Weird A&D FX120 scale issue

[Lefty Trigger]

Anybody know how or why the A&D FX120 scale would shift pan weight and still read zero? I have my Area 419 pan marked with it's exact weight 641.50 and I will run with it at 641.48 or 641.52 and not worry about it. This is easily noticed when the pan is removed to dump a charge but here lately I have caught it shifting by larger amounts but the weird part is it still reads zero when put on empty? Normally it will read 0.02 when it has shifted a little but tonight it shifted by .09 and reads zero with empty pan on and with pan off it reads 641.57.
I recalibrated it and it went back to 641.50 and my current load charges were all over by .09

 

[ronemus]

What you're seeing sounds like a response to changes in air density; the cup reads less than its true weight because it displaces air. When pressure, temperature, or humidity change the weight of the air displaced by the cup changes. Your calibration weights also displace air, so a recalibration corrects for at least some of the difference. I was an analytical chemist and instrumentation engineer before I retired, and labs doing precision measurements try to maintain very stable environments and recalibrate frequently. The highest precision measurements of weight are performed in vacuum when possible, or the weight of air displaced by the sample is accounted for.

 

[RegionRat]

Some suggestions.

Verify the bubble level and the stability of the bubble level. Make sure the bench surface isn't being affected once you start.

Verify you are warmed up and calibrate then re-check the calibration with the calibration weight before you start with loading.

Keep a thermometer nearby and keep an eye out for drafts caused by HVAC systems or natural ones.

Keep an eye out for RFI from things like motors, cell phones, relays, powerful appliances, etc.

If the humidity is very low, watch out for static issues.

With this type of unit, it is very important to watch the null (zero) on your powder pan as well as the tare weight. If you catch either one, you can stop in time to prevent rework. Sometimes powder kernels can splash out and affect the null and are tough to notice.

 

[Jager]

The FX-120i also has a zero-tracking feature (page 41 in the User Manual) which automatically shifts its zero point to account for those air density / temperature / humidity changes that might occur during a session.

That feature can be configured for sensitivity (or turned off altogether), but what the manual doesn't mention is that it only works when the scale is at zero. If you've tare'd your pan, but then have removed it (so the scale shows minus the weight of the pan), the zero-tracking feature is suspended.

Separately, as RR mentions, a single kernel of powder bouncing out of the pan and onto the platen is all you need for the scale to be off a measurable amount.

 

[powderbrake]

Are you replacing the pan in the exact same place on the platen every time?
Shifting location of the weight will shift the displayed value.

 

[Ccrider]

I see this at times. I make it a habit to unplug my scale and then recalibrate it from time to time. I know what my cup measures and if it is off by more than .04, I know something is up. Also, the number will change as the scale warms up.

 

[Ccrider]

Also, take both of the plates off the top of the scale from time to time. I have had grains of powder get between and up under the plates. Can’t explain how but it has happened more than once.

 

[RegionRat]

The gain calibration is in non-volatile memory unless you recalibrate, so the power cycle isn't helping or hurting it. The zero will be affected by a power cycle and resets.

Double checking your bubble level is important, but to learn how that affects calibration I recommend disturbing it on purpose some time just to see how it works.

Stabilize the zero and gain with your cal weight, then tweak the level just a little and then recheck the cal weight and you will learn just how careful you need to be with loads on tables, moving or walking on floors, etc. Some places are so solid that it doesn't matter what is going on, but others are sensitive to where you are sitting or standing, or leaning on a table etc. Best to play with this outside of a loading session just to be aware.

 

[Lefty Trigger]

Lots of good reply's with info to check. I have my scale on a level piece of granite counter top setting on a large sponge rubber mouse pad. Bench is secured to wall and floor. Running scale on a Tripp Lite line conditioner and mostly never turn scale off. Habit is to recalibrate scale every Wednesday. Scale pan is replaced center every time with pan guide that came with my Auto Trickler.
I do need to check into that zero tracking thing,.. could be as simple as that?
Should I "turn on" the scale with the pan on it so it reads zero with it removed insted of using Tare for the pan weight?

 

[RegionRat]

I turn on without the cup. That way the unit isn't trying to initialize with a big offset.

Then, place the cup and zero, then check gain with the cal weight and recalibrate as required.

 

[moondog]

I will unplug mine once a month then recalibrate. Wiping the pan and inside with a dryer sheet helps too. Not a 120i but the next one up.

 

[Lefty Trigger]

The FX-120i also has a zero-tracking feature (page 41 in the User Manual) which automatically shifts its zero point to account for those air density / temperature / humidity changes that might occur during a session.

That feature can be configured for sensitivity (or turned off altogether), but what the manual doesn't mention is that it only works when the scale is at zero. If you've tare'd your pan, but then have removed it (so the scale shows minus the weight of the pan), the zero-tracking feature is suspended.

Separately, as RR mentions, a single kernel of powder bouncing out of the pan and onto the platen is all you need for the scale to be off a measurable amount.

I turned off the zero tracking and it seems (so far) to have fixed my issue. Been using for over a week now and it has not happened again. Thanks for this advice!!