I Identifying & Accounting for Systematic Error in Scales with 1mg Capacity

[Jhon81]

Hi everyone,
I have a scale that should weight as low as 1mg, if there was a systematic error how could I identify it and include it in my calculations?

 

[.Scott]

I assume you are accounting for Tare.
Put the container on the scale and weigh it. That's your tare.
Then put the material you want to weigh into that container and place the container back onto the scale and weigh it. Then subtract the tare.

That tare will include the weight of the container and any fixed error in the scale.

If that is the type of systematic error you are talking about, then you have your answer.
Otherwise, explain it more detail.

 

[Dale]

if there was a systematic error how could I identify it

Besides the approach mentioned above, the other approach is to use a set of calibrated weights of precisely known masses.

 

[Jhon81]

I assume you are accounting for Tare.
Put the container on the scale and weigh it. That's your tare.
Then put the material you want to weigh into that container and place the container back onto the scale and weigh it. Ten subtract the tare.

That tare will include the weight of the container and any fixed error in the scale.

If that is the type of systematic error you are talking about, then you have your answer.
Otherwise, explain it more detail.

Hi Scott,
I am going to weight a very small amount of powder ( 0.7 gm ), so I do not think that using a container will help for this small amounts.

 

[Jhon81]

Besides the approach mentioned above, the other approach is to use a set of calibrated weights of precisely known masses.

Hi Dale,
I was thinking of calibrating the scale every time I use it to minimize the error.
I have a 100 gm weight to calibrate the scale so after calibration I weight it and gave me ( 100.320gm, 100.460gm, 100.630gm), can this be a systematic error and can i correct it?

 

[.Scott]

Hi Scott,
I am going to weight a very small amount of powder ( 0.7 gm ), so I do not think that using a container will help for this small amounts.

If you are using a good scale, do not put the powder directly onto it. That's not a good way to measure and it's not a good way to treat you scale.
Use something like a thin piece of paper. Measure the paper first, then put the powder on the paper and weight them together.

Also, if you are serious about knowing you systematic variations in measurement, the topic you are interested in is called "Gage R&R".
I will look for a good link - but here are a couple until I find a good one:
https://www.managementstudyguide.com/causes-of-measurement-variation.htm
https://en.wikipedia.org/wiki/ANOVA_gauge_R&R

edit---

OK: Here is a better link:
https://support.minitab.com/en-us/m...s/gage-r-r-analyses/what-is-a-gage-r-r-study/

When you go to that link, note that there are a list of related topic listed on the left. For example, check out "Worksheet Randomization for a Gage R&R Study".

 

[Dale]

Hi Dale,
I was thinking of calibrating the scale every time I use it to minimize the error.
I have a 100 gm weight to calibrate the scale so after calibration I weight it and gave me ( 100.320gm, 100.460gm, 100.630gm), can this be a systematic error and can i correct it?

If you are trying to weigh less than 1 g then calibrating at 100 g will be suboptimal. You will be much better off calibrating to 1 g and maybe 10 g too. Be sure to check your calibration weight’s manufacturer specifications to know the tolerance and any proper handling/cleaning.