Hi,
regarding the question : Which part is causing the temperature dependencies?
I wasn’t expecting that, bit it is clearly the load cell! A bit disapointing, since i thought the BOSCHE Cells are better. cell is unloaded, i have 3 more sets of scales one by one is going in the chamber the next days.
What exactly does here the ordinate show, which unit and scaling?
In the previous diagram the ordinate shows the raw value of the HX711.
Here in grams :
I just have measurements with the cell unloaded, which is not optimal (since there should always be a minimum load on the cell), but still, you clearly see :
The temperature-dependency is not coming from the HX711!
I am disappointed, I thought Bosche cells are better.
I probably will do the measurments also with loaded cell, but i don’t know when, since i don’t have a lot of time right now.
I asked Bosche, but i just got the test specs and the norm (Metrological regulation for load cells) and i don’t understand the reading :)
r060-e00(1).pdf (1006,3 KB)
No, look at Bosche’s H30A datasheet, they clearly state, that they don’t require a minimum load (Mindestvorlast (E min) = 0 ), so for this load cell it is a legitimate load case. Second, this is how you can measure the temperature drift of zero (aka offset) - also needed as Bosche unfortunately does not state these drifts but instead only refers to the OIML… 8(
Better than what?
Your results are good: over a temperature range of about 58 K (-20…+38°C) the scale shows an abs. offset change of about 520 grams (could be shown as a differential error of ±260g). This is 9g / K error (for comparision: @thias ’ H30A shows about 8,7g / K). These results were achieved while stressing the cell with an ever wider temperature range than specified as compensated range (to -20 rather than to -10°C) - and no additional non-linearity has been observed. This also remains a good result.
What is the Emax for this measured H30A cell, 150 or 200kg ?
It is a 100kg Cell, so the verification interval is 100kg/3000=33grams.
I am not sure if interpret that right, but in the linked PDF
5.5.1.1 Temperature limits
Excluding temperature effects on minimum dead load
output, the load cell shall perform within the limits of
error in 5.1.1 over the temperature range of – 10 °C to
The error is defined in 5.1.1, which is about one verification interval (Table 5 Maximum permissible errors (mpe) on pattern evaluation), so max 33grams over the temperature rang of -10 to +40°C.
This is my interpretation, i am not sure if i understand that correct.
Now, all 4 scales are calibrated, the difference between the setups is not negligible.
So without individual temperature compensation - at least for me - the accuracy with the H40A is not sufficient!
Load= 20kg
first plot : without temperature compensation offset and ratio calculated @ 15°C
second plot : with temp. comp. offset(T) and ratio (T)
third plot : same as second, but y-axes is zoomed to see the actual error
What are the 4 scales / cells / setups?
HX711 and Bosche H40A.
Sorry to bother you again, @zmaier. ;-) You have in the first graph 4 lines, purple, yellow, orange and blue, this are the same setups? All with a HX711 and a Bosche H40?? 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!
Is the only difference that you are using different load cells (but all H40 from Bosche with the same max. weight?).
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.
Can you imagine what was special / other on the purple setup? Other power source, flux cleaned vs. not cleaned? screw terminals vs. cable soldered? Cut / shorted cable? Really no difference??! The purple setup is great. So in case we can find “the error” – and it is not inside the Bosche H40 this would be great! ;-) Many thanks again for the effort and time you spent!
I have absolutely no idea.
I started the thread below, because i have seen those huge differences between the setups.
To figure out why, “built” the test-chamber.
All setups have the same build-up.
Flux is cleaned
HX 711 and Load Cell is soldered with the original cable (not shortend)
Power-Supply is the same
I have no idea why?
It seems the Load Cells are really that “weak”, see my posting where I compared the temperature behavior just of the cell and just the HX711. It clearly comes from the cell itself.
What are your experiences? Should i contact Bosche with this issue?
Hi…humidity effects are rather slow and require the humidity to penetrate the epoxy that bonds the resistors to the base lever. Even the slight effect of the humidity swelling or weakening the epoxy are going to be very slight vs the temperature. Measure over several days, I doubt there is a correlation to humidity.
Is number 4 the only sensor connected with the gray/white cable in your picture in the very first post here? Is it somehow different to the others? e.g. shielding, diameter, material, twisted-or-not?
hi, what do you mean with gray/white cable, where have you seen it?
all setups are identically, no difference in cables, diameter, shielding,…
I asked Bosche three weeks ago and also last week but still no answer. I am disappointed, though buying a german product whould give me a better support. I try “Aliexpress load cells” next, cost one third.
Sorry, I just took a rough look at the image in this post and wondered to see four cables joining in a box and one of these seems different.
So the anyhow-general-underlying question is: Does something differ within the cable, taking furher distance and magnetic-fields in mind. But it’s just meant as a simple “did you check that”- queston.
Some days ago I read a FB posting about a 4 cell setup with poor reading results. They could solve the problem by a proper grounding. Did you connect the shield of the cable to ground Just brainstorming.
Yes, the shield is connected to GND.
Noch immer keine Antwort von BOSCHE, mittlerweile die dritte freundliche EMail veschickt.
Ich bin kein Großkunde, aber dennoch hätte ich mir eine Antwort erwartet.
Ich bin auf der Suche nach ähnlichen Zellen für meine weiteren Waagen, Bosche möchte ich mir nicht mehr kaufen.
Wer hat Alternativen, wenn möglich aus Europa?
Es gibt Neukigkeiten.
Ich hatte gestern ein Telefonat mit Bosche.
Dort wurde mir erklärt, die 3 Wägezellen sind nicht normal, sondern stammen aus einer anderen Charge.
Normalerweise werden die Zellen vermessen und in Genauigkeitsklassen kategorisiert.
Bei meiner Bestellung wurden die falsche Klasse ausgeliefert. Neben den auf der Homepage angebotenen Zellen gäbe es auch noch die Möglichkeit diese “nicht guten” zu kaufen. Preislich sind diese aber nur ein paar € billiger.
Mir wurde ein Austausch angeboten, ich weiß aber noch nicht ob ich mir das antun soll, der Umbau kostet Zeit - die ich nicht habe :) Weiters habe ich gefragt ob der Temperaturgang reproduzierbar ist, was eindeutig mit ja beantwortet wurde. Somit kann ich mit der individuellen Kompensation gut leben denk ich.
Wägezelle #4 stellt den Regelfall da (wenn bei der Lieferung nichts schief geht).
Einem Unternehmen welches IS0 9001 zertifiziert ist und somit einen Prozess zur Qualitätssicherung haben muss, darf sowas eigentlich nicht passieren.
Tja, ich habe dennoch 4 weitere Zellen dort bestellt, es wurde mir versichert diese werden handverlesen noch einmal überprüft. Ich werde diese aber in meiner “Klimakammer” überprüfen.
