Measuring Human body temperature accurately - Page 1
Forum section: electronics / projects

author: tyguy2
author_rank: Unknown
timestamp: May 21, 2016, 05:23:03 pm
content: I'm trying to find a sensor that can measure body temperature accurately (at least +- 0.5 C). I was thinking I would usehttp://www.analog.com/media/en/technical-documentation/data-sheets/ADT7420.pdfbut I don't think that would work if I wanted to measure the internal body temp of a person.https://www.sparkfun.com/products/9570This is way to expensive (I'm trying to put this on a PCB I'm creating, and $20 is way too much per board). Does anyone have any ideas?

author: danadak
author_rank: Super Contributor
timestamp: May 21, 2016, 06:36:53 pm
content: Melexis sells IR temp sensors. Calibrated, and by selecting a small beamangle, you should be able to take accurate T of a persons throat, whichshould give you internal T. All done non contact.http://www.melexis.com/Products-By-Category/Infrared-Thermometer-Sensors-155.aspxRegards, Dana.

author: tyguy2
author_rank: Unknown
timestamp: May 21, 2016, 08:11:30 pm
content: Would this work if it was pressed to someone's skin?

author: m98
author_rank: Frequent Contributor
timestamp: May 21, 2016, 08:53:01 pm
content: If pressed to the skin, you wouldn't need to use an infrared sensor. Where do you want to put the sensor?

author: IanB
author_rank: Super Contributor
timestamp: May 21, 2016, 09:06:51 pm
content: Quote from: tyguy2 on May 21, 2016, 05:23:03 pmFirstly, ±0.5°C is not accurate for body temperature. You would need more like ±0.1°C for that. Secondly, human body temperature is not the same everywhere, especially around the periphery. So the expected temperature depends on where you measure it.What are you trying to achieve and why?

author: Marco
author_rank: Super Contributor
timestamp: May 21, 2016, 09:08:10 pm
content: Temporal artery thermometers can do it, but I don't quite understand how they work. The ones you have to track across your forehead are easy enough to understand, they just determine a max of the curve to get the temperature value at the artery. There are also ones you simply point and click, I guess they could be using a linear array, but they are pretty cheap. I'd buy one of the latter and tear it down to see how it works.

author: tyguy2
author_rank: Unknown
timestamp: May 21, 2016, 09:15:42 pm
content: I'm trying to measure internal body temp by placing a sensor on the finger, arm, wrist. Isn't the surface of the skin slightly colder than internal body temp? The IR light can penetrate the surface and get a more accurate reading, correct? I agree, +- 0.1 C is probably better. The sensor needs to sense a person's body temp via the surface of the skin, even if they are sweating. That's why I would think IR would be better, but I'm probably wrong. The sensor has to be digital, because I don't have any available ADC's on my micro controller.

author: uncle_bob
author_rank: Unknown
timestamp: May 21, 2016, 09:25:57 pm
content: Quote from: tyguy2 on May 21, 2016, 09:15:42 pmHiAn arbitrary point on the finger / arm / wrist can be *much* cooler than the internal body temperature. That's true if you do it by contact or by IR or by a trained flea with a Fluke meterTo be useful for any sort of diagnostic test, you will indeed need something in the 0.1C or below range. A number that is off by one or two C (as a point on the skin can *easily* be) does not do much good. A person with circulation issues in a cool room can go way past a couple degrees C for finger temperatures ...Bob

author: tyguy2
author_rank: Unknown
timestamp: May 22, 2016, 02:40:39 am
content: Where would you suggest I take reading? I can't put it in the mouth.

author: Marco
author_rank: Super Contributor
timestamp: May 22, 2016, 02:44:37 am
content: Forehead, but you want to put it right on the artery ... which is invisible.

author: uncle_bob
author_rank: Unknown
timestamp: May 22, 2016, 02:48:20 am
content: Quote from: tyguy2 on May 22, 2016, 02:40:39 amHiThe gotcha is that this is (as they say) "a well studied field". There are a few well known solutions and a bunch of poor answers. The well known solutions are backed up by good stuff like clinical trials and have offset numbers so they can be used in the real world. Even if you have a "magic location" if it is different than the prior art, you need to do all of the trials.So: How much do you have budgeted for clinical trials?I'd bet the answer is ... zip. So back to the well known approaches. Thermometer goes here / thermometer goes there / thermometer is implanted here / IR scan to find blood vessel this way. Anything else will simply give you relative data. If this is a diagnostic application ... not much use. If it's for something else, then you might want to spell out just what that something else is.Bob

author: tyguy2
author_rank: Unknown
timestamp: May 22, 2016, 03:18:31 am
content: It's a sensor is going to be attached to a person while running or performing labor intensive tasks. So what you're saying is that it's kind of impossible to find the "best" kind of sensor? What would be the "best," relatively speaking? IR? IC's dedicated to temp sensing?

author: VK5RC
author_rank: Unknown
timestamp: May 22, 2016, 03:25:22 am
content: The places that are thought to be really reliable for core body temperatures are internal eg high rectal or oesophageal, hypothermic victims have a probe placed (would be unpleasant - but these guys aren't conscious) quite early on in the resuscitation.As Bob says, the standard locations eg sub-lingual location is socially acceptable and accessible, but there are issues of hygiene etc.The tympanic membrane (the internal end of the ear canal) is good but cannot be touched without risk of rupture, hence IR reading technique used.

author: IanB
author_rank: Super Contributor
timestamp: May 22, 2016, 03:26:57 am
content: Quote from: tyguy2 on May 22, 2016, 03:18:31 amBut the human body has temperature regulation. As long as someone is adequately hydrated their core body temperature won't change much if at all during exercise. However, their skin temperature will change enormously due to the body's temperature regulation mechanisms.These threads where people ask technical questions with complicated answers, but are unable to explain what they are doing are very frustrating.

author: Marco
author_rank: Super Contributor
timestamp: May 22, 2016, 03:58:14 am
content: Ear is no more reliable than temporal artery as far as I read (both not very).Bothtry to make corrections using guestimates of thermal resistances.Maybe you could get something useful with a sweatband with an array of LM35 and a ton of calibration (presumably heart pulse rate and strength factor in as well, because it changes perfusion rate).

author: matseng
author_rank: Frequent Contributor
timestamp: May 22, 2016, 04:10:17 am
content: Quote from: IanB on May 22, 2016, 03:26:57 amI thought so too, but some quick googling seems to indicate otherwise, the core temp do change during hard exercise. And thinking about it it seems rather reasonable - if the core temp was more or less static during exercise then you'd stop sweating almost immediately when you rest. At least I don't do that, I usually continue to sweat for 15-20 minutes after hard exercise or after a one hour fast walk in high humidity 35C/95F...

author: mtdoc
author_rank: Super Contributor
timestamp: May 22, 2016, 04:41:25 am
content: Yeah, the body will fight hard to defend a constant core temperature (brain temp in particular), but there are limits to its ability to do so.As others have pointed out, there is no highly accurate, non invasive way to measure core body temperature.

author: Fungus
author_rank: Super Contributor
timestamp: May 22, 2016, 06:21:33 am
content: Quote from: tyguy2 on May 22, 2016, 02:40:39 amAnal probe is the most accurate known method.

author: ian.rees
author_rank: Contributor
timestamp: May 22, 2016, 07:17:49 am
content: Quote from: mtdoc on May 22, 2016, 04:41:25 amThere actually are a few different temperature sensing "pills" on the market that do this. Not sure on retail cost but they apparently work very well. The ones I've seen are essentially a small battery, ISM band transmitter, IR phototransistor (to turn it on), microcontroller, etc. potted in epoxy. -Ian-

author: babysitter
author_rank: Frequent Contributor
timestamp: May 22, 2016, 07:25:23 am
content: As already mentioned, the body is working hard to stabilize the core temperature. That results in other parts trying to get rid of additional heat. Get two sensors, put one at one of the locations known to more-or-less track core temperature (cavity-like places, like armpits, anus, or at another central point (right at your belly?), and a second to a known place where regulation is done - sweat glands are often close to hair to have a wick effect helping to cool.

author: m98
author_rank: Frequent Contributor
timestamp: May 22, 2016, 09:46:19 am
content: Quote from: ian.rees on May 22, 2016, 07:17:49 amThere are actually people who designed open source capsule cameras, so nothing impossible on that side.https://hackaday.io/project/10845-tiny-wireless-capsule-cameraBut when you say that the device should be strapped on the body, you could place the temperature probe under the axilla.

author: IconicPCB
author_rank: Super Contributor
timestamp: May 22, 2016, 11:31:50 am
content: An oldie but a goodie...place the sensor on the tip of index finger and then insert finger into the appropriate canal.

author: fcb
author_rank: Super Contributor
timestamp: May 22, 2016, 12:30:08 pm
content: Calibrated LM35 on a stick, then shoved up the bum. Going to be the easiest and most accurate measurement - if not the least pleasant.Hospitals seem to have moved from under-the-tongue (mercury type) thermometer to ear-canal IR units - now they all seem to be using this IR device they wipe across the forehead (temporal artery?).I think understanding the nature of your application is important to go any further on this forum.

author: uncle_bob
author_rank: Unknown
timestamp: May 22, 2016, 12:58:06 pm
content: Quote from: tyguy2 on May 22, 2016, 03:18:31 amHiIf the person will be doing a lot of major exercise / work / moving around over a long period, then a surgically implanted device is likely the only practical way to go. Power it up and communicate with it via an inductive loop of some sort. That may not be the answer you wanted to hear, but it's probably the only one that is correct. Even that will only work just so long before it will need to be removed. Obviously you will need some major funding to do this sort of thing.Put another way: You can't do what you want to do with a surface measurement. Core is core, you can't get at it from the surface.Bob

author: Marco
author_rank: Super Contributor
timestamp: May 22, 2016, 05:39:45 pm
content: There are someinteresting experimentswith ultrasound, mostly using the liver because it's a nice big solid mostly static chunk of tissue. The backscatter method looks easiest to do on the cheap, you'd need to wear a vest to keep the transducer in place over the liver. Not really suited to an absolute temperature measurement, but working from a baseline from before exercise it might work.A smart master student or a Phd student might get it to work with a bit of R&D. Then again the massive change in blood perfusion rate during exercise might completely overwhelm the effect and it might be a complete dead end ... hard to say.

author: fcb
author_rank: Super Contributor
timestamp: May 23, 2016, 12:30:33 pm
content: http://www.hqinc.net/This appears to have been commercially available for quite some years.

author: rch
author_rank: Regular Contributor
timestamp: May 23, 2016, 02:09:31 pm
content: Quote from: fcb on May 23, 2016, 12:30:33 pmNot cheap. The pills seem not to be re-usable and cost £43 pounds each, retail, for 24-36 hours use. Plus about £2,000 for the receiver/data logger.Edit: Actually this is remarkably cheap compared with what it would cost to develop and pilot a system to do this. But still.

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 23, 2016, 08:26:53 pm
content: Quote from: tyguy2 on May 22, 2016, 03:18:31 amWhat do you want to use the data for?Monitoring of the testperson's temperatureduringthe task so that he may rest at an appropriate time?Or adding it to other dataafterthe task for some research purpose?For the latter the temperature logging pill would do.How feasable is it to transmit a signal (radio or sound) out of the body from the intestinal tract?If you could add a transmitter in the temperaturesensing pill then it can send the temperature reading without needing wires.Kinda like this:https://spinoff.nasa.gov/Spinoff2006/hm_1.html

author: mtdoc
author_rank: Super Contributor
timestamp: May 24, 2016, 05:13:58 am
content: Quote from: fcb on May 23, 2016, 12:30:33 pmThat's pretty cool!(though not non-invasive). I did not realize those were available. I'm trying to imagine their use other than research - none in medicine that I can think of.Capsule endoscopyhas been around for a while now and is very medically useful.

author: ian.rees
author_rank: Contributor
timestamp: May 24, 2016, 05:24:04 am
content: Quote from: jeroen79 on May 23, 2016, 08:26:53 pmTotally feasible - that's what some of these pill things do, via radio. -Ian-

author: jimdeane
author_rank: Regular Contributor
timestamp: May 30, 2016, 03:49:32 am
content: Quote from: Fungus on May 22, 2016, 06:21:33 amI think a deep liver probe is considered definitive.Not terribly comfortable though.

author: janekm
author_rank: Unknown
timestamp: May 30, 2016, 08:15:38 am
content: Quote from: mtdoc on May 24, 2016, 05:13:58 amNot much imagination required since their website gives application info... Sports physiology (just like what you're trying to do), Firefighting, Occupational Safety and Military...For the experiments you described this really does seem like the most sensible option, it's comparatively cheap and gives the most reliable measurement of core body temperature without any gotchas. In particular, as your subjects are going to be moving any external contact or IR sensor method is right out.

author: MarkS
author_rank: Unknown
timestamp: May 30, 2016, 09:32:30 am
content: Quote from: jimdeane on May 30, 2016, 03:49:32 amThat's what I was going to suggest. Does the person need to stay alive after the reading? If not, the liver is the best bet.