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SHT-71 cable idea and membrane suggestions? — Parallax Forums

SHT-71 cable idea and membrane suggestions?

ArchiverArchiver Posts: 46,084
edited 2003-07-30 21:56 in General Discussion
I have to make a cable for an SHT-71 so I can put the sensor in an air duct.
I was reading the Sensirion datasheet section about cabling and it talked
about running Vcc and Gnd between the data and sck lines. I was picturing 4
conductor twisted pair and thinking that wouldn't really fit the bill.

Then it dawned on me. Telephone handset wire! 4 conductors, wires flat and
straight through the insulation so it meets the wiring arrangement
requirement. The spacing of the wires is almost the same as the SHT-71s legs
too! Think this would work? Typical length about 24 inches.

The datasheet also talks about using a membrane to protect the sensor
elements from contamination. Any idea what material this membrane should be?
Found the examples for mounting materials but nothing about the membrane.

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2003-07-29 15:14
    PM,

    I have used regular braided phone cable about 60' to send the data from a
    SHT** and it worked fine. Note that the power for the SHT was local, but I
    don't see why you couldn't run the power that far too. I ended up using a
    433mHz transmitter instead of wire, but it did work just fine.

    I used some silk screen to protect the sensor. I tried a 1-2 micron filter
    material, but it really slowed down response time.

    Jonathan

    www.madlabs.info

    Original Message
    From: "pm" <pmeloy@s...>
    To: <basicstamps@yahoogroups.com>
    Sent: Monday, July 28, 2003 8:26 PM
    Subject: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?


    > I have to make a cable for an SHT-71 so I can put the sensor in an air
    duct.
    > I was reading the Sensirion datasheet section about cabling and it talked
    > about running Vcc and Gnd between the data and sck lines. I was picturing
    4
    > conductor twisted pair and thinking that wouldn't really fit the bill.
    >
    > Then it dawned on me. Telephone handset wire! 4 conductors, wires flat and
    > straight through the insulation so it meets the wiring arrangement
    > requirement. The spacing of the wires is almost the same as the SHT-71s
    legs
    > too! Think this would work? Typical length about 24 inches.
    >
    > The datasheet also talks about using a membrane to protect the sensor
    > elements from contamination. Any idea what material this membrane should
    be?
    > Found the examples for mounting materials but nothing about the membrane.
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2003-07-29 15:55
    >The datasheet also talks about using a membrane to protect the sensor
    >elements from contamination. Any idea what material this membrane should be?
    >Found the examples for mounting materials but nothing about the membrane.

    One possibility is Goretex. It allows water vapor to pass, but not
    liquid or dust. The Gore company makes vents specifically for
    electronic applications.

    You can find goretex at a backpacking equipment supplier, bonded to a
    nylon carrier. The carrier would slow down the response, though.

    Another possibility is a sintered filter. Mott company has sintered
    materials with a hydrophobic coating. The Microswitch HIH3602
    humidity sensor in a TO5 can includes one of those in the top of the
    can.

    Any of these options slow down the response quite a bit. Once
    condensatin gets inside, it takes forever to evaporate. The goretex
    is probably the best. The Vaisala field humidity probes include a
    very delicate membrane like that.

    -- Tracy
  • ArchiverArchiver Posts: 46,084
    edited 2003-07-29 16:17
    Just jumping in mid-thread, so I'm not sure exactly what you're trying to
    detect. But if it's pressure, how about using a partially inflated balloon
    or condom as a liquid barrier? In the pro-audio business we do this all the
    time to protect a microphone when we want to capture sounds in a drippy
    cave, etc. A microphone is nothing but a pressure transducer (albeit, a
    somewhat expensive one), and we still get frequency response beyond 10 kHz
    with this sort of barrier.

    Mike Sokol
    www.modernrecording.com
    mikes@m...


    Original Message
    From: "Tracy Allen" <tracy@e...>
    To: <basicstamps@yahoogroups.com>
    Sent: Tuesday, July 29, 2003 10:55 AM
    Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?


    > >The datasheet also talks about using a membrane to protect the sensor
    > >elements from contamination. Any idea what material this membrane should
    be?
    > >Found the examples for mounting materials but nothing about the membrane.
    >
    > One possibility is Goretex. It allows water vapor to pass, but not
    > liquid or dust. The Gore company makes vents specifically for
    > electronic applications.
    >
    > You can find goretex at a backpacking equipment supplier, bonded to a
    > nylon carrier. The carrier would slow down the response, though.
    >
    > Another possibility is a sintered filter. Mott company has sintered
    > materials with a hydrophobic coating. The Microswitch HIH3602
    > humidity sensor in a TO5 can includes one of those in the top of the
    > can.
    >
    > Any of these options slow down the response quite a bit. Once
    > condensatin gets inside, it takes forever to evaporate. The goretex
    > is probably the best. The Vaisala field humidity probes include a
    > very delicate membrane like that.
    >
    > -- Tracy
    >
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2003-07-30 03:11
    The SHT-XX sensors are temperature and humidity, not pressure. Pretty snazzy
    little jobbies too! Plug it in, it works! Digital chip, not analog output.
    No ADC to fool with, just a two wire interface (not I2C but pretty easy).

    Ask it what the temp and humidity is - do a bit of math, you're done!

    I made up a prototype on a solderless breadboard and took it to work. Our
    refrigeration guy brought along two sling psycrometers and we tried it in
    various environments - Ice arena (48F 22% RH), Swimming pool (84F, 69%RH)
    Office (72F, 43%RH). Every time the SHT-71 was 0.2F higher and 0.1%RH higher
    than the average of the two sling psychrometers. Might have been a tad
    closer than that but I rounded to one decimal place in software. Even one
    decimal place is really overkill [noparse]:)[/noparse]

    Original Message
    From: "Mike Sokol - ModernRecording" <mikes@m...>
    To: <basicstamps@yahoogroups.com>
    Sent: Tuesday, July 29, 2003 8:17 AM
    Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?


    > Just jumping in mid-thread, so I'm not sure exactly what you're trying to
    > detect. But if it's pressure, how about using a partially inflated balloon
    > or condom as a liquid barrier? In the pro-audio business we do this all
    the
    > time to protect a microphone when we want to capture sounds in a drippy
    > cave, etc. A microphone is nothing but a pressure transducer (albeit, a
    > somewhat expensive one), and we still get frequency response beyond 10 kHz
    > with this sort of barrier.
    >
    > Mike Sokol
    > www.modernrecording.com
    > mikes@m...
    >
    >
    >
    Original Message
    > From: "Tracy Allen" <tracy@e...>
    > To: <basicstamps@yahoogroups.com>
    > Sent: Tuesday, July 29, 2003 10:55 AM
    > Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?
    >
    >
    > > >The datasheet also talks about using a membrane to protect the sensor
    > > >elements from contamination. Any idea what material this membrane
    should
    > be?
    > > >Found the examples for mounting materials but nothing about the
    membrane.
    > >
    > > One possibility is Goretex. It allows water vapor to pass, but not
    > > liquid or dust. The Gore company makes vents specifically for
    > > electronic applications.
    > >
    > > You can find goretex at a backpacking equipment supplier, bonded to a
    > > nylon carrier. The carrier would slow down the response, though.
    > >
    > > Another possibility is a sintered filter. Mott company has sintered
    > > materials with a hydrophobic coating. The Microswitch HIH3602
    > > humidity sensor in a TO5 can includes one of those in the top of the
    > > can.
    > >
    > > Any of these options slow down the response quite a bit. Once
    > > condensatin gets inside, it takes forever to evaporate. The goretex
    > > is probably the best. The Vaisala field humidity probes include a
    > > very delicate membrane like that.
    > >
    > > -- Tracy
    > >
    > >
    > >
    > > To UNSUBSCRIBE, just send mail to:
    > > basicstamps-unsubscribe@yahoogroups.com
    > > from the same email address that you subscribed. Text in the Subject
    and
    > Body of the message will be ignored.
    > >
    > >
    > > Your use of Yahoo! Groups is subject to
    http://docs.yahoo.com/info/terms/
    > >
    > >
    >
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2003-07-30 03:14
    Response time isn't really an issue - taking a sample every 30 minutes. As
    for drying out, I'm putting the internal heater as a menu item so it can be
    turned on to help out if needed.

    I'll check out the gortex idea. Think I know where I can get some pretty
    easily.

    Original Message
    From: "Tracy Allen" <tracy@e...>
    To: <basicstamps@yahoogroups.com>
    Sent: Tuesday, July 29, 2003 7:55 AM
    Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?


    > >The datasheet also talks about using a membrane to protect the sensor
    > >elements from contamination. Any idea what material this membrane should
    be?
    > >Found the examples for mounting materials but nothing about the membrane.
    >
    > One possibility is Goretex. It allows water vapor to pass, but not
    > liquid or dust. The Gore company makes vents specifically for
    > electronic applications.
    >
    > You can find goretex at a backpacking equipment supplier, bonded to a
    > nylon carrier. The carrier would slow down the response, though.
    >
    > Another possibility is a sintered filter. Mott company has sintered
    > materials with a hydrophobic coating. The Microswitch HIH3602
    > humidity sensor in a TO5 can includes one of those in the top of the
    > can.
    >
    > Any of these options slow down the response quite a bit. Once
    > condensatin gets inside, it takes forever to evaporate. The goretex
    > is probably the best. The Vaisala field humidity probes include a
    > very delicate membrane like that.
    >
    > -- Tracy
    >
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2003-07-30 03:16
    Hmmm, braided... If the straight stuff causes any problems I'll switch to
    braided then. 60' is a LOOOOONG way!

    Original Message
    From: "Jonathan Peakall" <jpeakall@m...>
    To: <basicstamps@yahoogroups.com>
    Sent: Tuesday, July 29, 2003 7:14 AM
    Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?


    > PM,
    >
    > I have used regular braided phone cable about 60' to send the data from a
    > SHT** and it worked fine. Note that the power for the SHT was local, but I
    > don't see why you couldn't run the power that far too. I ended up using a
    > 433mHz transmitter instead of wire, but it did work just fine.
    >
    > I used some silk screen to protect the sensor. I tried a 1-2 micron filter
    > material, but it really slowed down response time.
    >
    > Jonathan
    >
    > www.madlabs.info
    >
    >
    Original Message
    > From: "pm" <pmeloy@s...>
    > To: <basicstamps@yahoogroups.com>
    > Sent: Monday, July 28, 2003 8:26 PM
    > Subject: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?
    >
    >
    > > I have to make a cable for an SHT-71 so I can put the sensor in an air
    > duct.
    > > I was reading the Sensirion datasheet section about cabling and it
    talked
    > > about running Vcc and Gnd between the data and sck lines. I was
    picturing
    > 4
    > > conductor twisted pair and thinking that wouldn't really fit the bill.
    > >
    > > Then it dawned on me. Telephone handset wire! 4 conductors, wires flat
    and
    > > straight through the insulation so it meets the wiring arrangement
    > > requirement. The spacing of the wires is almost the same as the SHT-71s
    > legs
    > > too! Think this would work? Typical length about 24 inches.
    > >
    > > The datasheet also talks about using a membrane to protect the sensor
    > > elements from contamination. Any idea what material this membrane should
    > be?
    > > Found the examples for mounting materials but nothing about the
    membrane.
    > >
    > >
    > > To UNSUBSCRIBE, just send mail to:
    > > basicstamps-unsubscribe@yahoogroups.com
    > > from the same email address that you subscribed. Text in the Subject
    and
    > Body of the message will be ignored.
    > >
    > >
    > > Your use of Yahoo! Groups is subject to
    http://docs.yahoo.com/info/terms/
    > >
    > >
    > >
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2003-07-30 15:37
    PM,

    If response time isn't a big deal, the filter material I tried would be
    great. It is easy to use, rigid and tough. I would worry about gortex if
    condensation can build up near the sensor. Once goretex gets wet on the
    inside, it takes forever to dry out. I'm not knocking the stuff, but it
    isn't as great as advertised, in my experience. I own a lot of climbing and
    camping gear with Gortex, and that is just what I have seen.

    I don't know how you plan on mounting the sensor. I put mine in a waterproof
    flashlight, with the sensor where the light bulb usually goes. The filter
    material takes the place of the lens. It's a great and cheap package
    solution for me, and since I made it wireless I can hang it anywhere. This
    unit sat in an exposed location for most of last winter, getting directly
    rained on, and is doing great. I don't think the internal heater will be
    very effective for combating condensation, depending on how large the cavity
    is that houses the SHT. I think it more or less just dries out the sensor.

    Jonathan

    www.madlabs.info

    Original Message
    From: "pm" <pmeloy@s...>
    To: <basicstamps@yahoogroups.com>
    Sent: Tuesday, July 29, 2003 7:14 PM
    Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?


    > Response time isn't really an issue - taking a sample every 30 minutes. As
    > for drying out, I'm putting the internal heater as a menu item so it can
    be
    > turned on to help out if needed.
    >
    > I'll check out the gortex idea. Think I know where I can get some pretty
    > easily.
    >
    >
    Original Message
    > From: "Tracy Allen" <tracy@e...>
    > To: <basicstamps@yahoogroups.com>
    > Sent: Tuesday, July 29, 2003 7:55 AM
    > Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?
    >
    >
    > > >The datasheet also talks about using a membrane to protect the sensor
    > > >elements from contamination. Any idea what material this membrane
    should
    > be?
    > > >Found the examples for mounting materials but nothing about the
    membrane.
    > >
    > > One possibility is Goretex. It allows water vapor to pass, but not
    > > liquid or dust. The Gore company makes vents specifically for
    > > electronic applications.
    > >
    > > You can find goretex at a backpacking equipment supplier, bonded to a
    > > nylon carrier. The carrier would slow down the response, though.
    > >
    > > Another possibility is a sintered filter. Mott company has sintered
    > > materials with a hydrophobic coating. The Microswitch HIH3602
    > > humidity sensor in a TO5 can includes one of those in the top of the
    > > can.
    > >
    > > Any of these options slow down the response quite a bit. Once
    > > condensatin gets inside, it takes forever to evaporate. The goretex
    > > is probably the best. The Vaisala field humidity probes include a
    > > very delicate membrane like that.
    > >
    > > -- Tracy
    > >
    > >
    > >
    > > To UNSUBSCRIBE, just send mail to:
    > > basicstamps-unsubscribe@yahoogroups.com
    > > from the same email address that you subscribed. Text in the Subject
    and
    > Body of the message will be ignored.
    > >
    > >
    > > Your use of Yahoo! Groups is subject to
    http://docs.yahoo.com/info/terms/
    > >
    > >
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and
    Body of the message will be ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    >
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2003-07-30 19:53
    Nice idea, that waterproof flashlight body for mounting the sensor.

    FWIW, it's amazing to me how much mileage the Gore company has gotten
    from its patents on expanded PTFE. Many formulations, many special
    applications. The venting and sensor protection products are
    described at this URL:

    http://www.gore.com/prevent/

    I think the speed of drying on the inside depends a lot on the
    backing material, but I'm really happy with it for outdoor equipment,
    jackets, shoes, hats. I'd rather not be caught on a winter mountain
    trip without it!

    -- Tracy



    >PM,
    >
    >If response time isn't a big deal, the filter material I tried would be
    >great. It is easy to use, rigid and tough. I would worry about gortex if
    >condensation can build up near the sensor. Once goretex gets wet on the
    >inside, it takes forever to dry out. I'm not knocking the stuff, but it
    >isn't as great as advertised, in my experience. I own a lot of climbing and
    >camping gear with Gortex, and that is just what I have seen.
    >
    >I don't know how you plan on mounting the sensor. I put mine in a waterproof
    >flashlight, with the sensor where the light bulb usually goes. The filter
    >material takes the place of the lens. It's a great and cheap package
    >solution for me, and since I made it wireless I can hang it anywhere. This
    >unit sat in an exposed location for most of last winter, getting directly
    >rained on, and is doing great. I don't think the internal heater will be
    >very effective for combating condensation, depending on how large the cavity
    >is that houses the SHT. I think it more or less just dries out the sensor.
    >
    >Jonathan
    >
    >www.madlabs.info
    >
    >
    Original Message
    >From: "pm" <pmeloy@s...>
    >To: <basicstamps@yahoogroups.com>
    >Sent: Tuesday, July 29, 2003 7:14 PM
    >Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?
    >
    >
    >> Response time isn't really an issue - taking a sample every 30 minutes. As
    >> for drying out, I'm putting the internal heater as a menu item so it can
    >be
    >> turned on to help out if needed.
    >>
    >> I'll check out the gortex idea. Think I know where I can get some pretty
    >> easily.
    >>
    >>
    Original Message
    >> From: "Tracy Allen" <tracy@e...>
    >> To: <basicstamps@yahoogroups.com>
    >> Sent: Tuesday, July 29, 2003 7:55 AM
    >> Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?
    >>
    >>
    >> > >The datasheet also talks about using a membrane to protect the sensor
    >> > >elements from contamination. Any idea what material this membrane
    >should
    >> be?
    >> > >Found the examples for mounting materials but nothing about the
    >membrane.
    >> >
    >> > One possibility is Goretex. It allows water vapor to pass, but not
    >> > liquid or dust. The Gore company makes vents specifically for
    >> > electronic applications.
    >> >
    >> > You can find goretex at a backpacking equipment supplier, bonded to a
    >> > nylon carrier. The carrier would slow down the response, though.
    > > >
    > > > Another possibility is a sintered filter. Mott company has sintered
    > > > materials with a hydrophobic coating. The Microswitch HIH3602
    > > > humidity sensor in a TO5 can includes one of those in the top of the
    >> > can.
    >> >
    >> > Any of these options slow down the response quite a bit. Once
    >> > condensatin gets inside, it takes forever to evaporate. The goretex
    >> > is probably the best. The Vaisala field humidity probes include a
    >> > very delicate membrane like that.
    > > >
    > > > -- Tracy
    > > >
    > > >
    > > >
    > > > To UNSUBSCRIBE, just send mail to:
    > > > basicstamps-unsubscribe@yahoogroups.com
    > > > from the same email address that you subscribed. Text in the Subject
    >and
    > > Body of the message will be ignored.
    >> >
    >> >
    >> > Your use of Yahoo! Groups is subject to
    >http://docs.yahoo.com/info/terms/
    >> >
    >> >
    >>
    >>
    >> To UNSUBSCRIBE, just send mail to:
    >> basicstamps-unsubscribe@yahoogroups.com
    >> from the same email address that you subscribed. Text in the Subject and
    >Body of the message will be ignored.
    >>
    >>
    >> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
    > >
    >>
    >>
    >
    >
    >To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    >from the same email address that you subscribed. Text in the
    >Subject and Body of the message will be ignored.
    >
    >
    >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
  • ArchiverArchiver Posts: 46,084
    edited 2003-07-30 21:56
    Tracy,

    Don't get me wrong. I love goretex too, and have a *lot* of equipment with
    it. Even my down sleeping bag has a gortex liner. I igloo camp in the
    winter, and it has become 10X more pleasant since goretex came along. And as
    you pointed out, backing would have a lot to do with it. Most of my stuff is
    heavy duty, so I am sure I have the worst possible backing. But a week of
    winter camping, and goretex is overloaded, everthing is wet, and it can't
    keep up with perspiration. Of course, this is many times the amount of
    moisture that the sensor will ever see.

    Still, I think I like the filter material. It is really strong and easy to
    work with, and will not slow response as much as the goretex. I have a bunch
    of 3" discs of it, if anybody needs some.

    Jonathan

    www.madlabs.info

    Original Message
    From: "Tracy Allen" <tracy@e...>
    To: <basicstamps@yahoogroups.com>
    Sent: Wednesday, July 30, 2003 11:53 AM
    Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?


    > Nice idea, that waterproof flashlight body for mounting the sensor.
    >
    > FWIW, it's amazing to me how much mileage the Gore company has gotten
    > from its patents on expanded PTFE. Many formulations, many special
    > applications. The venting and sensor protection products are
    > described at this URL:
    >
    > http://www.gore.com/prevent/
    >
    > I think the speed of drying on the inside depends a lot on the
    > backing material, but I'm really happy with it for outdoor equipment,
    > jackets, shoes, hats. I'd rather not be caught on a winter mountain
    > trip without it!
    >
    > -- Tracy
    >
    >
    >
    > >PM,
    > >
    > >If response time isn't a big deal, the filter material I tried would be
    > >great. It is easy to use, rigid and tough. I would worry about gortex if
    > >condensation can build up near the sensor. Once goretex gets wet on the
    > >inside, it takes forever to dry out. I'm not knocking the stuff, but it
    > >isn't as great as advertised, in my experience. I own a lot of climbing
    and
    > >camping gear with Gortex, and that is just what I have seen.
    > >
    > >I don't know how you plan on mounting the sensor. I put mine in a
    waterproof
    > >flashlight, with the sensor where the light bulb usually goes. The filter
    > >material takes the place of the lens. It's a great and cheap package
    > >solution for me, and since I made it wireless I can hang it anywhere.
    This
    > >unit sat in an exposed location for most of last winter, getting directly
    > >rained on, and is doing great. I don't think the internal heater will be
    > >very effective for combating condensation, depending on how large the
    cavity
    > >is that houses the SHT. I think it more or less just dries out the
    sensor.
    > >
    > >Jonathan
    > >
    > >www.madlabs.info
    > >
    > >
    Original Message
    > >From: "pm" <pmeloy@s...>
    > >To: <basicstamps@yahoogroups.com>
    > >Sent: Tuesday, July 29, 2003 7:14 PM
    > >Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?
    > >
    > >
    > >> Response time isn't really an issue - taking a sample every 30 minutes.
    As
    > >> for drying out, I'm putting the internal heater as a menu item so it
    can
    > >be
    > >> turned on to help out if needed.
    > >>
    > >> I'll check out the gortex idea. Think I know where I can get some
    pretty
    > >> easily.
    > >>
    > >>
    Original Message
    > >> From: "Tracy Allen" <tracy@e...>
    > >> To: <basicstamps@yahoogroups.com>
    > >> Sent: Tuesday, July 29, 2003 7:55 AM
    > >> Subject: Re: [noparse][[/noparse]basicstamps] SHT-71 cable idea and membrane suggestions?
    > >>
    > >>
    > >> > >The datasheet also talks about using a membrane to protect the
    sensor
    > >> > >elements from contamination. Any idea what material this membrane
    > >should
    > >> be?
    > >> > >Found the examples for mounting materials but nothing about the
    > >membrane.
    > >> >
    > >> > One possibility is Goretex. It allows water vapor to pass, but not
    > >> > liquid or dust. The Gore company makes vents specifically for
    > >> > electronic applications.
    > >> >
    > >> > You can find goretex at a backpacking equipment supplier, bonded to a
    > >> > nylon carrier. The carrier would slow down the response, though.
    > > > >
    > > > > Another possibility is a sintered filter. Mott company has sintered
    > > > > materials with a hydrophobic coating. The Microswitch HIH3602
    > > > > humidity sensor in a TO5 can includes one of those in the top of the
    > >> > can.
    > >> >
    > >> > Any of these options slow down the response quite a bit. Once
    > >> > condensatin gets inside, it takes forever to evaporate. The goretex
    > >> > is probably the best. The Vaisala field humidity probes include a
    > >> > very delicate membrane like that.
    > > > >
    > > > > -- Tracy
    > > > >
    > > > >
    > > > >
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