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I want to build a connected scale that I can set coffee powder (for example) on it and check over the internet how much of coffee I still have without going to see it.

Usually all loadcells have a creep factor, like this one, which has a creep factor of 0.1%FS/10MIN Does this mean that the output will decrease by 0.1% each 10 minutes at full scale? If this is true, then the connected scale is not a viable product?

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  • \$\begingroup\$ What is the minimum weight you want to detect? What is the maximum weight you want to detect? Once you provide these parameters you can evaluate if the .1%FS creep is acceptable to you. I would assume that in a static calibration you will want to let your calibration weight sit on the sensor for 10 min to allow it to creep. \$\endgroup\$
    – Tinkerer
    Commented Apr 10, 2014 at 21:03
  • \$\begingroup\$ No, it doesn't mean that. Most of the creep should take place in the first part of the stated creep time interval. There should be little creep in the next 10 minutes. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Apr 10, 2014 at 21:10
  • \$\begingroup\$ @gerrishp2 I would like to detect a maximum weight of 5kg and with a precision of 1 gram \$\endgroup\$
    – koike
    Commented Apr 10, 2014 at 21:53
  • \$\begingroup\$ @SpehroPefhany Then I think I didn't understand what creep means, according to this load cell glossary, creep is "The change in LOAD CELL SIGNAL occurring with time while under load and with all environmental conditions and other variables remaining constant. Normally expressed in units of % of applied load over a specified time interval. It is common for characterization to be measured with a constant load at or near CAPACITY." \$\endgroup\$
    – koike
    Commented Apr 10, 2014 at 21:55

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Typical creep (parameter "1") of a Vishay load cell over the stated 30 minute interval.

enter image description here

The Vishay document states:

OIML recommendation R76 requires a 30 minute test and specifies an error limit for this time period, as well as the last 10 minutes (20 to 30 minutes). NTEP requires a one hour test and specifies an error limit for this period.

OIML is "Organization Internationale de Metrologie Legale" (International Organization of Legal Metrology) European standard.

NTEP is "National Type Evaluation Program" of NIST (National Institute of Standards and Technology) US standard.

You might expect inexpensive load cells would not have full accuracy specifications for "Trade" use, but most should behave reasonably and not creep much after the first 10-20 minutes.

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  • \$\begingroup\$ In the document you provided is written "Creep: The change in load cell output occurring with time while under constant load (>90% of the load cell capacity) ...", it means that if my load is < 90%, then the output of the bridge composed by this loadcell will remain constant and I won't have problems? \$\endgroup\$
    – koike
    Commented Apr 10, 2014 at 22:20
  • \$\begingroup\$ 2.1.2 Creep and MDLOR in that document says creep typically would decrease proportional to load. So if the creep is 50gm at 90% load (45kg), it might be 5gm at 9% load (4.5kg). \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Apr 10, 2014 at 23:02
  • \$\begingroup\$ Thanks (again) for you help. I do really want to understand, but I am getting a hard time to understand what Creep and MDLOR means (and to understand this graphic). Do you have any reference that could help me? I am reading some explanations in some sites but I think I am missing something. \$\endgroup\$
    – koike
    Commented Apr 11, 2014 at 10:41
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    \$\begingroup\$ If you don't need to measure to extremely high accuracy, you don't really need to understand it. If you apply a weight, the output immediately goes to one value (say 1000g), then slowly, over time, creeps upward to a slightly higher value (say 1001g) and then pretty much stops. If you're only trying to measure to (say) +/-2.5g you can ignore it. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Apr 11, 2014 at 10:48
  • \$\begingroup\$ ok, I re-read the explanation of the vishay datasheet and that is what I understand: V0 is the ideal output with no load (if MDLOR was zero) and VL is the ideal output with a load L (if the creep was zero). Then if the creep is 0.1% over 30 minutes and the MDLOR is 0.2% over 10 minutes, when I put a load L on it, the output will reach VL and it can increase 0.1% over 30 minutes and stabilizes, when I take off this load L, the output will reach the V0 but can decrease 0.2% over 10 minutes and then stabilizes. Is this right? \$\endgroup\$
    – koike
    Commented Apr 11, 2014 at 18:38

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