Strain gauge load cell tests in a DIY climate chamber

[didilamken]

Ich teste gerade 2 x FiPy in meinem Gewächshaus. FiPy1 mit China-Wägezelle (links) und FiPy2 mit Bosche H40A (rechts).

Daten vom FiPy1: t_i_5 wurde von der Sonne beschienen

Daten vom FiPy2: t_o liegt im Schatten direkt an der H40A

Die Temperaturkompensation der Bosche H40A ist ersichtlich.

[hsors]

Very interesting, thanks much !
May I ask you what was your test setting in term of measure taking ? More precisely, did you reset the offset of the load cell each time you took a measure (seems to be the normal way of operating with any scale that is not permanently loaded) or did you establish the offset once for all and took all your measures with this same offset (when the scale is always loaded, it’s impossible to reset the offset at each measure) ?

[poesel]

@hsors

This is why I believe we only need to measure the slope and intercept of the offset

Ah - I misunderstood. I thought you were talking generally about measuring. If you have a calibrated scale its of course different. Then the amount of preliminary measurement necessary is inverse proportional to the trust you put into the datasheet of the manufacturer.

[clemens]

@hsors

Bath room type (it’s a total disaster)

Hello Henri, nice to have you at hiveeyes on board! Welcome! You may have seen this thread with a “nice” collection of the same experiences. Feel free to add details the audience may not know yet!

Scales with bathroom load sensors

This thread is just for monitoring other projects that uses the cheap 3 wire load sensors – and fail – in the most cases. We are talking about this around $ 9 cheap 50 kg load cells that are used in bathroom scales, e.g. the model sold by Sparfun: The first trial to use this kind of sensor for bee scales is direcly from the founder of Sparkfun Nathan Seidle: The Internet of Bees: Adding Sensors to Monitor Hive Health https://makezine.com/projects/bees-sensors-monitor-hive-health/ It is …

@hsors

Now it you calculate the offset at a given temperature and measure the weight at another temperature, this doesn’t work any more because the offset is varying with temperature.

Good explaind! So in terms of scale calibration factors we have in our code e.g.

const long loadCellZeroOffset = -80186;
const long loadCellKgDivider  = -21738;

and the variable loadCellZeroOffset is the bad guy in our game!

One of the most interesting parts in this thread is:

@clemens

So why has the purple one nearly no temperature effect and the yellow one such a big? I fear I do not understand the difference of the 4 “settings”. May you clarify this, thanks!

@zmaier

The 4 lines are 4 setups each with a HX711 and a H40A-100kg.
Why setup 4 is good, all others not, i don’t know.
I have no clue.

@zmaier used the same settings, the same model of the load cell (“the good one”) and still temperatur effects! And the effect ist different for differen individual load cells. So not the model is the reference for an compensation factor but each cell. That makes building mass hive scales not easy, you have to test and set the compensation factor for every single cell.

My conclusion would be, take a not sooo sensitve load cell and forget about compensating the temperature.

[hsors]

Thanks much Clemens, I appreciate the help and the guidance.

In your experience is the firmness of the frame supporting the load cell an important factor for the measure accuracy ? I am still waiting for the hopefully final double H frame and I am questioning a little bit the frame I am using for testing.