Digital Powder Scale Problem

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Hypnogator

Hypnogator

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Is it just me, or do y'all sometimes have trouble getting an exact weight on your digital powder scale? I have a relatively new Frankford Arsenal digital powder scale that I've begun using to replace my ancient Herters beam scale. This evening, while trying to throw 23.0 gr. AR-Comp, I simply could not get the scale to read 23 gr. even. I set my powder measure to throw 22.6 gr., then trickled it to 23.0 gr. Or tried to. No matter how carefully I trickled the powder, the digital scale would go from 22.8 or 22.9 to 23.1 gr. I must have tried for 10 minutes to get it to weigh an even 23 gr., then finally hauled out my old Herter's scale and followed the same procedure, trickling powder until I had the balance set to "0" on 23.0 gr. I checked each weight on the digital scale, and sure enough, I would get either 22.9 or 23.1 gr.

Is it just me, or does my digital scale just boycott 23.0 gr. for some reason? :scrutiny:
 
Just for the heck of it you can try a few other numbers like 13.0, 23.0 (again), 33.0 and see what the scale does. The scale resolves 0.1 grain so when the actual weight goes from 22.94 to 22.95 the scale should increment up to 23.0 and remain there till the actual weight goes from 23.04 to 23.05 and then increment up to 23.1. So yeah, something is amiss with this scale. This is where a good set of check weights are a nice to have. Anyway I would try several other weights and if the scale won't read certain numbers send it on a vacation back to Frankfort. There is no reason I can think of that your or any other digital scale would "boycott" any number it should display. :)

Ron
 
I had.the same problem with the FA digital scale. I replaced it with a. Gempro 250 which has been flawless for the last year.
 
My Dillon digital will not read accurately when trickling powder, I called the maker and got a long tech answer that I didn't understand most of but I think what he was saying is that when you trickle you "fool" the scale into reading an incorrect amount. Anyway I quit trickling powder on that scale.
 
Yes, it's common with them I think.

#1 They have to be warmed up to operating temp for a half hour or more before you zero them and start weighing.

#2 If battery operated, replace the battery.

#3 level the scale body on the bench so the pan poise isn't rubbing on one side of the hole it fits in in the base.

#4 Make sure there is no air-duct blowing air on it.

Bottom line is though?
Your digital scale is only accurate to 1/10 grain at best.
So it is constantly trying to decide to round up, or round down.

Your old Herters beam scale didn't go to college, or even first grade.
So it doesn't know how to round up, or down.

It just tells you what the charge weighs!
 
If your scale reads 22.7, 22.8, 22.9, 23.1, 23.2, 23.3 ... skipping only 23.0. This sounds like a quantization error. The precision of the digitizing circuitry isn't quite good enough. To test or work around this, put a small additional weight on the scale then zero it (leave the weight on the scale). This might move the error to a different reading.
 
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Thanks, all!

Your old Herters beam scale didn't go to college, or even first grade.
So it doesn't know how to round up, or down.

It just tells you what the charge weighs!
Click to expand...

Yeah, thank heavens it doesn't use Common Core math! :neener::neener::neener:

Put it on a styrofoam ammo box insert tonight, and got good consistent results with 23.8, 23.9, and 24.1 grain loads that I measured. Also measured 10 Sierra 65-gr Game King bullets and got 65.0 (5), 65.1 (1) and 65.2 (4) grains. Haven't tried replicating the 23.0 gr problem, but putting an additional weight on, then compensating sounds like an excellent idea.:cool:
 
It was probably one of BDS's, he doesn't like electronic scales.

I leave my bench scale on all the time anymore, It sits for weeks and never leaves zero. That take care of any drifting issues from a cold start up.

My plugs into 110 though.
 
tightgroup tiger said:
I leave my bench scale on all the time anymore, It sits for weeks and never leaves zero. That take care of any drifting issues from a cold start up.

My plugs into 110 though.
Click to expand...
This ^^^. Mine reads 0.00 every time I walk by and glance at it.
 
rcmodel said:
Your old Herters beam scale didn't go to college, or even first grade. So it doesn't know how to round up, or down.

It just tells you what the charge weighs!
Click to expand...
That's funny but it's so true!


tightgroup tiger said:
BDS ... he doesn't like electronic scales.
Click to expand...
I do like them but they are delicate instruments which require operation within temperature range (58F-90F for example), warm up time and/or fully charged batteries, maybe affected by florescent light ballasts (I use two CFL without issues), etc.

I like my .1 gr resolution FA DS-750 for fast powder charge weight verification and sorting of bullets. It stays on the bench along with Ohaus 10-10 for everyday use.

I also like my .02 gr resolution Gemini 20 for powder charge verification during load development, especially near max powder charges. But due to perhaps more sensitive higher resolution circuitry, I keep the Gemini 20 off the bench in a safer storage area free from all the vibration and shock of the reloading bench.

BTW, all the scales get regular zero calibration and accuracy verification with Ohaus ASTM class 6 check weights down to .1 gr. FYI, Ohaus and Gemini 20 will consistently read .1 gr check weight but FA DS-750 won't (but will read .5 gr check weight and consistently verify typical pistol powder charge weight range of 3.5-6.0 gr within .1 gr).


Hypnogator said:
putting an additional weight on, then compensating sounds like an excellent idea.
Click to expand...
Many posted this on the digital scale myth busting thread. Looks like we need to investigate this myth and verify. ;)
 
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Many posted this on the digital scale myth busting thread. Looks like we need to investigate this myth and verify.
Click to expand...

But my head still hurts from that thread.

Just out of curiosity I tried a Google of "How Digital Scales Work" and even included Powder Scales. While I think I have a handle on their operation I couldn't find a single tech website with a detailed theory of operation.

I thought about JerkandFlinch's response in this thread but don't think that is the problem. Then too, I wouldn't rule it out. I do have an old RCBS Powder Pro sitting here begging me to open it up and see what really does make it tick. Guessing it is 15 years old so I am sure the newer units work different.

Ron
 
Artofgolf said:
Hey Ron, try this link: http://www.smartweighscales.com/product/digital-jewelry-pocket-scale/

They have a Contact Us feature that may help :confused:

From the website ~ Our technical support professionals consider our consumers the highest priority and are ready to address your concerns in a most efficient manner.
Click to expand...
Thanks and it reminds me I have a Gem 20. Unfortunately they are good with regular scale questions but not so much with detailed theory of operation or making schematics available.

Now per my post #14. Does anyone know how to reassemble a digital scale and what do all these wires do? :)

Actually I took apart my RCBS Powder Pro and to my surprise it does not work the way I thought it would. Pretty simple design and it does work well. Considering it is a pretty old scale. I'll spare the technical crap unless someone really has an interest.

Ron
 
JerkandFlinch said:
@Reloadron
I believe most scales are based on a 'load cell'. See if this is what you want, http://circuitdiagram.net/load-cell-amplifier.html.
Click to expand...
Yeah, but I expected a load cell (strain gauge) circuit to drive an IA (Instrumentation Amplifier) and to an A/D (Analog to Digital) converter on my older scale. Wrong! Yeah, a load cell is where it starts:

RCBS%20Strain%20Gage.png

The load cell is a BCL-300GM (300 Gram load cell module) excited by 10 volts with a sensitivity of 1.6mV/V out. Here is the little circuit board:

RCBS%20Circuit%20Card.png

The curve is no A/D conversion. They use an AD652 V/F (Voltage to Frequency) converter. Under the display is a frequency counter module that drives the display. Below and to the right of the AD652 is a silver rectangle. That is a 4 MHz crystal used with the F/V converter.

Not at all what I expected. Today I would bet they simply use the load cell to drive an IA followed by a programmed PIC Chip of sorts and the display. Glad I took the thing apart, never would have guessed the method used.

The old scale works well and does make a nice change with powder trickled onto it. Still won't guess why the OP's scale won't display a number? Weird.

Ron
 
This ^^^. Mine reads 0.00 every time I walk by and glance at it.
Click to expand...

Did you ever consider that the scale's software is programmed NOT to allow the readout to wander when the scale is at or near zero ?

That non-fluctuating readout gives a false sense of security.
 
rfwobbly said:
Did you ever consider that the scale's software is programmed NOT to allow the readout to wander when the scale is at or near zero ?

That non-fluctuating readout gives a false sense of security.
Click to expand...
No, I had not considered that, but no false sense of security here. I calibrate it and check it with check weights before every loading session. I just leave it plugged in so I don't have to wait for it to warm up and stabilize.
 
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