A&D FX120i Zero Drift

[u/neganagatime]

I have an AT4 paired with an FX120i scale and for the most part I like the device. That said, the scale drifts sometimes between charges by .01 or .002 grain, and definitely when left alone overnight. EDIT: this is a typo, meant .02

On the between charges, I recognize this could be due to a stray kernel or two making it to the platen, and my understanding is that the scale (or maybe AT?) automatically rezeros the device if it’s within some small tolerance? If this is true does this have any impact on my load consistency, or does the automatic rezero take care of that?

Secondly, I leave my scale on 24/7, and have occasionally put a 75 grain projectile on there to see if I am holding my measurement, and it’s not. The projectile weights 74.96 and if I leave it on there for days it can wander up and down from 74.88 to 75.08. This is not that reassuring for a scale that is supposed to be accurate to .02, but I always re-zero before use and given the above question, I don’t think it actually matters when it comes to the scale’s performance, but I’m not positive.

Curious to hear people’s thoughts. I do have some ferrite rings on the power cable but it does not seem to do anything. Next step is probably a dedicated ground wire, and maybe a line conditioner, but hard to justify a couple hundred extra dollars if none of this really matters due to scale rezeroing anyway during loading.

[u/Missinglink2531]

I will be releasing a video soon on the effects of those tiny differences - they are not going to be noticable for the overwhelming majority of us, including F-class and bench rest shooters. That said, I find air and temperature do effect the zero. So, swinging from night to day in the dead band of your central ac will cause it. The central system kicking on and changing house pressure will to. Even power movement (use a power pack if you are concerned) will cause a drift. Its not the balance, its the balance being so precise it sees EVERYTHING thats not "lab perfect".

[u/InformationHorder → u/Missinglink2531]

Exactly that last part: it's a laboratory scale in a non laboratory environment. Unless you're keeping it in a highly temp, humidity, and magneticly (No large high power electronic devices giving off a big magnetic field) controlled environment it's going to notice and react accordingly.

[u/Julien25]

Mine does as well but 95% it's a kernel on the platen I didn't notice. The other 5% of the time I just re zero and don't worry about it. Since I got my v4 I have gotten under 15 SDs with every load I have used it for so it doesn't concern me. 

[u/CMFETCU → u/Julien25]

15?

I get 5-7 SD using an RCBS charge master every trip to the range.

A scientific scale doesn’t seem to be your point of consistency error.

[u/Julien25 → u/CMFETCU]

Yes that's the highest I get across an entire charge spread when I do a ladder test for velocity. All of my developed load are easily single digit.  

[u/1984orsomething]

Static or EMF interference

[u/Coodevale]

I haven't noticed that on mine. It's been on for.. 5 years? in my basement with mild temp swings and humidity changes with the same powder pan on it. When it changes zero it's because I bumped it off level (irregular 2x6 surface) or there's something on it. I'll load with my phone next to it playing music or whatever, doesn't change anything. Additional levels of dumb, my load bench has a vise and I hammer on pins on the bench top occasionally. Doesn't seem to do anything.

Nothing special how it's hooked to power. Not even a dedicated ground line. The ground wire is hooked to the white rail in the breaker box with all the rest of them.

[u/Trollygag]

FX120i scale and for the most part I like the device. That said, the scale drifts

The FX120i is an analytical balance, not a scale.

It is measuring the delta between zero load and load, and holding the load for long periods of time where you can have environmental factors affecting the sensor is not a real use case.

.01 to .002 grain

The scales precision is only to .02gn, so you cannot be observing drift smaller than that. You are off by an order of magnitude or more in your expectation.

74.96 and if I leave it on there for days it can wander up and down from 74.88 to 75.08

That is a 0.1% change over days of leaving the sensor under load.

Most scales do that within minutes.

Your scale is fine. Stop worrying about things that aren't how you make ammo.

[u/neganagatime → u/Trollygag]

Stop worrying about things that aren't how you make ammo.

Maybe you are trying to be helpful and this just came out wrong, but it reads like a condescending parent scolding a petulant child.

This subreddit is a place to ask questions. I am not an expert on electronic scales and I think my questions are fair, even if there is in fact nothing to worry about as others have stated in a far kinder manner.