• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 3 answers
  • Subscribers 30 subscribers
  • Views 407 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

LMT70: LMT70 measure ear drum?

LMT70: LMT70: LMT70 measure ear drum?

Loek Gijben
Prodigy 70 points
Part Number: LMT70
Other Parts Discussed in Thread: TMP117, TMP116

Hi there,

For anyone like me stumbling through the support forms and reading this post:

The original poster says ear *DRUM* measurement. You do not want to have physical contact with an ear drum as an LMT70 requires.

The LMT70 is NOT suitable for ear drum temperature measurements.

Could you please clarify this on that page?

Regards,

Loek Gijben

  • 0
    TI__Guru* 90906 points

    Loek - 

    I think its accepted that tympanic membrane temperature measurement is a good alternative to other traditional ways of measuring body temp and is also called in ear measurement - in this case, of course one would not mechanically contact the membrane, as that could impact hearing, so having two or more high accuracy temperature sensors (like the LMT70 or TMP117 or TMP116) in the ear canal does/can/has been shown to satisfy the application.  

  • 0 in reply to Josh Wyatt
    Prodigy 70 points

    Hi Josh,

    Thank you for the quick answer but it does not satisfy.

    The original answer does not apply to the original question. It should remark that the LMT70 is not suitable for tympanic membrane measurement  (as in ear drum),  but that measuring the ambient and/or skin temperature in the ear canal may be a valid alternative that is readily doable with the LMT70 and other sensors.

    And of course you may point to Infra-red contact-less solutions TI provides for ear drum temperature measurements...  

    IMHO the original answer just adds to confusion.

    Kind regards,

    Loek Gijben

  • 0 in reply to Loek Gijben
    TI__Guru* 90906 points

    Loek - 

    We have done work internally and with customers on this topic and David did state in ear, meaning that. We (TI) do not offer IR temperature measurement solutions. It's obvious you are passionate about the topic and thanks for posting!

  • 0 in reply to Josh Wyatt
    Prodigy 70 points

    Hi Josh,

    I guess we just have to agree to disagree in this topic then.

    I do have  a separate question, please let me know whether I have to start a new topic in this or that you can reply straight away:

    Does the material of the case provide two MOPP to 5V of the internals/pads (according to IEC-60601-1)? I'm aware of not complying with creepage and clearance but in our case we would like to glue the top to a stainless steel pad and  mould-in the (flex)PCB because of the low Junction-to-case (top) thermal resistance.

    Stainless steel to skin, and adhesive between steel and LMT70 as thin as possible. Only doable if the insulation of the case is compliant.

    Regards,
    Loek Gijben

  • 0 in reply to Loek Gijben
    TI__Guru* 90906 points

    Loek - 

    Our temperature sensors are and can be used in medical applications, but we don't classify them as meeting IEC60601 on their own -  and I could not find anything that spoke to lower voltage requirement you mentioned - i think you or your colleagues would more be the experts on this, as the devices your company makes look to be exclusively for medical space. Everything i could find on this so far looked more to be isolation from AC mains to DC domain. 

    WRT the leakage current of the devices - TMP117 has max 0.1uA (I looked up the limit for the MOPP for 60601 standard, i found it to be 50uA for DC supply in normal operation, 100uA for DC supply in fault condition.) LMT70 has max 0.5uA. 

    The LMT70 is a chip scale package, so there is no "case" or insulation to speak of.  

  • 0 in reply to Josh Wyatt
    Prodigy 70 points

    Hi Josh,

    Thanks again for the quick answer.

    Yes we exclusively design and produce medical devices. Temperature sensors are a challenge on its own, especially if one starts to do some calculations on heat flows from skin to sensor to ambient.

    I took a more thorough look at the YFQ0004 drawing at page 12 of the datasheet, i'm sorry I could have done that before asking questions...

    Indeed there is no case but rather one insulation layer on the top side of thickness at least 0.05mm. Is 0.05mm of that material capable of withstanding 1000V for one minute?
    (IEC-60601-1 table 6 first row, test method is described at the beginning of clause 8.8.3 but for our intended use that is not very exciting)
    Does the silicon at the edges have any insulation to the internals, or is it just P or N type base material with maybe a metal oxide layer that is not designed to withstand 1000V?

    Else, can you recommend an insulating material (that provides this 2 MOPP =1000V protection) with a low thermal resistance?

    Kind regards from the Netherlands,

    Loek Gijben

  • 0 in reply to Loek Gijben
    TI__Guru* 90906 points

    Loek - 

    The part is made to withstand ESD strikes, which are measured in nSec time intervals. (+/-2000V for HBM and +/-750V for CDM). We don't test for a duration of time like what you are asking and max voltage and current to any pin otherwise would be as listed in the datasheet (6V and 5mA, respectively)

    Here, since this is a sensor operating at 5V and is not a power supply, wouldn't the isolation be provided at the DC-DC converter side?  I think, if I were you, I would involve your Compliance/Regulatory folks internally to make sure what you are asking about is actually required for this portion of your circuit and its not taken care of upstream already in the design.

    Regarding the the question about the insulation, if its needed - I think you would also need a material that is accepted to touch people as well. I would suggest you reach out to companies like Henkel, Shin-Etsu, Parker, Kyocera and similar to get them to help you find a compound that meets your needs. Sorry to not be more helpful on this topic, but as we don't make that sort of material or test it in the manner you suggest, it would be hard for us to recommend something definitively.  

  • 0 in reply to Josh Wyatt
    Prodigy 70 points

    Hi Josh,

    We are now planning to use a small thin stainless steel curved disk slash bowl to put (a flexPCB with) the LMT70 in, with the top side attached to the disk/bowl for its low thermal resistance. Then potting the whole thing with epoxy or overmould the thing leaving the outside of the disk free.
    So the insulation would be needed between component and steel. The steel touches the skin.
    It will be our challenge to keep the form factor and thus the heat capacity as small as possible. The small size of the LNT70 certainly helps.

    If we take the bowl and put a 0.1mm thick polyimide sticker to the bottom and then attach the LMT70 we would be set, but I was hoping to patch the LMT70 directly to the steel to keep the thermal resistance as low as possible.

    The 60601 suite of standards is complicated and defies logic at many points, which makes it a challenge to go to a test house: one never knows how the local test engineer interprets the standards and how lenient he or she is. The requirements on insulation providing two means of patient protection for 5V DC (actually 17V or less) is straight forward: it must withstand 1000V for a minute, plus ramp up and down. I know, this does not make much sense...

    Thanks for you support to date, although not with the optimal outcome i will flag this issue as resolved :-)

    Kind regards from the Netherlands,

    Loek Gijben