Stable Temperature Probes
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I am looking to make an inexpensive temperature probe that can be
used with different Basic Stamps without the need to calibrate each
probe with each BS/circuit.
I really need packaging like the AD592 probe that Parallax offers so
the DS1620 is out of the question. Small size is more important then
accuracy and +/- 1 degree would be more then enough. I looked at the
probes that Tracy has, but a cost of $60.00 is prohibitive.
Is there some way to get what I want at a cost that is $10.00 or less?
Hank
used with different Basic Stamps without the need to calibrate each
probe with each BS/circuit.
I really need packaging like the AD592 probe that Parallax offers so
the DS1620 is out of the question. Small size is more important then
accuracy and +/- 1 degree would be more then enough. I looked at the
probes that Tracy has, but a cost of $60.00 is prohibitive.
Is there some way to get what I want at a cost that is $10.00 or less?
Hank
Comments
The LM334DZ, availaable at Digikey is an excellent probe. About 2.30 I
think. Very stable and repeatable. Be sure you use a 1.2K resistor in
series with the sensing lead, and bypass the ADC input with a .1mfd cap.
Sid
Thanks, I'll have to pick up a couple and see how they work.
But that leads me to another question. Won't I have to use a RC
circuit and use RCtime to measure the output? If so, I'm back to the
need to calibrate it with every Stamp circuit it will be used with.
Hank
--- In basicstamps@y..., Newzed@a... wrote:
> For Hank
>
> The LM334DZ, availaable at Digikey is an excellent probe. About
2.30 I
> think. Very stable and repeatable. Be sure you use a 1.2K
resistor in
> series with the sensing lead, and bypass the ADC input with a .1mfd
cap.
>
> Sid
the ADC gives you a digital signal which is equated to temperature./
Sid
I think Sid meant LM34, not LM334. The LM34 has a voltage output of
10mV per degree F that you can feed directly into the ADC. The
LM34DZ is the lowest grade, but it still has an initial accuracy of
+/- 2 degrees F at room temperature, and better than +/- 3 degrees
over the whole range. If you want better accuracy you have to pay
for the "A" grade, which is tested for +/- 1 degree F. I too
recommend those sensors. I have been using them since they first
came on the market.
The LM334, like the AD592, generates a current proportional to
temperature, but to do so it requires one additional "set" resistor.
You do not have to use RCtime to monitor the current. That is how it
was done in "Earth Measurements" because we didn't want to use an
ADC. However, you can pass the current through a precision resistor
and monitor the voltage with an ADC. The LM334 is not very accurate
to begin with, so you would in fact need to do calibration on each
one to achieve anywhere near +/- 1 degree F. Same with the AD592,
you have to pay for the best grade to get the best initial accuracy.
I have DIY instructions for several cable mounted temperature probes
including the LM34, AD592, TMP17, and LM334 on my web site at
http://www.emesystems.com/BS2index.html, and also some BS2
programming and math.
Why do I charge $60 for the temperature probe? It is not just a bare
sensor. The sensor is the "A" grade, and the final step is a
calibration check against a NIST traceable standard, and each sensor
is tagged with its individual calibration constant to bring the the
initial uncertainty to less than 0.2 degree F. It is mounted on a
cable on a special circuit board along with additional components to
isolate it from the cable and to protect it from voltage surges and
wiring errors. And then it is encapsulated and waterproofed, and the
PLTC cable itself is UV and weather resistant. I know it is not a
hobby product. It is directed to biologists who need to measure
temperature reliably in moist field environments. But if you need to
purchase an accurate calibration standard for your own sensors, I
think you will find that it is quite a bargain!
-- best regards
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...
>>>I am looking to make an inexpensive temperature probe that can be
>>>used with different Basic Stamps without the need to calibrate each
>>>probe with each BS/circuit.
>>>
>>>I really need packaging like the AD592 probe that Parallax offers so
>>>the DS1620 is out of the question. Small size is more important then
>>>accuracy and +/- 1 degree would be more then enough. I looked at the
>>>probes that Tracy has, but a cost of $60.00 is prohibitive.
>>>
>>>Is there some way to get what I want at a cost that is $10.00 or less?
>>>
>>>Hank
>>Sid,
>>
>>Thanks, I'll have to pick up a couple and see how they work.
>>
>>But that leads me to another question. Won't I have to use a RC
>>circuit and use RCtime to measure the output? If so, I'm back to the
>>need to calibrate it with every Stamp circuit it will be used with.
>>
>>Hank
>
>--- In basicstamps@y..., Newzed@a... wrote:
> For Hank
>
> The LM334DZ, availaable at Digikey is an excellent probe. About
>2.30 I
> think. Very stable and repeatable. Be sure you use a 1.2K
>resistor in
> series with the sensing lead, and bypass the ADC input with a .1mfd
>cap.
>
> Sid
Doh... OK, now I see. Sorry, didn't catch that at first and now I
understand what you are saying. It's been quite some time since I've
worked on electronics like this, so I need the 'ol brain kick-started
once in awhile!
Hank
--- In basicstamps@y..., Newzed@a... wrote:
> Hank, the output of the LM34 is an analog voltage. Input it to an
ADC and
> the ADC gives you a digital signal which is equated to temperature./
>
> Sid
Thanks for the clarification, I understand better now.
I wasn't dissin' the price on your probes, just using it as an
example as what I didn't need. Heck, for my use, +/- 2 deg. will be
fine, though I'll have to see if the 212 deg. limit is high enough
for my needs. Thanks again for everyone's help, slowly but surely I'm
learning.
Hank
http://www.emesystems.com/BS2index.htm
(not .html) That has DIY instructions for cable mounted temperature probes
including the LM34, AD592, TMP17, and LM334.
Hank, I know you were not dissing the price on the probes. I just
wanted to get a little free advertising! Also I wanted to point out
that it may take several steps to get from the raw sensor to a
practical probe.
Note that Parallax has both the AD592 and the LM34 available on their
web site at
http://www.parallaxinc.com/html_files/component_shop/Sensors.asp
also as part of the Earth Measurements (AD592) or Industrial Control
(LM34) units in Stamps-in-class. For the experimenter the AD592 is
mounted on a cable with waterproofing heat shrink and the LM34 is
mounted on three long wire leads.
-- best regards
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...