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Old March 27, 2014, 07:25 AM   #1
SWThomas
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Ways to make a digital scale more reliable?

I'm currently using a Dillon digital scale to weigh my powder charges. I like the size and the ease of use..., and the fact that it matches all my other Dillon stuff.... But it seems to be pretty inconsistent when used with the power adapter plugged in. I haven't used it enough with just batteries to get an idea of the consistency.

Are these scales more consistent when used with just batteries to power them? Are there ways to overcome the power fluctuations that make these scales inconsistent when they're plugged into an outlet?
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Old March 27, 2014, 08:00 AM   #2
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The only way you will find this out for yourself is if you spend $10 and get yourself a weight calibration kit.

http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

These things are simple and work. It'll will give you peace of mind when reloading, or tell you that you need a new scale.
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Old March 27, 2014, 08:45 AM   #3
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Use a power strip that is also a line conditioner.
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Old March 27, 2014, 08:59 AM   #4
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To check for consistency you could use anything that has a fixed weight and just check it periodically to see if it shows the same reading over time. Calibration is essential too, but in this case to check for variation you don't need to use a calibration weight specifically, just something that isn't changing.

Other general tips for good weighing:
  • Allow the balance and power supply to warm-up before use. I turn mine on 24 hours before I plan to use them.
  • Make sure the balance is level, stays level, and doesn't get moved during a weighing session.
  • Avoid areas where there are air currents, and avoid creating them when you are weighing.
  • Make sure the balance is sited somewhere free from vibration.
  • Static can sometimes be a problem. Try wiping down the balance, tray, pan etc with anti-static wipes. I have anti-static mats on my benches.
  • *Some* balances use 'zero-tracking' algorithms to avoid accumulating drift. For this to work the balance needs to spend some time at (or near) zero during each weighing cycle, so it can 'home-in' on zero.

    For example, if you zero the balance with the empty powder pan on the tray, but then in your cycle you load the pan from a powder measure before placing it on the balance, the balance is never 'seeing' zero, so zero-tracking is not able to function. In these cases you can zero the balance *without* the powder pan, then work to the weight of the pan plus charge - the balance is then at zero all the time the pan is off the balance so it has plenty of time to track zero.

  • Some folks suggest avoiding fluorescent lighting and other sources of electrical and electromagnetic noise. I've never personally experienced a problem with this; my balances are very sensitive units and my loading room is also a server room with a rack full of electronics and fluorescent lighting. Maybe my balances are better shielded and more resistant to noise than others though.
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Old March 27, 2014, 09:07 AM   #5
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SW,

Edit: I was composing as others posted, so some of this is redundant information.

Electronic scales can be sensitive to any kind of interference or temperature shift. A good general principle, if you are going to plug one into a wall outlet, is to use a line filter (the signal conditioner GWS mentioned). If you have an old computer uninterruptable powder supply (UPS) whose battery has died, this makes a good choice. You can also buy line filters. Note that this is not the same thing as a simple surge protector. Surge protectors short out high voltages. Line filters have inductors and capacitors that eliminate high frequency interference that can appear in your wiring when you operate a motor or a computer or a fluorescent light. Especially if it's on the same circuit. The UPS needs one because the internal oscillator that makes line power from the battery during a power failure also generates a fairly extreme amount of that kind of interference if it isn't filtered.

There are times when the filter doesn't cut it. This is when there is direct radio frequency interference through the air. The main trick is to avoid conventional fluorescent lamps being too close to the unit. Same with operating computer power supplies too near. You can line a box with aluminum foil and set the scale inside to reduce this, but it's usually easier just to avoid any sort of electronic lighting. Near the scale is one place where the good old fashioned incandescent lamp is a better choice.

Temperature stability and avoiding drafts is important, too. A lot of strain gauge load cell type lab scales keep current through the load cell bridge even when they are not in use so that the bridge temperature remains stabilized. The best advice for line operation is to turn the thing on a good 20 minutes before you mess with zeroing it or calibrating it. I keep mine on a small granite surface plate that sits on a couple of layers of medium pile carpet scrap. The heavy mass changes temperature slowly and the carpet mitigates vibration passing through to it. My scale has an integral draft shield. If yours does not, the plate and carpet scrap can be set down inside a box so the walls become the draft shield. Mainly, though, just don't breath on it or have an air register or anything with a fan that blows toward it.

In winter it can be important to avoid static electric charge on your hands, as the static can attract or repel the scale pan enough to make it register. This is also true for a beam balance, but the greater mass makes the effect slower to act. Using one of the electronics worker's anti-static wrist bands to bleed charge of off can help with weighing in dry conditions. The straps have a resistance in them that prevents sudden discharge as sparks from occurring. Put on on your wrist. If you want your hands free, you ankle works just as well. You just have to remember it's there before you walk away.

Battery operation doesn't allow long warm up. You just have to zero for every measurement unless you get a unit that's very stable.

I find that last point the most frustrating aspect of electronic scales. I have several for various purposes, three of which are sensitive enough for powder weighing. Their stability is variable. One of them is just plain poor. One that's a battery operated unit has proven super reliable, but the guy I got it from dropped the line because of problems with some units. And that seems to be a pattern. Some units are just more stable than others, and you have to hope to get a good one. Price doesn't always tell you which you will end up with, though it probably improves the warranty to pay a bit more.
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Old March 27, 2014, 11:56 AM   #6
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I live in as dry a climate as you are likely to find (well short of the S.W. US on a hot day with their under 10% humidity)

I have never had static issues.

I have a cheap Frankfurth (sp?)

If it drifts off, I re-zero it and its fine. Cross check with a beam type occasionally and its more accurate than the beam can show.

the re-zero is not annoying, I just check to be sure its gone back to the tare weight and if not re-zero. The pan acts as a calibration as its weight is know (and written down in case I have a mental zark). If its more than a grain off ever I can't see it on a cross check and thats good enough for me.

It does not seem a high price to pay or that hard, just part of the routine to get an accurate device thats a tough one to make high quality at an affordable price.
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Old March 27, 2014, 04:17 PM   #7
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I think I got lucky. I have a $30 MTM battery-operated scale that is dead-nuts reliable. I check it often because I keep believing that because its cheap and small its bound to go to junk any minute... but 3 years later its still dead-on and doesn't require anything fancy. I do have to monitor the batteries. I have noticed it starts to act wonky when the batteries begin to lose voltage. Rechargeable batteries are great for this.
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Old March 29, 2014, 01:06 PM   #8
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Batteries going low will cause a problem. I should replace mine.

However, I would go tiht a Lithium Camera battery if the scale has that size, they last forever in the application.

I don't know that the rate of use on the small electronic scales justifies it.

Not sure if what I posted is in the category or making it more reliable, but it does ensure the accuracy.

Working with calibrating sensors, what you want to start out with is zero and you get that with the scale as there is no weight on it (if its not zero then the auto zero does that)

The other thing you want is for the scaling to work right. That is a bit trickier concept. Basically your scale works in voltage not weight. Weight is a conversion process.

Inside your sale may have .1 volt per grain (no idea what it is that is just an example).

Scaling means you put a known weight on it and then it adjusts its internal calculation to tell it that it needs to adjust itself to reflect that.

Calibration weights are the normal way to start. but a pan weight if done on a calibrated scale does that as well making an auto confirmation each time you take it off and see what the negative tare is.

As the pan weighs about 145 gr plus or minus, that is above what you are weigh charge wise (at least for the calibers I am working with!) That is the best scaling as you don't care if at 500 grs its worked its way off as you are proportionally closer down lower. If you aren't going to the moon you don't need moon accuracy.

Using the beam to check is required as you can get non linear resutls in some areas while the scale will show good for a given point. Supposedly that cannot happen per experts on larger scaled I have talked to but I am extremely skeptical and the more cross checks you can get the better off you are.
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Old March 29, 2014, 02:20 PM   #9
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Quote:
Scaling means you put a known weight on it and then it adjusts its internal calculation to tell it that it needs to adjust itself to reflect that.
^This!

I sometimes forget to calibrate with my weight, but it is a critical step to do before any loading session!
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Old March 29, 2014, 04:00 PM   #10
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Quote:
Originally Posted by RC-20
I live in as dry a climate as you are likely to find (well short of the S.W. US on a hot day with their under 10% humidity)

I have never had static issues.
That surprises me. In winter, without a strap, I can get a scale to shift half a grain just by approaching its pan with my hand. Of course, static build up is affected by a number of factors: forced dry air circulation, what your rugs and clothes are made of, how good an insulator your shoe soles are, etc.
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Old March 29, 2014, 07:29 PM   #11
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The only one of the problems I have seen is the air movement. Only because I blow powder off it and see it change then.

I have seen what you describe with switchgear meters, but I don't pass my hand over the scale either (I will next time I have it out to see).

Buttons are at the bottom and the pan extends over the scale and with the tab my hand stays fairly far away.

I use a trickler to bring it up to weight (tending to rod powders) so my hand is even further away.

I don't know if I just got lucky or its that combination of low cost and not overly sensitive.

Some days its more stable than others but again as I check the negative pan weight each time (or thats the drill, I do miss sometimes but maybe once or twice out of 50)

What I do see is while the pan weight is 144.5, sometimes its 144.6 and sometimes 144.5 and it might go up to 144.6 and down to 144.4. I suspect thats the round up function and its more like a grain one way or the other.

For me it really does not make a difference if one round of 50 is actually at 50.5 or 50.3, my shooting is no where near that tight, all those loaded in a session come out to a grain accuracy and I tend to shoot them in those quantities till depleted and then the next batch goes in another box while I finish the current one off.

I can't see that much variation on the beam so as long as it stays there I let it go. If it changes out its 144.3/.2 and then I just zero it again.
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Old March 29, 2014, 07:33 PM   #12
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Quote:
Ways to make a digital scale more reliable?
1. Replace it with a beam scale.
2. See #1.
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Old April 1, 2014, 11:21 AM   #13
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Marco,

I've often commented that the plus side to a beam balance is that gravity doesn't go out of calibration. But I say that just because it sounds glib; it doesn't actually matter to a beam balance. Beam balances actually compare masses rather than weight. That is, when the counterweights on the beam are set to 10 grains, the same amount of powder that brings the pointer to zero on earth will also bring it to zero the moon, even though it only weighs 1/5 as much there. It'll still be the same quantity of powder. It'll just take 5 times longer for the pointer to settle. So, other than changing settling time, the beam balance would ignore a change in gravity, even if it did go out of calibration.

An electronic scale will simply refuse to calibrate on the moon unless it was specially designed to have a super wide scaling range and extra stable and low noise transducer electronics so that a five fold demand on resolution didn't give it severe display jitters. And if you start out with it calibrated on earth and don't recalibrate when you get to the moon, it will read 1/5 the earth weight and mislead you about the amount of powder you are loading.

The two drawbacks to beam balances are that if they don't have a good, positive transport lock that takes the beams off the knife edge, they can be too delicate to take back and forth for range loading without eventually incurring damage. My first electronic scale was purchased just to overcome that limitation, and to let me use a more compact draft shielding box. The other limitation is just that beam balances are slower settling, which adds up when you are weighing a large number of things, but which some don't care about.

As a human factors consideration, if you make an error in your counterweight notch placement (easy to do with the 0.1 grain weight on some units), you may never notice the erroneous weight it is giving you when the pointer is zeroed. The digital scale display, on the other hand, makes an error obvious.



RC20,

Display jitter can be either averaging or least significant digit bit count error. In any case, using a scale to weigh charges is pretty much a rifle loading practice because of the greater inherent precision most rifles have over most handguns, and which typically employ charges great enough that 0.1 grains is a pretty small percentage of the whole. If you have a medium power rifle, like a .308 shooting 45 grains of powder, then an error of 0.1 grains is about the same error you'll get from ambient temperature changing about 3°F outside. You really don't want loads that touchy about exact charge. It's best to have one you can vary half a grain or more without changing POI, if you can it. Something sensitive to an error of 0.1 grains of powder will lead to having to change long range sight come-ups with the time of day.
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Old April 2, 2014, 12:52 PM   #14
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Unclenick, reloading on the moon? That would get stuff out of the way of Christmas tree ornaments in the garage!
I tried using a digital scale and had the same calibration/battery/static electricty/poltergeist issues. All those things that you do have with a digital but not with a beam scale. I went back to the beam and tossed the digital. I need it to work, now, accurately. Not guessing games.
Another thing I will mention is I really like the Lee PPM volumetric system that gives you a table of powder density factors and you calculate the value to dial in, and confirm with your scale. It works great! And reduces my perceived need to weigh every charge.
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Old April 2, 2014, 01:10 PM   #15
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I graduated from designing electronic equipment to management, but the problems associated with the sensors used in these scales persists. I could describe the issues in detail (PM me if you are that inclined / bored / curious) but will jump to the chase here:

There are really only a few "precise" (high repeatability) solutions:
1) invest in a superior scale that provides auto calibrates. This is likely $300-$1k, or more.
2) *frequently* use a calibrated test standard (weight) within your scale drift and tolerance (if your scale drifts 10 grains hourly and you have to be within 10 grains max error, then you need to recalibrate more frequently than hourly.)
3) as noted above, buy a beam balance (there are a few $$$$ automatic versions)
-or-
4) live with the drift and uncertainty.
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Old April 3, 2014, 08:45 AM   #16
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Marco,

If you haven't done so before, pop over to Accurate Powder's web site and click on the bottles in one of the line (rifle or pistol) images. Below the written description they give you the nominal VMD numbers (plural because they have both an English and metric VMDs) to their powder manufacturers.

Those VMD's don't all match the Lee tables exactly, probably just because Lee didn't happen to have an exactly average lot sample when they took their readings. The site also includes the bulk density tolerances that determine the exact VMD each lot may have. They have numbers that vary from as low as ±2.2% to as high as ±5.6%, IIRC. I presume lot-to-lot variation like that exist throughout the industry. I'm sure you weigh what comes out of the PPM to veryify, but I thought anyone else reading the thread should be aware the VMD's can vary with lot numbers.

BTW, Wester Powders provides the same feature on the site for their Ramshot line. I wish other manufacturers would do it.
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Old April 3, 2014, 07:14 PM   #17
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Some folks have put an AC powder adapter with the right DC voltage and current connected to the battery terminals of their battery powered digital scales. Such modifications put the same voltage to the scale all the time. Most folks with a bit of electricity and soldering knowledge can do it. Radio Shack has adapters for just about any output voltage and current. Be careful you don't get one that puts out too much current else your scale will send up a smoke signal telling you it died.
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Old April 4, 2014, 08:37 AM   #18
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If the voltage is right, the scale won't draw too much current, regardless of the power supply's current capacity. However, an oversized simple power supply that is basically just a transformer with a diode bridge and filter capacitor will tend to deliver voltage that's on the high side when it has too light a load. A regulated power supply won't do that, so it's best to get a regulated type. Radio Shack has sold them for awhile. They do cost more than an unregulated one. But that regulator also reduces the amount of hum and noise superimposed on the DC voltage supplied.

Today there are fewer transformers as switching supplies that have integral regulators take over. However, that doesn't cure all ills. Like the cheaper transformers, there is no Faraday shield to reduce capacitive coupling between the line and the delivered voltage, so high frequency noise from other devices sharing the AC line can still be coupled in and cause reading jitters. A line filter is still needed if you have that problem with an adapter.
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