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'[PIC] PIC BASED WATER TEMP CONTROLER'
2006\05\17@162442 by VULCAN20

picon face
We are planning a PIC based controller for a solar water collector.  it
will monitor water  temp. at 3 or 4 points and control 2 water pumps for
circulating the water.
We have some NTC 103 thermistors and some solid state relays (3-30V DC
in and 40 to240V AC out.

The sensor may be located as far as 100 FT away. and temprange of  32
deg to200 deg F( approx 0C to 100C)

What I am looking for from the group is this:
Does anyone have Hands on  experience with temperature control sensors
and could recomend a better temperatur sensor.  We would like to imerse
it in the water.

For more details please contact off list.

Thank you.

2006\05\17@165309 by Bob Axtell

face picon face
VULCAN20 wrote:
> We are planning a PIC based controller for a solar water collector.  it
> will monitor water  temp. at 3 or 4 points and control 2 water pumps for
> circulating the water.
> We have some NTC 103 thermistors and some solid state relays (3-30V DC
> in and 40 to240V AC out.
>
> The sensor may be located as far as 100 FT away. and temprange of  32
> deg to200 deg F( approx 0C to 100C)
>
> What I am looking for from the group is this:
>  Does anyone have Hands on  experience with temperature control sensors
> and could recomend a better temperatur sensor.  We would like to imerse
> it in the water.
>
> For more details please contact off list.
>
> Thank you.
>  
I like the National temp sensors with I2C. One/half degree C or better
at a very reasonable price.

What I did was to let the sensors drive an PIC10F200 on a tiny (1/2" x
1/2" sq) PCB. Then obtain the data
then send it serially on one wire (plus pwr/gnd) as slow speed
manchester data. This way prevents any
data loss, even if the distance is extensive (250' +). I have sent
manchester data as far as 500' without
loss, by slowing the bit time to bit-bit interval of 20mS.


2006\05\17@165641 by Bob Axtell

face picon face
VULCAN20 wrote:
> We are planning a PIC based controller for a solar water collector.  it
> will monitor water  temp. at 3 or 4 points and control 2 water pumps for
> circulating the water.
> We have some NTC 103 thermistors and some solid state relays (3-30V DC
> in and 40 to240V AC out.
>
> The sensor may be located as far as 100 FT away. and temprange of  32
> deg to200 deg F( approx 0C to 100C)
>
> What I am looking for from the group is this:
>  Does anyone have Hands on  experience with temperature control sensors
> and could recomend a better temperatur sensor.  We would like to imerse
> it in the water.
>
> For more details please contact off list.
>
> Thank you.
>  
I forgot to mention- to immerse it in water, there are some epoxies that
can contain it waterproof.
I used a two-part epoxy then after that completely dried, I dipped it in
that rubbery "plastigrip"
stuff by Rustoleum. It seals it like a tomb, and can easily handle 100C.

--Bob

2006\05\17@165722 by olin piclist

face picon face
VULCAN20 wrote:
> The sensor may be located as far as 100 FT away. and temprange of  32
> deg to200 deg F( approx 0C to 100C)
>
> What I am looking for from the group is this:
> Does anyone have Hands on  experience with temperature control
> sensors and could recomend a better temperatur sensor.  We would like
> to imerse it in the water.

Whatever sensor you use, I think you should convert to digital close to the
sensor, then send only digital information over the 100ft link.  This can
include checksums so that the receiver knows when something gets corrupted.
Even something like a 10F222 might be good enough, but a little bigger PIC
with 10 bit A/D and UART will be easier.  The current demands should be so
low that you could send 10V or so, linearly regulate that down to 5V at the
sensor, then send back a digital data stream.  If you're worried about
noise, send the data back differentially.  Since temperature changes slowly,
you can use a very slow baud rate and still have it be instantaneous from
the application point of view.  That would require a total of 4 wires:
Power, ground, and 2 differential data lines.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\05\17@170945 by Lindy Mayfield

flavicon
face
Leave it on list this discussion please.  I find it very interesting, especially the sensor part.


{Original Message removed}

2006\05\17@171559 by Harold Hallikainen

face picon face

>  We are planning a PIC based controller for a solar water collector.  it
> will monitor water  temp. at 3 or 4 points and control 2 water pumps for
> circulating the water.
> We have some NTC 103 thermistors and some solid state relays (3-30V DC
> in and 40 to240V AC out.
>
> The sensor may be located as far as 100 FT away. and temprange of  32
> deg to200 deg F( approx 0C to 100C)
>
> What I am looking for from the group is this:
>  Does anyone have Hands on  experience with temperature control sensors
> and could recomend a better temperatur sensor.  We would like to imerse
> it in the water.
>

I did a PIC based veterinary thermometer using a precision thermistor
that's 3k at 25C. I used a 1.3k 0.1% resistor to pull one end up to the
ADC reference voltage, the other end of the thermistor went to ground. I
ran this into a 16 bit ADC (MAX1409). Using a table of resistance values
versus temperature from the thermistor manufacturer, I did a spreadsheet
that yielded the ADC value every 5 degrees C. I put these values in an
array for the PIC to refer to. I did two more arrays, one for the F
degrees for each of those ADC values, another for the C value for each of
those ADC values. The PIC then did linear interpolation to get the value
to display. Use of the ADC reference for the pull-up removed reference
voltage drift from the causes of inaccuracy. Use of a 0.1% pull-up
resistor removed the need for any adjustments in the circuit.

In your application, you may be able to get away with using the 10 bit ADC
on a PIC. Depends on the accuracy you need. I don't think the long wires
to the thermistor will be a problem. I'd run twisted pair and make sure
it's grounded only at the PIC to avoid ground loops. A capacitor across
the ADC input would also remove power line hum (and slow down response,
but temperature changes are slow anyway).

Harold




--
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opportunities available!

2006\05\17@180103 by Spehro Pefhany

picon face
At 03:24 PM 5/17/2006 -0500, you wrote:
>  We are planning a PIC based controller for a solar water collector.  it
>will monitor water  temp. at 3 or 4 points and control 2 water pumps for
>circulating the water.
>We have some NTC 103 thermistors and some solid state relays (3-30V DC
>in and 40 to240V AC out.
>
>The sensor may be located as far as 100 FT away. and temprange of  32
>deg to200 deg F( approx 0C to 100C)
>
>What I am looking for from the group is this:
>  Does anyone have Hands on  experience with temperature control sensors
>and could recomend a better temperatur sensor.  We would like to imerse
>it in the water.

If cost is not that important a factor and assuming you have some analog
design skills, I suggest platinum RTD sensors in a 3-wire configuration.
(leadwire resistance compensated) Assuming this is all outdoors--
being solar and all ;-) be sure to take lighting strikes into account with
wiring placement (inside metal conduit?) and possibly
galvanic isolation of the sensors and sensor wiring. The RTDs are low
impedance, passive, interchangeable without recalibration to a fraction
of a degree  and fairly rugged. They will also be available 10 or 20 years
from now if replacement is required. If you must go high tech, consider a
wireless link.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\05\17@191515 by Jinx

face picon face
> If you must go high tech, consider a wireless link

What I was just thinking. Some very inexpensive 433MHz modules
around. You have power at the sensor end for a digitising PIC and
transmitter

2006\05\29@193708 by Justin Richards

face picon face
Hi vulcan20,

I am curious as what it is exactly you are intending to do.

I guess that you will monitor the temp in the collector, then as this
gets to a certain point you will turn on a pump to circulate the water
(or that coolant type stuff they use for heat exchange glycol) down to
a tank that it located below the collector say in the roof space, or
an outdoor gas heater tank perhaps as opposed to a tank mounted above
the collector that uses convection.

You dont want the water to run continous for two reasons:-

It will draw power continuously  and you see that it may cool down the
water if it is left to circulate thru the collector at night as it
would radiate.

If any of this is anywhere near the mark then perhaps a fan that is
powered from a small solar cell.  As the sun is shinning the water is
circulating.  The panel does not need to be too large as there will be
very little force required for circulation and you only want a trickle
anyway.

Hope this helps.

Regards Justin.

PS Is the vulcan20 related to the vulcan series of water heaters?


On 5/18/06, Jinx <.....joecolquittKILLspamspam@spam@clear.net.nz> wrote:
> > If you must go high tech, consider a wireless link
>
> What I was just thinking. Some very inexpensive 433MHz modules
> around. You have power at the sensor end for a digitising PIC and
> transmitter
>
> -

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