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'[EE]: Temperature Sensors?'
2002\12\01@005646 by Jinx

face picon face
> What temperature sensors would you recommend for:
>
> -Fast Response Time (90% of actual temp)
> -Relatively Cheap (This is a school project, so nothing that costs
> $100)
> -EASY to program for using PIC16F877 - This is a must! Themistors
> are looking to be very difficult to program for, for a nice accuracy
> -Accuracy of sub +- 1degreeC
>
> I've also messed around with thermistors, just printing out an ADC
> value and they seem to vary the most, but they are hard to program
> for as they are non-linear, and they change over age

Use a look-up table to avoid calculations. You'll need to do at least
one very careful set of measurements to make the table

> Are there any other solutions i haven't thought of? What are your
> opinions of solution i need?

Use the PIC's WDT. Its period changes with temperature and is
pretty linear. You can improve the response time of a sensor by
fixing it to a heatsink - they work both ways. What response time
are you after ?

"EASY to program" is very subjective. Unless you find a sensor
that tells you what it knows the way you want it by 8-bit parallel
data, you'll have to do some calcs

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2002\12\01@012736 by Peter McNulty

picon face
Hi,

Response time for 90% of actual  temperature, i'd like under a minute at
least. I'm fine with doing some simple calculations, but i wouldn't like to
use a lookup table, as if the thermistor would ever need to be replaced, the
table would have to be changed, the measurements taken again, etc. By easy
to program, i mean, a few multiplications/divides/subtracts are okay, but i
don't what any like ln, or sine functions or anything like that.

I'm ok paying up to about $10 roughly for the sensor, but i'm finding the
LM335 and maxim/dallas chips have a very very slow response time, up to
about 3 minutes or more, which isn't what i need. Now thinking about it, an
accuracy or 1 degree is perfectly fine, and with some calibration i  could
probably make it even closer.

I can't use the PICs WDT as i need a small sensor that can fit into small
areas, via a couple of wires.

-Peter
{Original Message removed}

2002\12\01@020132 by Jinx

face picon face
> I'm ok paying up to about $10 roughly for the sensor, but i'm
> finding the LM335 and maxim/dallas chips have a very very
> slow response time, up to about 3 minutes or more, which
> isn't what i need. Now thinking about it, an accuracy or 1
>degree is perfectly fine, and with some calibration i  could
> probably make it even closer.

This small pdf shows what can be done with thermistors

http://www.metone.com/pdf/060seriesDS.pdf

They claim < 10 seconds response time and 0.1C with something
called a "multi-stage solid state thermistor, highly linearised"

Google for +thermistor +"response time"

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2002\12\01@140553 by Herbert Graf

flavicon
face
> Hi,
>
> Response time for 90% of actual  temperature, i'd like under a minute at
> least. I'm fine with doing some simple calculations, but i
> wouldn't like to
> use a lookup table, as if the thermistor would ever need to be
> replaced, the
> table would have to be changed, the measurements taken again, etc. By easy
> to program, i mean, a few multiplications/divides/subtracts are
> okay, but i
> don't what any like ln, or sine functions or anything like that.
>
> I'm ok paying up to about $10 roughly for the sensor, but i'm finding the
> LM335 and maxim/dallas chips have a very very slow response time, up to
> about 3 minutes or more, which isn't what i need. Now thinking
> about it, an
> accuracy or 1 degree is perfectly fine, and with some calibration i  could
> probably make it even closer.

       Have you looked at the LM75, I don't know what it's response is like but
I've seen it change very quickly, relativly. TTYL

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