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Re: temperature sensor question

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  • johansea
    Gday Pete The sensor doesnt have to be on the corrector itself, it can be on the outside of the corrector ring, as long as external insulation is used. I have
    Message 1 of 16 , Mar 1, 2004
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      Gday Pete
      The sensor doesnt have to be on the corrector itself, it can be on
      the outside of the corrector ring, as long as external insulation is
      used. I have made ( and am still testing ) a two channel dewbuster
      style heater controller where i have digital sensors on the OTA ring
      ( under foam insulation ) and a seperate one for air. I am
      controlling these with a small microcontroller, so i can set what
      temp delta i want, and also what temp to start the heater running
      at. If you know the dewpoint, you can set the heater to only start
      when OTA temp drops below that plus say 3deg, then hold the OTA a
      set temp above ambient. It was by comparing my OTA temps from this
      testing to the Austostar that i found them to vary considerably.
      Andrew Johansen Melbourne Australia

      --- In LX200GPS@yahoogroups.com, "plalbrecht" <plalbrecht@a...>
      wrote:
      > --- In LX200GPS@yahoogroups.com, Charles Bell
      <quantumhyperspace@y...>
      > wrote:
      > > If you know the dew point for the your current
      > > weather, you can tell if you are close enough to need
      > > to put on your dew shield or dew heater.
      >
      > That is not a useful indicator. Dew will form on the corrector
      while
      > ambient air is still WELL ABOVE the dewpoint temperature.
      >
      > Reason: the glass of the corrector "sees" night sky, and
      effectively
      > radiates to that. Night sky is "cold." Heat transfer through
      > conduction or convection with the surrounding air is not as
      > significant a factor as radiation to the cold night sky.
      >
      > Now, if there were a sensor for the temperature of the corrector,
      > especially the front surface, that would be a different story.
      >
      > A good writeup of the physics involved:
      > http://www.wwnorton.com/astro21/sandt/dew.html
      >
      > Pete
    • plalbrecht
      Right. But the temp sensor (inside the fork arm?) of the LX200 isn t much help in that case. Might as well phone the local weather bureau for similar
      Message 2 of 16 , Mar 1, 2004
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        Right. But the temp sensor (inside the fork arm?) of the LX200 isn't
        much help in that case. Might as well phone the local weather bureau
        for similar information to what the scope delivers. Your method is
        much more effective.

        Pete

        > The sensor doesnt have to be on the corrector itself, it can be on
        > the outside of the corrector ring, as long as external insulation is
        > used. I have made ( and am still testing ) a two channel dewbuster
        > style heater controller where i have digital sensors on the OTA ring
        > ( under foam insulation ) and a seperate one for air. I am
        > controlling these with a small microcontroller, so i can set what
        > temp delta i want, and also what temp to start the heater running
        > at.

        > If you know the dewpoint, you can set the heater to only start
        > when OTA temp drops below that plus say 3deg, then hold the OTA a
        > set temp above ambient. It was by comparing my OTA temps from this
        > testing to the Austostar that i found them to vary considerably.
      • ojfisher
        -If you have a vehicle outside a car or truck just go and rub your hand on the engine hood (engine should be cold)-if there is moisture on your hand you need a
        Message 3 of 16 , Mar 1, 2004
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          -If you have a vehicle outside a car or truck just go and rub your
          hand on the engine hood (engine should be cold)-if there is moisture
          on your hand you need a dew shield o.J. Fisher- In
          LX200GPS@yahoogroups.com, "plalbrecht" <plalbrecht@a...> wrote:
          > --- In LX200GPS@yahoogroups.com, Charles Bell
          <quantumhyperspace@y...>
          > wrote:
          > > If you know the dew point for the your current
          > > weather, you can tell if you are close enough to need
          > > to put on your dew shield or dew heater.
          >
          > That is not a useful indicator. Dew will form on the corrector
          while
          > ambient air is still WELL ABOVE the dewpoint temperature.
          >
          > Reason: the glass of the corrector "sees" night sky, and
          effectively
          > radiates to that. Night sky is "cold." Heat transfer through
          > conduction or convection with the surrounding air is not as
          > significant a factor as radiation to the cold night sky.
          >
          > Now, if there were a sensor for the temperature of the corrector,
          > especially the front surface, that would be a different story.
          >
          > A good writeup of the physics involved:
          > http://www.wwnorton.com/astro21/sandt/dew.html
          >
          > Pete
        • johansea
          Gday Pete ... Agree fully. It makes a nice trend plot over time, but isnt usefull in any way for controlling heaters etc. Thats why i have gone for my own
          Message 4 of 16 , Mar 1, 2004
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            Gday Pete

            --- In LX200GPS@yahoogroups.com, "plalbrecht" <plalbrecht@a...>
            wrote:
            > Right. But the temp sensor (inside the fork arm?) of the LX200
            > isn't much help in that case.

            Agree fully. It makes a nice trend plot over time, but isnt usefull
            in any way for controlling heaters etc. Thats why i have gone for my
            own units. ( Now i've just found a good microprocessor readable
            relative humidity sensor for about $50. Time for more add on extras
            methinks. )
            Andrew Johansen Melbourne Australia


            > Might as well phone the local weather bureau
            > for similar information to what the scope delivers. Your method is
            > much more effective.
            >
            > Pete
            >
            > > The sensor doesnt have to be on the corrector itself, it can be
            on
            > > the outside of the corrector ring, as long as external
            insulation is
            > > used. I have made ( and am still testing ) a two channel
            dewbuster
            > > style heater controller where i have digital sensors on the OTA
            ring
            > > ( under foam insulation ) and a seperate one for air. I am
            > > controlling these with a small microcontroller, so i can set
            what
            > > temp delta i want, and also what temp to start the heater
            running
            > > at.
            >
            > > If you know the dewpoint, you can set the heater to only start
            > > when OTA temp drops below that plus say 3deg, then hold the OTA
            a
            > > set temp above ambient. It was by comparing my OTA temps from
            this
            > > testing to the Austostar that i found them to vary considerably.
          • plalbrecht
            ... Now that you mention it, I have one of these used in another line of work (getting temp and density altitude when road testing cars):
            Message 5 of 16 , Mar 2, 2004
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              > Now i've just found a good microprocessor readable
              > relative humidity sensor for about $50. Time for more add on extras
              > methinks.

              Now that you mention it, I have one of these used in another line of
              work (getting temp and density altitude when road testing cars):

              http://www.kestrelmeters.com/kestrel-4000.htm?source=g-[kestrel_4000]&engine=adwords!346&keyword=kestrel+4000

              I wonder if one of those noncontact infrared "gun" type temperature
              probes would work when pointed at a corrector plate, or would it "see"
              right through it. Don't have one or I would try it.

              Pete
            • johansea
              Gday Pete Nice gizmo. I was thinking more restrained though. Ref http://content.honeywell.com/sensing/prodinfo/humiditymoisture/009012 _2.pdf This is a three
              Message 6 of 16 , Mar 2, 2004
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                Gday Pete
                Nice gizmo.
                I was thinking more restrained though.
                Ref
                http://content.honeywell.com/sensing/prodinfo/humiditymoisture/009012
                _2.pdf
                This is a three pin chip that only requires a regulated power
                supply. The third pin puts out a voltage directly relative to
                humidity. Ideal to build into the controller i am making.
                As to the temp gun, this idea came up a year or so ago ( Thad i
                think ). We were discussing the effect of heater position on OTA vs
                heat transfer through the corrector, to see which method gave the
                most even heating. There was a very nice gun mentioned but it was US
                2-3K so i guess no one bothered. Be nice to check though
                Andrew Johansen Melbourne Australia

                --- In LX200GPS@yahoogroups.com, "plalbrecht" <plalbrecht@a...>
                wrote:
                > > Now i've just found a good microprocessor readable
                > > relative humidity sensor for about $50. Time for more add on
                extras
                > > methinks.
                >
                > Now that you mention it, I have one of these used in another line
                of
                > work (getting temp and density altitude when road testing cars):
                >
                > http://www.kestrelmeters.com/kestrel-4000.htm?source=g-
                [kestrel_4000]&engine=adwords!346&keyword=kestrel+4000
                >
                > I wonder if one of those noncontact infrared "gun" type temperature
                > probes would work when pointed at a corrector plate, or would
                it "see"
                > right through it. Don't have one or I would try it.
                >
                > Pete
              • plalbrecht
                ... It s free... ... 2-3K so i guess no one bothered. The ones I am thinking of are cheap, sold to use on tires and the like. Won t give an IR image, like I
                Message 7 of 16 , Mar 2, 2004
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                • johansea
                  Gday Pete ... wrote: ... Its US280 plus Free shipping for peasants like me. Too much. ... I wasnt considering the gun, it came up in discussions a while ago.
                  Message 8 of 16 , Mar 2, 2004
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                    Gday Pete

                    --- In LX200GPS@yahoogroups.com, "plalbrecht" <plalbrecht@a...>
                    wrote:
                    ......
                    > It's free...

                    Its US280 plus "Free shipping" for peasants like me. Too much.

                    > The ones I am thinking of are cheap, sold to use on tires and the
                    > like. Won't give an IR image, like I suspect the ones you were
                    > considering.

                    I wasnt considering the gun, it came up in discussions a while ago.
                    I see Thad has replied re this also. I knew it was expensive.

                    Andrew Johansen Melbourne Australia
                  • johansea
                    Gday Thad ... I had found these also but no supplier in OZ. I can get the honeywell ones locally so will probably try them out. PS did you see how small the
                    Message 9 of 16 , Mar 2, 2004
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                      Gday Thad

                      --- In LX200GPS@yahoogroups.com, "Thad Floryan" <thad@t...> wrote:
                      .....
                      > Found some neat sensors (and kits) with a simple serial interface
                      > and about the size of a matchhead:
                      >
                      > <http://www.sensirion.com/>

                      I had found these also but no supplier in OZ. I can get the
                      honeywell ones locally so will probably try them out.
                      PS did you see how small the mini sensirion one is. I couldnt even
                      see the pins, let alone solder them :-)

                      Andrew Johansen Melbourne Australia

                      > And don't ask the price (even for rental).
                      How much?
                    • Dennis Friedman
                      Andrew, Thad: I recently used the SHT11-x by Sensitron for controlling my son s Tortoise environment. I used a Basic Stamp though a plain pic processor would
                      Message 10 of 16 , Mar 2, 2004
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                        Andrew, Thad:

                        I recently used the SHT11-x by Sensitron for controlling my son's
                        Tortoise environment. I used a Basic Stamp though a plain pic
                        processor would also have worked. It is easy to work with and gives
                        reasonably accurate results for temp and humidity. If you would like
                        to know more about how I used it check out the webpage on it.

                        www.datainc.com/kardboard.htm

                        You might also want to take a look at my astronomy webpages as well.
                        www.datainc.com/astronomy.htm

                        Regards,

                        Dennis Friedman
                        The "Other" Moderator of TheForce and Hocus Focus Forum

                        --- In LX200GPS@yahoogroups.com, "johansea" <johansea@o...> wrote:
                        > Gday Thad
                        >
                        > --- In LX200GPS@yahoogroups.com, "Thad Floryan" <thad@t...> wrote:
                        > .....
                        > > Found some neat sensors (and kits) with a simple serial interface
                        > > and about the size of a matchhead:
                        > >
                        > > <http://www.sensirion.com/>
                        >
                        > I had found these also but no supplier in OZ. I can get the
                        > honeywell ones locally so will probably try them out.
                        > PS did you see how small the mini sensirion one is. I couldnt even
                        > see the pins, let alone solder them :-)
                        >
                        > Andrew Johansen Melbourne Australia
                        >
                        > > And don't ask the price (even for rental).
                        > How much?
                      • plalbrecht
                        ... Well, you have to have these things when you re a king. ... Pete
                        Message 11 of 16 , Mar 3, 2004
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                          --- In LX200GPS@yahoogroups.com, "johansea" <johansea@o...> wrote:
                          > Gday Pete
                          >
                          > --- In LX200GPS@yahoogroups.com, "plalbrecht" <plalbrecht@a...>
                          > wrote:
                          > ......
                          > > It's free...
                          >
                          > Its US280 plus "Free shipping" for peasants like me. Too much.

                          "Well, you have to have these things when you're a king."

                          :-)

                          Pete
                        • johansea
                          Gday Thad ... attractive ... Thats exactly the use i am working on now. Just had a look at Dennis Friedmans turtle heater. Nice use also. My new controller
                          Message 12 of 16 , Mar 3, 2004
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                            Gday Thad
                            --- In LX200GPS@yahoogroups.com, "Thad Floryan" <thad@t...> wrote:

                            > Didn't see those (no pun :-), but the small size makes it
                            attractive
                            > for scope use in a 3rd generation dew strip controller by actually
                            > calculating the dew point via a small microprocessor or PIC.

                            Thats exactly the use i am working on now.
                            Just had a look at Dennis Friedmans turtle heater. Nice use also.
                            My new controller uses DS18B20 sensors for temp control. I am using
                            a Pic16F876 as i get two hardware generated PWM channels, so i can
                            run two independently controlled heaters in background mode. I can
                            also set all my variables using buttons and an LCD, so its easy to
                            see/set variables. All that currently runs sweet on a breadboard and
                            i have almost put a prototype box together. Now all i need is
                            humidity and i can calc dewpoint.
                            I now need to go back to my numerical techniques book to figure out
                            how to incorporate the math reqd in a PIC. My head hurts

                            > I need to locate a supplier of the Sensirion parts

                            Can help there now. Whilst no distributors show up for OZ
                            FarnellInOne stock them.
                            SHT11 is sn 3913065 or better still SHT71 with sn 4130686.
                            The latter is just a SHT11 with a 4pin SIP connector prefitted. Much
                            safer for me than soldering.

                            Andrew Johansen Melbourne Australia
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