hello,
i bought a few load cells from you guys (all 100g). On the datasheeet, it says:
Cell Repeatability Error Max: ± 50 mg
Cell Non-Linearity Max: 50 mg
Cell Hysteresis Max: 50 mg
I’m thinking about buying either the .78kg load cell or the 5kg load cell.
for all three (repeatability, non-linearity, and hysteresis), both of these load cells say
.05% FS
so, to determine accuracy for the 100g load cell, i can square each of those numbers, add them up, and take the square root to get accuracy. that looks like:
√((50mg^2)*3) = 86.6 mg = .0866 g
.0866g/100g = .000866%
so this brings me to my question - is the 100g load cell way more accurate than the other 2 options?
am i even determining accuracy correctly?
thank you
Hi,
Unfortunately, this is not the proper way to determine the accuracy of a system integration with a load cell.
Lets take the RB-Phi-118 as an example (get the datasheet here). The most important data in this case is the rated output (1.0 mv/V). This will determine the voltage output of the load cell (its sensitivity) over its full scale.
The load cell itself is a passive analog device and does not determine the accuracy of a force/weight measuring system on its own. It does however have a certain sensitivity which will affect it.
To get the accuracy of the entire system, you need to include all the components and the error they add:
]Load cell/:m]
]Amplifier (such as the RB-Onl-38)/:m]
]ADC/:m]
]Code/algorithm taking the readings/:m]
Sincerely,
Thanks for your reply. I am using a CR-1000 data logger, which (from what I understand) is really expensive and really accurate. We have it programmed to output 5V. I’m calibrating some forces using the RobotShop 100g micro load cell. So, with this load cell having 600uV/V output, we are getting a 3mV signal.
I’m trying to find the most precise (and accurate!) load cell for this setup. Is it the 5kg? the .78 kg?
that is the question I’m trying to answer.
Does that clarify?
thanks again.
Hi,
The most accurate load cell would be the one with a FS (full scale) that is closest to the loads you will be measuring. This is by far the most important criteria.
The low-cost load cells in the few hundred grams to a few kilograms all have very similar rated outputs. The most important factor will most likely be what kind of loads you are measuring compared to the maximum load it can measure.
Also, from what we can read about your data acquisition board, its accuracy is ±0.06%. With an excitation level of 5 V DC, this would mean an accuracy of ± 3 mV, which is in the range of the type of signal you will be reading. We recommend that you use an instrumental amplifier on your load cell to get a voltage output that uses the full range of 0-5 V DC so as to get a much better reading of the load cell’s measured force. You should check out the recommendations made to you earlier on the forum here.
Sincerely,
