What equipment can reliably measure very small weight changes?

I need to measure changes in human weight down to single grams. I do not care about the overall weight of an individual, but rather variations in weight due to breathing, evaporation, or outside influences.

What equipment is available to perform these sensitive weight measurements with research level accuracy?

I have been referred to LVDT systems, but I can't find any applications for these systems that would be appropriate for the range of weight that I am measuring along with the accuracy that I need. A reference to this type of information for LVDT systems or any other equipment would be very helpful. Thanks!

2013-06-20T20:18:43Z

Additional Information:
I have ways to deal with moisture and breathing issues in my overall measurements, but I need to get a measurement on each individual to set a baseline. I'm more interested in the equipment that is available. Again, I'm not interested in total weight, but rather variations, but a scale that has a max of 100kg probably won't have the capacity I need for some "larger" americans. I appreciate the suggestions, but I am still interested in other options. Does anybody know if LVDTs can be used for this sort of project? Thanks.

adaviel2013-06-20T16:53:20Z

Favorite Answer

A&D apparently make a scale that will weight 101kg to 1g accuracy

I suspect it would be very hard to measure the weight of a living person that accurately. You might have them sit or lie down, and then average the readings over several seconds

10

Mike1942f2013-06-21T02:14:24Z

Having dealt with digital scales and weight people, I don't think you have the slightest chance of carrying out this project with any reliability - The results of shifting of body position or clinching muscles are going to overwhelm and readings of a few grams (if that much) from breathing) and the slightest change of position will change the geometry of the pressure on the strain gauges used for measurement. Further, the latency of digital scales (or the time it takes to read analog if you go that route) is longer than the breathing cycle.
If I had to guess, I would say that 1 milliliter (1 gram of water) is about what is lost in moisture in the breath (and sweat?) in the course of trying to take a reading of a minute or so and getting readings more quickly will reduce accuracy or increase flutter (variability) in readings.
The tidal volume of the lungs is about 0.5 liter http://en.wikipedia.org/wiki/Lung_volumes#Values
The density of the air is 1225 g/m3 http://en.wikipedia.org/wiki/Density_of_air
A cubic meter is 1000 liters
So the tidal air is under 1/2 gram - so your desire to measure to a gram will not be enough.

10

Lex Lodge2013-06-21T02:44:06Z

To my understanding these kind of measures are done per the individual factor. A breathing mask, maybe a cotton garment to absorb moisture, that kind of stuff; and then you aggregate the information into an average value.
On the off chance it means anything to you; I do know of a state run lab which had to move. They had something called a "balance table." At their new site a train track one quarter mile away was interfering with their readings.

10

Anonymous2013-06-21T12:13:18Z

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Anonymous2013-06-21T12:12:45Z

I'd advise you take a took at http://tinyurl.com/m8qbhgs to get some stuff

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