DS1820 temp sensor odd results

[Eric Yancey]

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: http://kitsrus.com/kits.html 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

 

[Jamie]

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: http://kitsrus.com/kits.html 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

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!

 

[Eric Yancey]

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!

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

 

[Graham W]

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.

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

 

[petrus bitbyter]

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: http://kitsrus.com/kits.html 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

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

 

[Uwe Bonnes]

....

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:

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

 

[mike]

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: http://kitsrus.com/kits.html 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

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

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.

 

[Eric Yancey]

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.

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

 

[Homer J Simpson]

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?

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