Myth busting - What causes digital scale zero drift and can it be fixed?

[jmorris]

So until a reloader has worked to minimize/eliminate reloading variables to show on target/reduce group size, need for higher resolution than 0.1 gr may not be warranted.

A “good” load won’t show a difference at short distance anyway. Why 100/200 yard benchrest guys can win with volume thrown charges, without even bothering to weigh them.

 

[LiveLife]

PM sent....

Thanks! Hope it works out.

 

[GeoDudeFlorida]

It's hard to beat a good scale. Most of the modern consumer-grade electronic scales are better than the old-school dial-o-matic triple-beams. I had one of those decades ago, bought from a high school surplus auction. Dumb to let it go but I was moving and there was no place for a precision instrument in my luggage. I don't know exactly what causes the "drift" - I use a 505 balance-beam to get my load and a Lyman pocket scale for spot-checking - but if that drift is repeatable, it can be analyzed. Capacitor leak is one explanation. Not leaking fluids but leaking charge. HF-RF can cause capacitor leak in integrated circuits. This occurs because the dielectric material is not a perfect insulator. Modern printed circuit board capacitors have a small but nonzero electrical conductivity, so each acts as a large resistance in parallel with the capacitor. Leakage can also occur through external components connected to the capacitor, like a power supply as has been mentioned. This kind of leakage is why dynamic random-access memory (DRAM) must be constantly refreshed. Impedance/resistance flux is a related cause, typically caused by "dirty" input power. Having something with an odd draw like a fan or refrigerator can dirty line input so if you have a small office 'fridge on the same circuit as your scale, you may see drift even if you've taken every other precaution.

 

[Engineer1911]

Please ANSWER the question: Did your group size get smaller?
Group size is the ultimate test of all this jibber-jabber and load cell fiddling. If the group size didn't get smaller, everyone is wasting their time chasing magical pixel dust. I've used a 1974 RCBS Model 510 scale to set my Dillon powder measure to load 223 ammo for shooting prairie dogs at 400 yards. Which has a greater influence: 1] 30 MPH gusty winds from changing directions, or 2] powder charges with ±0.05 grain accuracy ? I'm a realist, not a nit harvesting perfectionist. I reload to shoot, not achieve perfect ammo.

 

[LiveLife]

PM sent.

 

[denton]

As I've written a few times before, variations as small as .1 grain have practically no influence on group size in rifle size cartridges. FROGO207 has it right.

Now, to the OP question:

Some cheap strain gauge scales have a plastic deformation member. As far as I know, those are about impossible to completely stabilize. Better scales use a metal deformation member. Strain gauges are temperature sensitive. Some are temperature compensated for mounting on steel, and some are compensated for aluminum. Those are much more stable.

Another variable is the basic configuration of the gauge itself. The cheap design approach is a simple arrangement where a single gauge is used. That arrangement is susceptable to picking up electromagnetic interference out of the air. And it is also susceptable to drift in the power supply to the gauge. The better arrangement is four matched gauges on a single substrate, in a bridge configuration. That is a balanced arrangement that is immune to certain errors, and it uses a differential amplifier which has much better rejection of electromagnetic interference.

Strain gauge signals are on the order of a millivolt. So you need roughly 1000X amplification to get them up to an easy working level. Fortunately, instrumentation amp chips are available for a few dollars. The gain is set by the value of a single resistor. A good metal film resistor in that application helps a lot.

In the cheaper designs, interference often enters via the power cord. This shows up as erratic readings. That often can be helped with snap on ferrite filters.

So can strain gauge scales be stabilized? A lot depends on the original design.

 

[Nature Boy]

If you accept the premise that a scope that doesn’t hold zero is detrimental to accuracy then you’d have to apply the same logic to the scale that measures your powder charge.

In my opinion, achieving optimal accuracy is an exercise in eliminating causes of variation in the man/rifle/ammo system.

It your goal is minute of pie plate at 100 yards then you probably aren’t tricking charges anyway so no need to worry about +/- 1 kernel of powder. You’re probably using your scale to check that your powder thrower is in the ball park and +/- 10 kernels is likely good enough.

If you are tricking charges and your goal is to control as many variables as you can in order to achieve the most accuracy out of your system as possible, then I say it matters for a couple of reasons:

1. Having found the accuracy node for your charge weight, staying in the middle of that node helps insure that changing conditions won’t take your load out of tune.

2. Accuracy and drift issues aside, a load cell scale is slower than a mechanical balance. My time is valuable and I never have enough of it so if I can knock out 100 match rounds in half the time with twice the accuracy then the investment is worth it to me.

3. The more you control the variables in your process the more confidence you have in the ammo that comes from it. That allows you eliminate that particular cause of variation and focus on your shooting skills, i.e. rifle mechanics and wind reading. That’s when you get better.

 

[Rule3]

When an EMP strike occurs or a new ransomware through the power grid, all electronic scales will be useless.

 

[entropy]

When an EMP strike occurs or a new ransomware through the power grid, all electronic scales will be useless.

If it's an EMP strike, you won't have time for loading, and you'll have much more pressing things to attend to.

 

[Rule3]

N

If it's an EMP strike, you won't have time for loading, and you'll have much more pressing things to attend to.

No worries, I have a balance beam scale ! Canned food and a gas stove (Hurricane gear)

 

[GW Staar]

No worries, I have a balance beam scale ! Canned food and a gas stove (Hurricane gear)

Sell the scale and buy more food.........and toilet paper! ..............EMP? More likely the problem will be DAP? (last letter means politicians.)

As for scales, I have one kind to check the other kind.....safety in backups and redundancy. Yet what do you suppose the typical city-dwelling Afghan is worried about today.....probably hiding everything he has, to do with guns, reloading, or anything "western".

OP......good post.....RCBS a while back offered me their new $1000 scale for very little. (to test) I declined......too old now.....would be like casting pearls... I never have "trickled" ....and too late to start now. For what I do, my 10-10 is more than good. Gem Pro works too....and so does lesser electronic ones.....once I got rid of the Florescent above my bench and turned the heat duct another direction. Actually, I make sure the furnace is off before I use scales.

 

[FROGO207]

N


No worries, I have a balance beam scale ! Canned food and a gas stove (Hurricane gear)

Pretty much the same thing here but add a snow shovel and generator. Mine is for blizzards LOL.

 

[Nature Boy]

Gem Pro works too

So did mine. It’s a very accurate scale for the money. The problem I had was waiting for it to settle as I trickled the charges, then waiting again while adding or subtracting a few kernels to get to my charge weight target. That gets very tedious when you’re trying to load ammo for a match.

Again, please disregard if that’s not your goal. You’ll save a lot of time and a bit of money not following my advice

 

[GW Staar]

Nature Boy: The only competition I ever did was trap.....and that only 2 years. It was fun, but I think rifle and pistol competition takes a more even, patient sort....and that doesn't describe me too well. As I said, I turned down RCBS's new black Trickle machine, and told them not to waste it on me.

That said, I REALLY respect those that do well competing.....and I can see your point with the Gem Pro, even I only use it to confirm my 10-10 is still on. And I know neither of my scales is the fastest trickler to use for your kind of use (competitors who want more speed). Too bad you don't have that RCBS engineer for a friend, he would have offered it to you and you both would have come out ahead.

I wonder how RCBS's expensive black one will compare drift-wise.....it's still a strain gauge, but it has two speeds. Betting you'd still use the slow speed if you used one for comp.....but even the slow speed is faster than their other models, having two spigots.

$900 or 4 payments of $225 still pretty steep......

 

[LiveLife]

FYI: the University has an analytic lab scale on its auction site. Bidding is up to $40.

Well, our bid for the vintage Mettler lab scale didn't pan out as total cost including shipping limit of $100 was reached.

I did scan for other possible buys and look what I found, same scale I bought (Mine came with rechargeable battery) for $127+free shipping (And looks like this one has the correct 110V adapter) - https://www.ebay.com/itm/373638882428?hash=item56fe9ce47c:g:QJoAAOSwWo9gm2VT

 

[JFrank]

Perhaps at short range this may be true, however I can assure you that as distance increases the tune window becomes smaller. Mid and Long range competitor's including myself tune in one tenth grain increments be it charge weight or seating depths of one thousand.

 

[GeoDudeFlorida]

Perhaps at short range this may be true, however I can assure you that as distance increases the tune window becomes smaller. Mid and Long range competitor's including myself tune in one tenth grain increments be it charge weight or seating depths.View attachment 1019087

Yup. @Jim Watson ripped me pretty good a while back for advising a poster who wanted to load black powder .38S&W for a top-break to use Lee Dippers and the Lee chart for cartridge FFg black powder. It seems Mr. W shoots thousand yard competitions with cartridge black powder rifles and fine tunes his loads to +/-0.1gr. and felt I was being a fool, idiot, and completely irresponsible for using less accurate measures to make pistol loads for 3" and 4" 19th Century top-break revolvers. That level of fanaticism emerges from a very dark place, in my opinion; HOWEVER, nor would I want to be less than a thousand yards from Mr. W were he armed with one of his .38S&W top-break revolvers, either. He just might be able to hit me...

 

[Engineer1911]

In a future thread I hope "live life" will do a dissertation on Marital Sex, Positions and Satisfaction . I hope I can stay awake for all the [adjective omitted] details.

 

[Jim Watson]

Geez, what could have come over me. There is probably nothing better suited to BP dipper loading than .38 S&W for shooting in cheap old revolvers. BPCR match ammo will still be weighed in accordance with the recommendations of the Sharps Rifle Co.

When I was in college chemistry lab, the latest and greatest in weighing was the chain balance. No fiddly little weights to move along the bar, just roll the chain in and out.

My old PACT is not obviously subject to drift over a loading session.
I seldom turn it off and the room is air conditioned.
Hit 'tare' and check weigh when I start work and I am off and running.
Not obviously affected by fluorescent lighting but it is plugged in to a cheap 'surge protector' shared by nothing else while weighing.

 

[GeoDudeFlorida]

There is probably nothing better suited to BP dipper loading than .38 S&W for shooting in cheap old revolvers.

IIRC, that thread was kind of long and winding so you probably thought it was about long-range cartridge. It happens. However, I do believe I will still stay at more than a thousand yards if you are armed only with a .38S&W BP revolver and not in a mood for trifling.
Momma didn't raise no fools.

 

[Jim Watson]

I maintain repeaters for Social Purposes.

 

[FROGO207]

And when the smoke clears.........we have a winner!

 

[LiveLife]

OK everyone, looks like we are "drifting" away from the OP (pun intended).

The thread title was,

Myth busting - What causes digital scale zero drift and can it be fixed?
​

And the focus of discussion was whether digital scales drifting zero (confirmed) but more importantly what causes zero drift (already identified and listed) and how we can fix it (ongoing discussion).

Of course, I am always interested in what other variables improve accuracy in terms of reducing group size regardless of firearm type and range but this thread discussion is focused on digital scale zero drift

 

[GeoDudeFlorida]

OK everyone, looks like we are "drifting" away from the OP (pun intended).

The thread title was,

Myth busting - What causes digital scale zero drift and can it be fixed?
​

And the focus of discussion was whether digital scales drifting zero (confirmed) but more importantly what causes zero drift (already identified and listed) and how we can fix it (ongoing discussion).

Of course, I am always interested in what other variables improve accuracy in terms of reducing group size regardless of firearm type and range but this thread discussion is focused on digital scale zero drift

Different but kind of related: where I work we have very high precision drug/sample freezers and refrigerators. We buy hardware and program monitoring systems and websites for those freezers and refrigerators. A few years ago we noticed some hard to explain drift in the readings that didn't correspond with the internal monitoring units. After some investigation we found the monitoring units built into the freezers and refrigerators had some pretty sophisticated circuit isolation technology built into them. We moved all of our wall-outlet powered sensor units to isolated circuits, got them into really good insulators designed for -50C and used battery units for all of the sensor IC's - and the drift went away. The compressors kicking on were sending RF powerful enough to interrupt the sensor IC's for a few milliseconds and recalibration took a few clock cycles. So we had reading drifts of +/- .5C - like an open door or hot-spot might produce - only in spikes, not curves. It's kind of surprising how the trails of little causes can accumulate into a noticeable effect - lights, compressors, cell phones, suitcase nukes, A/C vents...

 

[Rule3]

IIRC, that thread was kind of long and winding so you probably thought it was about long-range cartridge. It happens. .

A long and winding thread? (Long and winding road)

Say it isn't so!! Never!