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If I use a .01 cap and this PTC Sensor That start at 50 ohms In this example it — Parallax Forums

If I use a .01 cap and this PTC Sensor That start at 50 ohms In this example it

sam_sam_samsam_sam_sam Posts: 2,286
edited 2008-05-04 21:24 in General Discussion
What size cap do I use for PTC Sensor That start at 50 ohms and gose up in ohms as Temp gose up

The range of the PTC Sensors is unknow at this time· I have to wait until i get them to see what the range is all i know now is that at 77*F it start at 50 ohms

I would like to know.......?


I would like to use this example it shows a .01 Cap and a 10 k ohm rest to use this example



·This the demo code that i want to use
' Applied Sensors - RCTIMEDemo.bs2
' Simple demo of the RCTIME command.
' {$STAMP BS2}
' {$PBASIC 2.5}
rct VAR Word············' Word variable to track time.
n VAR Byte··············' Variable for the bar graph.
LOW 10·················· ' Discharge the capacitor.
DO······················ ' Beginning of the main routine.
RCTIME 10, 0, rct····' Time for the volts to rise to 1.3V.
LOW 10···············' Discharge the capacitor to 0 volts.
DEBUG ? rct·················' Show the time.
n = (rct - 1) / 2048 + 1··' Calculate length of bar graph.
DEBUG REP "*"\n, CR········' Display ASCII art bar graph.
PAUSE 50·················· ' Slows down the program.
LOOP·············' Back to the beginning of main routine.

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··Thanks for any·idea.gif·that you may have and all of your time finding them

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Sam

Post Edited (sam_sam_sam) : 5/4/2008 12:43:32 PM GMT

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2008-05-04 13:15
    What is the highest temperature that you expect and what·do you expect·the resistance be at that point?·

    As temperature increases, resistance increases, and so RCTIME results/counts will increase.

    RCTIME units = 635 x R (in k&#937[noparse];)[/noparse] x C (in µF)

    [color=red]Using 50_ohms and 0.01uF:[/color]
 
[color=red]RCTIME = 635 x 0.05 x 0.01[/color]
[color=red]       = 635 x 0.0005[/color]
[color=red]       = 0.3175[/color]
[color=red]Unacceptable.[/color]
 
 
[color=blue]Using 50_ohms and 1.0uF:[/color]
 
[color=blue]RCTIME = 635 x 0.05 x 1[/color]
[color=blue]       = 635 x 0.05[/color]
[color=blue]       = 31.75[/color]
[color=blue]Passing fair, but barely.[/color]

    Post Edit -- I suggest that a resistor (1K) in series with the PTC would not be inappropriate.··It's important to know the upper limit, that's a design imperative.·




    Post Edited (PJ Allen) : 5/4/2008 1:30:49 PM GMT
  • skylightskylight Posts: 1,915
    edited 2008-05-04 14:39
    some additional info that may be helpful?

    http://www.temperatures.com/thermistors.html
  • sam_sam_samsam_sam_sam Posts: 2,286
    edited 2008-05-04 21:24
    PJ Allen

    What if I put a 10 uf that would give a 317.5 would that be a better value

    RCTIME units = 635 x R (in k&#937[noparse];)[/noparse] x C (in µF)
    ·
    [color=red]Using 50_ohms and 0.01uF:[/color]
 
[color=red]RCTIME = 635 x 0.05 x 0.01[/color]
[color=red]       = 635 x 0.0005[/color]
[color=red]       = 0.3175[/color]
[color=red]Unacceptable.[/color]
 
 
[color=blue]Using 50_ohms and 1.0uF:[/color]
 
[color=blue]RCTIME = 635 x 0.05 x 1[/color]
[color=blue]       = 635 x 0.05[/color]
[color=blue]       = 31.75[/color]
[color=blue]Passing fair, but barely.[/color]



    skylight

    ThanK You for your reply

    I will read what they have at that link·

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    ··Thanks for any·idea.gif·that you may have and all of your time finding them

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    ·
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    ·
    Sam
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