DS1820 temp sensor odd results

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Eric Yancey 19 years ago

Hello,

I recently installed a temperature monitoring system for my home workshop. The primary goal is to monitor the heat capacity and dissipation of a concrete slab floor with radiant heat tubing. When I installed the heating tubes before the concrete was poured, I embedded a fairly short (5 feet or so) piece of PEX tubing to house a temperature sensor.

I built kit 145 from here:

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to interface with four dallas DS18S20 sensors. One sensor measures ambient air temp, two measure the temperature of the fluid entering and exiting the floor, and the fourth is inserted in the terminated PEX tube as described above.

The problem I'm having is that the 4th sensor is reporting flaky results. I replaced the original sensor but the replacement is exhibiting the same behavior as the original. Here is some sample data:

07:45:00 78.35
07:44:30 74.07
07:44:00 71.15
07:43:30 72.50
07:43:00 75.20
07:42:30 67.42
07:42:00 74.62
07:41:30 67.32
07:41:00 75.97
07:40:30 71.15
07:40:00 73.96
07:39:30 69.80
07:39:00 69.80
07:38:30 78.01
07:38:00 73.96
07:37:30 57.87
07:37:00 70.57

02:01:00 61.25

02:00:30 86.11
02:00:00 84.76
01:59:30 59.56

Around midnight the sensor was reporting temperatures consistently around

60F which I believe is the actual temperature of the slab. From around
2:00AM this morning it started reporting inconsistent values, and now, around 8:00AM, it is reporting temperatures anywhere from 57F to 78F, which I know is not correct (the temp of a concrete slab cannot fluctuate 30 degrees in 8 minutes).

Does anyone have any ideas on why this may be happening?

I apologize for the length of the message and thanks for any help!

Eric Yancey

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Jamie 19 years ago

lost soles of those lying in the cement below that slab? :)

Radon gas?, some element mix in the concrete that maybe reacting to a near by R.F. signal at times? who knows! :)

"I am never wrong, once i thought i was, but i was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5

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Eric Yancey 19 years ago

Haha, well, it was built on an ancient indian burial ground :)

The RF signal is an interesting idea, but 3 of the other sensors are within

3' of the flaky one, so who knows?

I'm gonna pull the sensor this evening and see if I get accurate readings outside of the slab.

Eric

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Graham W 19 years ago

Then swap it with another one you assess as working properly?

-- Graham W

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PGM-FI page updated, Graphics Tutorial WIMBORNE

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Wessex Astro Society's Website Dorset UK Info, Meeting Dates, Sites & Maps Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

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petrus bitbyter 19 years ago

"Eric Yancey" schreef in bericht news:ZtednVgxpfMvkKPYnZ2dnUVZ snipped-for-privacy@giganews.com...

Some thoughts.

Did you try to change the connection so to eliminate a faulty chip or a bad connection? Same for the sensors.

Radiation (electromagnetic radiation) of any source can disturb the signal from the sensor. Twist the wires carfully or try a piece of shielded cable and ground the shield.

The sensor may not make a good thermal contact with the concrete, so your results may reflect the temperature of the air in the tube instead of the concrete around. You can try to close the tube using a cork or fill the tube with fine dry sand (as for birds cages so you can remove it using a vacuum cleaner).

petrus bitbyter

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Uwe Bonnes 19 years ago

...

Read 9 Bytes after the CONVERT_T command and the conversion complition. That way you get the CRC8 and you can check the data for integrity.

Discard and reread if CRC8 fails.

Bye

Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt --------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

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mike 19 years ago

If your test of the sensor outside the slab shows as I suspect that it is OK, I think your issue may be due to temperature fluctuations in the still curing concrete. IIRC, concrete, when it is curing generates heat. This heat will gradually fall off towards the ambiant temperature in time, but as you said that the slab was recently laid, maybe that has not had time to complete in the center. You could double check by drilling a hole (remember where the pipes are?) and inserting a mercury thermometer to see if the same thing happens. As the fluid is in motion it will not exhibit the swings as not enough time will have occured between entry and exit for transfer. As it is a heating system, I guess the liquid's temperature will be higher than that of the slab anyway, so heat transfer will be away from the liquid.

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Eric Yancey 19 years ago

workshop.

heating

or

with

the

results. I

heat.

Thanks Mike and everyone else for your replies and suggestions. I should have been a bit more clear - the concrete was installed about a year ago so it should be mostly cured by now. Yesterday I pulled the sensor from the PEX, taped it to the floor, and placed a metal clamp on top of it. Since then the temps have been pretty consistent, varying only by half a degree or so between samples over the last 24 hours.

I'm considering wrapping some sort of insulating material around the sensor and then putting it back in the floor. Not sure what else to try at this point?

Thanks again,

Eric

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Homer J Simpson 19 years ago

Can you replace the sensor with a short or a resistor and see what happens?

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DS1820 temp sensor odd results

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