don't feel particularly inclined to graph the results, as the observed output is quite adequate.
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Old 01-27-2010, 10:29 PM   #4
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Not sure about your setup, but would ferrite beads on the grounding wire reduce some of the noise?
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