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William Danielson
 
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Default recmd for low cost, multi point temp logging

Can someone recommend the best, low cost way to monitor temp at 16
pts. We are doing qualifiation tests of an oven used in an bio tech
research application. But we are a startup and I need to stretch my
capital budget as much as possible. Here are the details:

1. type k theromocouople
2. 40-150F temp range
3. 16 tc input channels
4. scan rate = 1 reading / minute
5. log period = 60 hrs

I used National Instruments Field Point modules about 2 yrs ago for
this since they were the cheapest approach I found for the signal
condtioning since a 8 channels of type K tc inputs, the TC120 module,
cost $350.

Is there a better approach I should look at? I do not have to work
with LV or NI hw if there is a better approach.

Thanks in advance for your advice,

Doug Danielson


Atlanta, GA


recmd for low cost, multi point temp logging
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David L Peterson
 
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Default recmd for low cost, multi point temp logging



On 18 Jul 2003 14:59:07 -0700, (William
Danielson) wrote:

Can someone recommend the best, low cost way to monitor temp at 16
pts. We are doing qualifiation tests of an oven used in an bio tech
research application. But we are a startup and I need to stretch my
capital budget as much as possible. Here are the details:

1. type k theromocouople
2. 40-150F temp range
3. 16 tc input channels
4. scan rate = 1 reading / minute
5. log period = 60 hrs

I used National Instruments Field Point modules about 2 yrs ago for
this since they were the cheapest approach I found for the signal
condtioning since a 8 channels of type K tc inputs, the TC120 module,
cost $350.

Is there a better approach I should look at? I do not have to work
with LV or NI hw if there is a better approach.

Thanks in advance for your advice,

Doug Danielson


Atlanta, GA


recmd for low cost, multi point temp logging


I don't remember where I got them from but I had a similar project a
few years ago and found that thermistors are a lot cheaper (and
slightly less accurate) than thermocouples. get an AtoD card for a pc
and you are pretty much in buisness. You'll need some resistors too
for voltage dividers. You need to watch what voltage you put across
them so you don't get significant internal heating. The suppliers
have the schematics and other usefull info. Thermistors don't give
you a linear reaction, so you need to use a table, graph, or an
emperical equation get actual temps. You will also want to calibrate
all of them as there will be some variance between sensors (even if
they were perfect the resistors you use along with them will vary)
rather than try to get them all dead nuts on with little trimpots just
figure a fudge factor for each sensor for when you calculate back the
actual temps. I'd try them all in ice water and boiling water, just
seal them in plastidip or something.before immersing them.

David

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