strain gauge measure over the time

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Jody
strain gauge measure over the time

Hello,

I am Jody, I come from Normandy. I am interested in hive monitoring.

I am working with two teatchers of a college to create a hive monitor.

It seems you are using strain gauge load cell to measure weight of your hive,
I have read somewhere that load cell are sensibles to temperature
and that their read derivate along the time. They should also need calibration
to prevent erronous read values.

Following this idea, we are experimenting another approach,
we would like to use liquid with a pressure sensor.

We were inspired by this experiment (in french) :
http://fablab-lannion.org/wiki/index.php?title=Suivi_des_ruches#Test:_Ut...

They use some little bags of fruit compote filled with water and a pressure sensor.

Another (more robust) example can be found at http://www.nakka-rocketry.net/hydlc.html
using brake cylinder.

Did you ever thought about this technique ?

Are you satisfied whith strain gauge ? How do you calibrate them ?

Nate
Nate's picture
Load Cell performance

Any electronic monitoring system is going to have some drift and changes over time - so if you do a hydraulic system, you'll be measuring probably pressure... you will need to re calibrate pressure which is going to be much more difficult to field calibrate. for the general beekeeper.

Load cells are fairly well characterized, so compensating for weight change due to temperature changes is a relatively simple equation.

How to field calibrate? I don't know how many people actually do this regularly, but it is actually quite simple, one simply needs a known weight. One of the Hive Tool variants Hive Control has a calibration wizard for weight built in. To use it, do the following

completely unload the load cells by hive off of the scale, start the wizard and grab the zero. now put on your known weight... enter that into the wizard and calibration should be complete.

That all said I don't think the absolute weight really makes that much difference... it's the differential weight thats interesting and gives you a clue about what's going on week to week, day to day. My supers are all slightly different weights, some have some residual pollen or honey, some have really old thick comb, some are nearly new, so the gross weight can be off but the calculated net weight and weight deltas are still just as valuable.

Adrian
Fluid weigh scale

Jody,
I have had some communication with Stephen of StephensApiary who holds a patent on using a tubular (inner tube) connected to a pressure transducer. Ref: http://www.stephensapiary.com/home/weightchange
The pressure transducers use a similar strain gauge element which can also be influenced by temperature like a load cell.
Using fluid has some drawbacks too but I do feel fluid and inner tubes could be used effectively, there needs to be a containment channel for stability, consider a plaster-of-parris mold.
Our class C3 load cells are very affordable, temperature stable pressure transducers can be costly.
I feel the temperature effects can be minimal (0.1 pound max) with precautions taken not to expose the load cell to direct sunlight.
We have collected data & done calculations that may be employed to reduce the effects if desired. There are some indications that abrupt thermal gradients cause the greatest errors.
Keep us posted on you devlopment, Best Regards,
Adrian

Adrian Ogden

Jody
I have a body scale and a

I have a body scale and a HX711 for months, my first idea was
to hack this scale but looking for tutorial some user feedbacks
seems about discouraging.

I have then met my two teachers and they were following another
approach, but it is a study case in order to learn physics to students.

I am happy to read that you use load cells and that it works for years.

One day I will hack my body scale I promise, as soon as I will be able
to power source the T° sensors and sd writer more than two days ... :-)

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