Wondering how the TS/OP will make the rodent to urinate precisely "there"...

Flip rodent on stomach (under anesthesia) with collection cup on scale below.

 

Interesting idea. What is the purpose of the oil? Thanks.

It's a medium that the urine is not miscible in. It's possible the droplets could just fall through air. The technology is called laser diffraction.
https://en.m.wikipedia.org/wiki/Laser_diffraction_analysis
I have no idea whether it could work for this application. Just a wild idea outside the box.

 

As per Alec_t's suggestion, I am trying to identify individual drops with my 1000g/0.1g scale.

With some band-pass filtering, squaring, and smoothing I was able to get something usable. Only issue is that the height the droplets need to fall is 6-12" which is a bit much.

 

As per Alec_t's suggestion, I am trying to identify individual drops with my 1000g/0.1g scale.

With some band-pass filtering, squaring, and smoothing I was able to get something usable. Only issue is that the height the droplets need to fall is 6-12" which is a bit much.

Why not put the catch container at the end of a lever with a fulcrum positioned to give, let's say, a 10:1 mechanical advantage. The container will move 10 times farther with each increase in weight and will displace the scale 1/10 the distance but with 10 times the force. You will need a low friction bearing - particulary low static friction at the fulcrum. There are a few different ways you could apply that principle. Anyway it should get you out of the noise floor.

 

You will need a low friction bearing - particulary low static friction at the fulcrum.

Yeah, probably one made of sapphire should do the trick. You could scavenge one from an old broken watch.

 

Funny you mention a watch. That was my first thought when reading the first post, to use an oscillator and disturb it with the sample. This concept is used to measure the density of a liquid, but with a consistent volume. So I dismissed it.

 

Hello,

I am interested in continuously acquiring load cell measurements with a resolution of 0.01g or lower. I need to be able to identify individual droplets of water (~0.5g) vs. time when added to the liquid container on the scale.
...
Thank you!

I was a little startled at the introduction to this thread.

I have long been assuming that a drop of water to be close to 50 micro litres, and thus 50 milli grams?

 

Why not weigh a baggie, collect urine, re-weigh baggie.

Or weigh cotton ball, collect urine with ball, re-weigh ball.

 

I would recommend the force-balance approach mentioned by RichardO (post #7) and elaborated on in the video posted by joeyd999 (post #9), but if you'd prefer something off-the-shelf you might consider the kind of scale used by reloaders to measure gunpowder. These scales usually have a resolution of 0.1 grains (1 grain = 1/7000 pound), or about 0.0065 grams. They're not expensive, and are available on MidwayUSA.com. Amazon.com also has some.

 

Why not weigh a baggie, collect urine, re-weigh baggie.

Or weigh cotton ball, collect urine with ball, re-weigh ball.

I need real-time continuous mass data.

I would recommend the force-balance approach mentioned by RichardO (post #7) and elaborated on in the video posted by joeyd999 (post #9), but if you'd prefer something off-the-shelf you might consider the kind of scale used by reloaders to measure gunpowder. These scales usually have a resolution of 0.1 grains (1 grain = 1/7000 pound), or about 0.0065 grams. They're not expensive, and are available on MidwayUSA.com. Amazon.com also has some.

Yeah, I am considering getting a finer resolution scale.

 

"I need real-time continuous mass data."

No, you would need a continuously urinating rodent.

So, now you need flow rate?
Are there any other conditions? You know, specific gravity, temp, sugar, albumin, illegal drug screen?

It would be nice to know the complete setup, before offering solutions.

I shall retire from this one.

 

Tared capillary tubes might provide a convenient way to collect the droplets and simplify the weighing process.

 

"I need real-time continuous mass data."

No, you would need a continuously urinating rodent.

So, now you need flow rate?
Are there any other conditions? You know, specific gravity, temp, sugar, albumin, illegal drug screen?

It would be nice to know the complete setup, before offering solutions.

I shall retire from this one.

OK, I am sorry that my request was not clear to you.

Real-time: data is collected with minimal delay from when the action occurred
Continuous: data is collected without interruption over time

Rodents do not urinate in a stream, they let out droplets. Not sure where I implied measuring flow-rate, though I suppose with this data an average rate could be calculated...

I do not see how those parameters are relevant to the question at hand.

I am collecting water droplets in a container on a scale and acquiring this mass data in real-time to generate plots and I was hoping someone might have experience with this. This is not the only analog parameter that I am measuring in parallel.

///

I am pursuing a few sellers of Acculab VIC-123 or VIC-303 strain-gauge balances that offer RS-232/USB output of mass data.

 

Real-time: Got it.
Continuous: Got it.
""I need real-time continuous mass data." Does mass mean "a lot or all the data? OR is that one mass measurement of one sample? Please qualify the word mass.....substitute another word.

Even if you are successful in explaining the proper measurement, I still need more context.
How do you handle the rodent. Are you retrieving each rodent, perform measurement, then tuck rodent away?
Is each rodent handled by a human? How many rodents? How many humans?
For continuous flow or total mass of flow......maybe catheters?

It's hard to read a mind.

And I have seen many rodents pee. They seem to piss like every thing else. I have raised rabbits, rats and hamsters. They all squatted and peed. Maybe lab rats are too scarred to take a good pee.

We get some real squirrelly questions here. And we can usually come up with something. IF we know all the conditions.

But adding a new condition to each solution gets old.

So.....what condition prevents the use of catheters with small receptacle taped to tail? I know....no tail.

 

Please qualify the word mass.....substitute another word.

Weight on Earth.

 

I still don't know how to approach the problem. Is the study period 24 hrs. or 1 week? Depending on local animal laws, one might stanchion the rodent. The limbs and tail would still need restraint. Collect urine from underneath. Make chute to deflect feces. If the collection device is not weighed with sample, the collection device will have to be urine non wettable.
Weighing small multiple liquid masses, is neither fast or convenient. They do have machines that dispense accurate small volumes of liquids quickly, for prepared samples.
But collecting very small masses/liquids of varying amounts on the fly is gonna be hard. The first one being that all the excreted urine is measured, and not left in/on apparatus. That's why I would add urine to known mass.

There might be another way......if you could accurately measure the amount the rodent drinks. This would be very hard to do.
It would be a matter of mass. We can measure the food intake and outtake. We can measure the rodent. If we knew the water intake, ....what's missing and leftover is the mass of the urine.
But I see no way to measure the drink. Unless the rodent is only allowed to drink twice a day and weighed afterwards.

I guess is depends on the relationship with the rodent.

 

If we knew the water intake, ....what's missing and leftover is the mass of the urine.

It's not so simple. Don't forget respiration and perspiration.

But don't worry, people have been collecting mouse pee for very long time. I'm sure the TS has most of it worked out, except the measuring part.

 

Hi all,

Old post to bump but I found a good solution using an old force-displacement transducer (Grass FT03). I threaded and marine welded a screw into the bottom of a syringe that could be threaded onto the transducer's arm.

They aren't sold anymore but one can find them on eBay for <$50. I have bought a few spares and they all have seemed to do the job very well.

Hope this helps someone down the line...